diff -urNp coreutils-7.2-orig/doc/coreutils.texi coreutils-7.2/doc/coreutils.texi
--- coreutils-7.2-orig/doc/coreutils.texi 2009-03-29 19:44:10.000000000 +0200
+++ coreutils-7.2/doc/coreutils.texi 2010-01-12 15:49:19.000000000 +0100
@@ -6100,8 +6100,9 @@ Exit status:
1 minor problems (e.g., failure to access a file or directory not
specified as a command line argument. This happens when listing a
directory in which entries are actively being removed or renamed.)
-2 serious trouble (e.g., memory exhausted, invalid option or failure
- to access file or directory specified as a command line argument)
+2 serious trouble (e.g., memory exhausted, invalid option, failure
+ to access a file or directory specified as a command line argument
+ or a directory loop)
@end display
Also see @ref{Common options}.
diff -urNp coreutils-7.2-orig/doc/coreutils.texi.orig coreutils-7.2/doc/coreutils.texi.orig
--- coreutils-7.2-orig/doc/coreutils.texi.orig 1970-01-01 01:00:00.000000000 +0100
+++ coreutils-7.2/doc/coreutils.texi.orig 2009-03-29 19:44:10.000000000 +0200
@@ -0,0 +1,15550 @@
+\input texinfo
+@c %**start of header
+@setfilename coreutils.info
+@settitle @sc{gnu} Coreutils
+
+@c %**end of header
+
+@include version.texi
+@include constants.texi
+
+@c Define new indices.
+@defcodeindex op
+@defcodeindex fl
+
+@c Put everything in one index (arbitrarily chosen to be the concept index).
+@syncodeindex fl cp
+@syncodeindex fn cp
+@syncodeindex ky cp
+@syncodeindex op cp
+@syncodeindex pg cp
+@syncodeindex vr cp
+
+@dircategory Basics
+@direntry
+* Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
+* Common options: (coreutils)Common options. Common options.
+* File permissions: (coreutils)File permissions. Access modes.
+* Date input formats: (coreutils)Date input formats.
+@end direntry
+
+@c FIXME: the following need documentation
+@c * [: (coreutils)[ invocation. File/string tests.
+@c * pinky: (coreutils)pinky invocation. FIXME.
+@c * mktemp: (coreutils)mktemp invocation. FIXME.
+
+@dircategory Individual utilities
+@direntry
+* arch: (coreutils)arch invocation. Print machine hardware name.
+* base64: (coreutils)base64 invocation. Base64 encode/decode data.
+* basename: (coreutils)basename invocation. Strip directory and suffix.
+* cat: (coreutils)cat invocation. Concatenate and write files.
+* chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
+* chgrp: (coreutils)chgrp invocation. Change file groups.
+* chmod: (coreutils)chmod invocation. Change file permissions.
+* chown: (coreutils)chown invocation. Change file owners/groups.
+* chroot: (coreutils)chroot invocation. Specify the root directory.
+* cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
+* comm: (coreutils)comm invocation. Compare sorted files by line.
+* cp: (coreutils)cp invocation. Copy files.
+* csplit: (coreutils)csplit invocation. Split by context.
+* cut: (coreutils)cut invocation. Print selected parts of lines.
+* date: (coreutils)date invocation. Print/set system date and time.
+* dd: (coreutils)dd invocation. Copy and convert a file.
+* df: (coreutils)df invocation. Report file system disk usage.
+* dir: (coreutils)dir invocation. List directories briefly.
+* dircolors: (coreutils)dircolors invocation. Color setup for ls.
+* dirname: (coreutils)dirname invocation. Strip non-directory suffix.
+* du: (coreutils)du invocation. Report on disk usage.
+* echo: (coreutils)echo invocation. Print a line of text.
+* env: (coreutils)env invocation. Modify the environment.
+* expand: (coreutils)expand invocation. Convert tabs to spaces.
+* expr: (coreutils)expr invocation. Evaluate expressions.
+* factor: (coreutils)factor invocation. Print prime factors
+* false: (coreutils)false invocation. Do nothing, unsuccessfully.
+* fmt: (coreutils)fmt invocation. Reformat paragraph text.
+* fold: (coreutils)fold invocation. Wrap long input lines.
+* groups: (coreutils)groups invocation. Print group names a user is in.
+* head: (coreutils)head invocation. Output the first part of files.
+* hostid: (coreutils)hostid invocation. Print numeric host identifier.
+* hostname: (coreutils)hostname invocation. Print or set system name.
+* id: (coreutils)id invocation. Print user identity.
+* install: (coreutils)install invocation. Copy and change attributes.
+* join: (coreutils)join invocation. Join lines on a common field.
+* kill: (coreutils)kill invocation. Send a signal to processes.
+* link: (coreutils)link invocation. Make hard links between files.
+* ln: (coreutils)ln invocation. Make links between files.
+* logname: (coreutils)logname invocation. Print current login name.
+* ls: (coreutils)ls invocation. List directory contents.
+* md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
+* mkdir: (coreutils)mkdir invocation. Create directories.
+* mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
+* mknod: (coreutils)mknod invocation. Create special files.
+* mv: (coreutils)mv invocation. Rename files.
+* nice: (coreutils)nice invocation. Modify niceness.
+* nl: (coreutils)nl invocation. Number lines and write files.
+* nohup: (coreutils)nohup invocation. Immunize to hangups.
+* od: (coreutils)od invocation. Dump files in octal, etc.
+* paste: (coreutils)paste invocation. Merge lines of files.
+* pathchk: (coreutils)pathchk invocation. Check file name portability.
+* pr: (coreutils)pr invocation. Paginate or columnate files.
+* printenv: (coreutils)printenv invocation. Print environment variables.
+* printf: (coreutils)printf invocation. Format and print data.
+* ptx: (coreutils)ptx invocation. Produce permuted indexes.
+* pwd: (coreutils)pwd invocation. Print working directory.
+* readlink: (coreutils)readlink invocation. Print referent of a symlink.
+* rm: (coreutils)rm invocation. Remove files.
+* rmdir: (coreutils)rmdir invocation. Remove empty directories.
+* runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
+* seq: (coreutils)seq invocation. Print numeric sequences
+* sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
+* sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
+* shred: (coreutils)shred invocation. Remove files more securely.
+* shuf: (coreutils)shuf invocation. Shuffling text files.
+* sleep: (coreutils)sleep invocation. Delay for a specified time.
+* sort: (coreutils)sort invocation. Sort text files.
+* split: (coreutils)split invocation. Split into fixed-size pieces.
+* stat: (coreutils)stat invocation. Report file(system) status.
+* stty: (coreutils)stty invocation. Print/change terminal settings.
+* su: (coreutils)su invocation. Modify user and group ID.
+* sum: (coreutils)sum invocation. Print traditional checksum.
+* sync: (coreutils)sync invocation. Synchronize memory and disk.
+* tac: (coreutils)tac invocation. Reverse files.
+* tail: (coreutils)tail invocation. Output the last part of files.
+* tee: (coreutils)tee invocation. Redirect to multiple files.
+* test: (coreutils)test invocation. File/string tests.
+* timeout: (coreutils)timeout invocation. Run with time limit.
+* touch: (coreutils)touch invocation. Change file timestamps.
+* tr: (coreutils)tr invocation. Translate characters.
+* true: (coreutils)true invocation. Do nothing, successfully.
+* truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
+* tsort: (coreutils)tsort invocation. Topological sort.
+* tty: (coreutils)tty invocation. Print terminal name.
+* uname: (coreutils)uname invocation. Print system information.
+* unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
+* uniq: (coreutils)uniq invocation. Uniquify files.
+* unlink: (coreutils)unlink invocation. Removal via unlink(2).
+* uptime: (coreutils)uptime invocation. Print uptime and load.
+* users: (coreutils)users invocation. Print current user names.
+* vdir: (coreutils)vdir invocation. List directories verbosely.
+* wc: (coreutils)wc invocation. Line, word, and byte counts.
+* who: (coreutils)who invocation. Print who is logged in.
+* whoami: (coreutils)whoami invocation. Print effective user ID.
+* yes: (coreutils)yes invocation. Print a string indefinitely.
+@end direntry
+
+@copying
+This manual documents version @value{VERSION} of the @sc{gnu} core
+utilities, including the standard programs for text and file manipulation.
+
+Copyright @copyright{} 1994-1996, 2000-2009 Free Software Foundation, Inc.
+
+@quotation
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts. A copy of the license is included in the section entitled ``GNU
+Free Documentation License''.
+@end quotation
+@end copying
+
+@titlepage
+@title @sc{gnu} @code{Coreutils}
+@subtitle Core GNU utilities
+@subtitle for version @value{VERSION}, @value{UPDATED}
+@author David MacKenzie et al.
+
+@page
+@vskip 0pt plus 1filll
+@insertcopying
+@end titlepage
+@shortcontents
+@contents
+
+@ifnottex
+@node Top
+@top GNU Coreutils
+
+@insertcopying
+@end ifnottex
+
+@cindex core utilities
+@cindex text utilities
+@cindex shell utilities
+@cindex file utilities
+
+@menu
+* Introduction:: Caveats, overview, and authors.
+* Common options:: Common options.
+* Output of entire files:: cat tac nl od
+* Formatting file contents:: fmt pr fold
+* Output of parts of files:: head tail split csplit
+* Summarizing files:: wc sum cksum md5sum sha1sum sha2
+* Operating on sorted files:: sort shuf uniq comm ptx tsort
+* Operating on fields within a line:: cut paste join
+* Operating on characters:: tr expand unexpand
+* Directory listing:: ls dir vdir dircolors
+* Basic operations:: cp dd install mv rm shred
+* Special file types:: ln mkdir rmdir mkfifo mknod
+* Changing file attributes:: chgrp chmod chown touch
+* Disk usage:: df du stat sync truncate
+* Printing text:: echo printf yes
+* Conditions:: false true test expr
+* Redirection:: tee
+* File name manipulation:: dirname basename pathchk
+* Working context:: pwd stty printenv tty
+* User information:: id logname whoami groups users who
+* System context:: date uname hostname hostid uptime
+* SELinux context:: chcon runcon
+* Modified command invocation:: chroot env nice nohup su timeout
+* Process control:: kill
+* Delaying:: sleep
+* Numeric operations:: factor seq
+* File permissions:: Access modes.
+* Date input formats:: Specifying date strings.
+* Opening the software toolbox:: The software tools philosophy.
+* GNU Free Documentation License:: Copying and sharing this manual.
+* Concept index:: General index.
+
+@detailmenu
+ --- The Detailed Node Listing ---
+
+Common Options
+
+* Exit status:: Indicating program success or failure.
+* Backup options:: Backup options
+* Block size:: Block size
+* Signal specifications:: Specifying signals
+* Disambiguating names and IDs:: chgrp and chown owner and group syntax
+* Random sources:: Sources of random data
+* Target directory:: Target directory
+* Trailing slashes:: Trailing slashes
+* Traversing symlinks:: Traversing symlinks to directories
+* Treating / specially:: Treating / specially
+* Standards conformance:: Standards conformance
+
+Output of entire files
+
+* cat invocation:: Concatenate and write files.
+* tac invocation:: Concatenate and write files in reverse.
+* nl invocation:: Number lines and write files.
+* od invocation:: Write files in octal or other formats.
+* base64 invocation:: Transform data into printable data.
+
+Formatting file contents
+
+* fmt invocation:: Reformat paragraph text.
+* pr invocation:: Paginate or columnate files for printing.
+* fold invocation:: Wrap input lines to fit in specified width.
+
+Output of parts of files
+
+* head invocation:: Output the first part of files.
+* tail invocation:: Output the last part of files.
+* split invocation:: Split a file into fixed-size pieces.
+* csplit invocation:: Split a file into context-determined pieces.
+
+Summarizing files
+
+* wc invocation:: Print newline, word, and byte counts.
+* sum invocation:: Print checksum and block counts.
+* cksum invocation:: Print CRC checksum and byte counts.
+* md5sum invocation:: Print or check MD5 digests.
+* sha1sum invocation:: Print or check SHA-1 digests.
+* sha2 utilities:: Print or check SHA-2 digests.
+
+Operating on sorted files
+
+* sort invocation:: Sort text files.
+* shuf invocation:: Shuffle text files.
+* uniq invocation:: Uniquify files.
+* comm invocation:: Compare two sorted files line by line.
+* ptx invocation:: Produce a permuted index of file contents.
+* tsort invocation:: Topological sort.
+
+@command{ptx}: Produce permuted indexes
+
+* General options in ptx:: Options which affect general program behavior.
+* Charset selection in ptx:: Underlying character set considerations.
+* Input processing in ptx:: Input fields, contexts, and keyword selection.
+* Output formatting in ptx:: Types of output format, and sizing the fields.
+* Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
+
+Operating on fields within a line
+
+* cut invocation:: Print selected parts of lines.
+* paste invocation:: Merge lines of files.
+* join invocation:: Join lines on a common field.
+
+Operating on characters
+
+* tr invocation:: Translate, squeeze, and/or delete characters.
+* expand invocation:: Convert tabs to spaces.
+* unexpand invocation:: Convert spaces to tabs.
+
+@command{tr}: Translate, squeeze, and/or delete characters
+
+* Character sets:: Specifying sets of characters.
+* Translating:: Changing one set of characters to another.
+* Squeezing:: Squeezing repeats and deleting.
+
+Directory listing
+
+* ls invocation:: List directory contents
+* dir invocation:: Briefly list directory contents
+* vdir invocation:: Verbosely list directory contents
+* dircolors invocation:: Color setup for @command{ls}
+
+@command{ls}: List directory contents
+
+* Which files are listed:: Which files are listed
+* What information is listed:: What information is listed
+* Sorting the output:: Sorting the output
+* More details about version sort:: More details about version sort
+* General output formatting:: General output formatting
+* Formatting the file names:: Formatting the file names
+
+Basic operations
+
+* cp invocation:: Copy files and directories
+* dd invocation:: Convert and copy a file
+* install invocation:: Copy files and set attributes
+* mv invocation:: Move (rename) files
+* rm invocation:: Remove files or directories
+* shred invocation:: Remove files more securely
+
+Special file types
+
+* link invocation:: Make a hard link via the link syscall
+* ln invocation:: Make links between files
+* mkdir invocation:: Make directories
+* mkfifo invocation:: Make FIFOs (named pipes)
+* mknod invocation:: Make block or character special files
+* readlink invocation:: Print the referent of a symbolic link
+* rmdir invocation:: Remove empty directories
+* unlink invocation:: Remove files via unlink syscall
+
+Changing file attributes
+
+* chown invocation:: Change file owner and group
+* chgrp invocation:: Change group ownership
+* chmod invocation:: Change access permissions
+* touch invocation:: Change file timestamps
+
+Disk usage
+
+* df invocation:: Report file system disk space usage
+* du invocation:: Estimate file space usage
+* stat invocation:: Report file or file system status
+* sync invocation:: Synchronize data on disk with memory
+* truncate invocation:: Shrink or extend the size of a file
+
+Printing text
+
+* echo invocation:: Print a line of text
+* printf invocation:: Format and print data
+* yes invocation:: Print a string until interrupted
+
+Conditions
+
+* false invocation:: Do nothing, unsuccessfully
+* true invocation:: Do nothing, successfully
+* test invocation:: Check file types and compare values
+* expr invocation:: Evaluate expressions
+
+@command{test}: Check file types and compare values
+
+* File type tests:: File type tests
+* Access permission tests:: Access permission tests
+* File characteristic tests:: File characteristic tests
+* String tests:: String tests
+* Numeric tests:: Numeric tests
+
+@command{expr}: Evaluate expression
+
+* String expressions:: + : match substr index length
+* Numeric expressions:: + - * / %
+* Relations for expr:: | & < <= = == != >= >
+* Examples of expr:: Examples of using @command{expr}
+
+Redirection
+
+* tee invocation:: Redirect output to multiple files or processes
+
+File name manipulation
+
+* basename invocation:: Strip directory and suffix from a file name
+* dirname invocation:: Strip non-directory suffix from a file name
+* pathchk invocation:: Check file name validity and portability
+
+Working context
+
+* pwd invocation:: Print working directory
+* stty invocation:: Print or change terminal characteristics
+* printenv invocation:: Print all or some environment variables
+* tty invocation:: Print file name of terminal on standard input
+
+@command{stty}: Print or change terminal characteristics
+
+* Control:: Control settings
+* Input:: Input settings
+* Output:: Output settings
+* Local:: Local settings
+* Combination:: Combination settings
+* Characters:: Special characters
+* Special:: Special settings
+
+User information
+
+* id invocation:: Print user identity
+* logname invocation:: Print current login name
+* whoami invocation:: Print effective user ID
+* groups invocation:: Print group names a user is in
+* users invocation:: Print login names of users currently logged in
+* who invocation:: Print who is currently logged in
+
+System context
+
+* arch invocation:: Print machine hardware name
+* date invocation:: Print or set system date and time
+* uname invocation:: Print system information
+* hostname invocation:: Print or set system name
+* hostid invocation:: Print numeric host identifier
+* uptime invocation:: Print system uptime and load
+
+@command{date}: Print or set system date and time
+
+* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
+* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
+* Literal conversion specifiers:: %[%nt]
+* Padding and other flags:: Pad with zeros, spaces, etc.
+* Setting the time:: Changing the system clock.
+* Options for date:: Instead of the current time.
+* Date input formats:: Specifying date strings.
+* Examples of date:: Examples.
+
+SELinux context
+* chcon invocation:: Change SELinux context of file
+* runcon invocation:: Run a command in specified SELinux context
+
+Modified command invocation
+
+* chroot invocation:: Run a command with a different root directory
+* env invocation:: Run a command in a modified environment
+* nice invocation:: Run a command with modified niceness
+* nohup invocation:: Run a command immune to hangups
+* su invocation:: Run a command with substitute user and group ID
+* timeout invocation:: Run a command with a time limit
+
+Process control
+
+* kill invocation:: Sending a signal to processes.
+
+Delaying
+
+* sleep invocation:: Delay for a specified time
+
+Numeric operations
+
+* factor invocation:: Print prime factors
+* seq invocation:: Print numeric sequences
+
+File permissions
+
+* Mode Structure:: Structure of file mode bits.
+* Symbolic Modes:: Mnemonic representation of file mode bits.
+* Numeric Modes:: File mode bits as octal numbers.
+* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.
+
+Date input formats
+
+* General date syntax:: Common rules.
+* Calendar date items:: 19 Dec 1994.
+* Time of day items:: 9:20pm.
+* Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
+* Day of week items:: Monday and others.
+* Relative items in date strings:: next tuesday, 2 years ago.
+* Pure numbers in date strings:: 19931219, 1440.
+* Seconds since the Epoch:: @@1078100502.
+* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
+* Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
+
+Opening the software toolbox
+
+* Toolbox introduction:: Toolbox introduction
+* I/O redirection:: I/O redirection
+* The who command:: The @command{who} command
+* The cut command:: The @command{cut} command
+* The sort command:: The @command{sort} command
+* The uniq command:: The @command{uniq} command
+* Putting the tools together:: Putting the tools together
+
+Copying This Manual
+
+* GNU Free Documentation License:: Copying and sharing this manual.
+
+@end detailmenu
+@end menu
+
+
+@node Introduction
+@chapter Introduction
+
+This manual is a work in progress: many sections make no attempt to explain
+basic concepts in a way suitable for novices. Thus, if you are interested,
+please get involved in improving this manual. The entire @sc{gnu} community
+will benefit.
+
+@cindex @acronym{POSIX}
+The @sc{gnu} utilities documented here are mostly compatible with the
+@acronym{POSIX} standard.
+@cindex bugs, reporting
+Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
+to include the version number, machine architecture, input files, and
+any other information needed to reproduce the bug: your input, what you
+expected, what you got, and why it is wrong. Diffs are welcome, but
+please include a description of the problem as well, since this is
+sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
+
+@cindex Berry, K.
+@cindex Paterson, R.
+@cindex Stallman, R.
+@cindex Pinard, F.
+@cindex MacKenzie, D.
+@cindex Meyering, J.
+@cindex Youmans, B.
+This manual was originally derived from the Unix man pages in the
+distributions, which were written by David MacKenzie and updated by Jim
+Meyering. What you are reading now is the authoritative documentation
+for these utilities; the man pages are no longer being maintained. The
+original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
+Pinard did the initial conversion to Texinfo format. Karl Berry did the
+indexing, some reorganization, and editing of the results. Brian
+Youmans of the Free Software Foundation office staff combined the
+manuals for textutils, fileutils, and sh-utils to produce the present
+omnibus manual. Richard Stallman contributed his usual invaluable
+insights to the overall process.
+
+@node Common options
+@chapter Common options
+
+@macro optBackup
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+@end macro
+
+@macro optBackupSuffix
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+Append @var{suffix} to each backup file made with @option{-b}.
+@xref{Backup options}.
+@end macro
+
+@macro optTargetDirectory
+@item -t @var{directory}
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex -t
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Specify the destination @var{directory}.
+@xref{Target directory}.
+@end macro
+
+@macro optNoTargetDirectory
+@item -T
+@itemx --no-target-directory
+@opindex -T
+@opindex --no-target-directory
+@cindex target directory
+@cindex destination directory
+Do not treat the last operand specially when it is a directory or a
+symbolic link to a directory. @xref{Target directory}.
+@end macro
+
+@macro optSi
+@itemx --si
+@opindex --si
+@cindex SI output
+Append an SI-style abbreviation to each size, such as @samp{M} for
+megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
+1,000,000 bytes. This option is equivalent to
+@option{--block-size=si}. Use the @option{-h} or
+@option{--human-readable} option if
+you prefer powers of 1024.
+@end macro
+
+@macro optHumanReadable
+@item -h
+@itemx --human-readable
+@opindex -h
+@opindex --human-readable
+@cindex human-readable output
+Append a size letter to each size, such as @samp{M} for mebibytes.
+Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
+This option is equivalent to @option{--block-size=human-readable}.
+Use the @option{--si} option if you prefer powers of 1000.
+@end macro
+
+@macro optStripTrailingSlashes
+@itemx @w{@kbd{--strip-trailing-slashes}}
+@opindex --strip-trailing-slashes
+@cindex stripping trailing slashes
+Remove any trailing slashes from each @var{source} argument.
+@xref{Trailing slashes}.
+@end macro
+
+@macro mayConflictWithShellBuiltIn{cmd}
+@cindex conflicts with shell built-ins
+@cindex built-in shell commands, conflicts with
+Due to shell aliases and built-in @command{\cmd\} command, using an
+unadorned @command{\cmd\} interactively or in a script may get you
+different functionality than that described here. Invoke it via
+@command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
+from the shell.
+
+@end macro
+
+@macro multiplierSuffixes{varName}
+@ignore
+Appending @samp{b} multiplies @var{\varName\} by 512,
+@samp{kB} by 1000, @samp{K} by 1024,
+@samp{MB} by 1000*1000, @samp{M} by 1024*1024,
+@samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
+and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
+@end ignore
+@var{\varName\} is a number which may have one of the following
+multiplicative suffixes:
+@example
+@samp{b} => 512 ("blocks")
+@samp{KB} => 1000 (KiloBytes)
+@samp{K} => 1024 (KibiBytes)
+@samp{MB} => 1000*1000 (MegaBytes)
+@samp{M} => 1024*1024 (MebiBytes)
+@samp{GB} => 1000*1000*1000 (GigaBytes)
+@samp{G} => 1024*1024*1024 (GibiBytes)
+@end example
+and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
+@end macro
+
+@c FIXME: same as above, but no ``blocks'' line.
+@macro multiplierSuffixesNoBlocks{varName}
+@var{\varName\} is a number which may have one of the following
+multiplicative suffixes:
+@example
+@samp{KB} => 1000 (KiloBytes)
+@samp{K} => 1024 (KibiBytes)
+@samp{MB} => 1000*1000 (MegaBytes)
+@samp{M} => 1024*1024 (MebiBytes)
+@samp{GB} => 1000*1000*1000 (GigaBytes)
+@samp{G} => 1024*1024*1024 (GibiBytes)
+@end example
+and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
+@end macro
+
+@cindex common options
+
+Certain options are available in all of these programs. Rather than
+writing identical descriptions for each of the programs, they are
+described here. (In fact, every @sc{gnu} program accepts (or should accept)
+these options.)
+
+@vindex POSIXLY_CORRECT
+Normally options and operands can appear in any order, and programs act
+as if all the options appear before any operands. For example,
+@samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
+@samp{:} is an option-argument of @option{-t}. However, if the
+@env{POSIXLY_CORRECT} environment variable is set, options must appear
+before operands, unless otherwise specified for a particular command.
+
+A few programs can usefully have trailing operands with leading
+@samp{-}. With such a program, options must precede operands even if
+@env{POSIXLY_CORRECT} is not set, and this fact is noted in the
+program description. For example, the @command{env} command's options
+must appear before its operands, since in some cases the operands
+specify a command that itself contains options.
+
+Most programs that accept long options recognize unambiguous
+abbreviations of those options. For example, @samp{rmdir
+--ignore-fail-on-non-empty} can be invoked as @samp{rmdir
+--ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
+@samp{ls --h}, are identified as such.
+
+Some of these programs recognize the @option{--help} and @option{--version}
+options only when one of them is the sole command line argument. For
+these programs, abbreviations of the long options are not always recognized.
+
+@table @samp
+
+@item --help
+@opindex --help
+@cindex help, online
+Print a usage message listing all available options, then exit successfully.
+
+@item --version
+@opindex --version
+@cindex version number, finding
+Print the version number, then exit successfully.
+
+@item --
+@opindex --
+@cindex option delimiter
+Delimit the option list. Later arguments, if any, are treated as
+operands even if they begin with @samp{-}. For example, @samp{sort --
+-r} reads from the file named @file{-r}.
+
+@end table
+
+@cindex standard input
+@cindex standard output
+A single @samp{-} operand is not really an option, though it looks like one. It
+stands for standard input, or for standard output if that is clear from
+the context. For example, @samp{sort -} reads from standard input,
+and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
+extra copy of its input to standard output. Unless otherwise
+specified, @samp{-} can appear as any operand that requires a file
+name.
+
+@menu
+* Exit status:: Indicating program success or failure.
+* Backup options:: -b -S, in some programs.
+* Block size:: BLOCK_SIZE and --block-size, in some programs.
+* Signal specifications:: Specifying signals using the --signal option.
+* Disambiguating names and IDs:: chgrp and chown owner and group syntax
+* Random sources:: --random-source, in some programs.
+* Target directory:: Specifying a target directory, in some programs.
+* Trailing slashes:: --strip-trailing-slashes, in some programs.
+* Traversing symlinks:: -H, -L, or -P, in some programs.
+* Treating / specially:: --preserve-root and --no-preserve-root.
+* Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
+* Standards conformance:: Conformance to the @acronym{POSIX} standard.
+@end menu
+
+
+@node Exit status
+@section Exit status
+
+@macro exitstatus
+An exit status of zero indicates success,
+and a nonzero value indicates failure.
+@end macro
+
+Nearly every command invocation yields an integral @dfn{exit status}
+that can be used to change how other commands work.
+For the vast majority of commands, an exit status of zero indicates
+success. Failure is indicated by a nonzero value---typically
+@samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
+requires only that it be nonzero.
+
+However, some of the programs documented here do produce
+other exit status values and a few associate different
+meanings with the values @samp{0} and @samp{1}.
+Here are some of the exceptions:
+@command{chroot}, @command{env}, @command{expr},
+@command{nice}, @command{nohup}, @command{printenv}, @command{sort},
+@command{su}, @command{test}, @command{timeout}, @command{tty}.
+
+
+@node Backup options
+@section Backup options
+
+@cindex backup options
+
+Some @sc{gnu} programs (at least @command{cp}, @command{install},
+@command{ln}, and @command{mv}) optionally make backups of files
+before writing new versions.
+These options control the details of these backups. The options are also
+briefly mentioned in the descriptions of the particular programs.
+
+@table @samp
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+Make a backup of each file that would otherwise be overwritten or removed.
+Without this option, the original versions are destroyed.
+Use @var{method} to determine the type of backups to make.
+When this option is used but @var{method} is not specified,
+then the value of the @env{VERSION_CONTROL}
+environment variable is used. And if @env{VERSION_CONTROL} is not set,
+the default backup type is @samp{existing}.
+
+Note that the short form of this option, @option{-b} does not accept any
+argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
+
+@vindex version-control @r{Emacs variable}
+This option corresponds to the Emacs variable @samp{version-control};
+the values for @var{method} are the same as those used in Emacs.
+This option also accepts more descriptive names.
+The valid @var{method}s are (unique abbreviations are accepted):
+
+@table @samp
+@item none
+@itemx off
+@opindex none @r{backup method}
+Never make backups.
+
+@item numbered
+@itemx t
+@opindex numbered @r{backup method}
+Always make numbered backups.
+
+@item existing
+@itemx nil
+@opindex existing @r{backup method}
+Make numbered backups of files that already have them, simple backups
+of the others.
+
+@item simple
+@itemx never
+@opindex simple @r{backup method}
+Always make simple backups. Please note @samp{never} is not to be
+confused with @samp{none}.
+
+@end table
+
+@item -S @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -S
+@opindex --suffix
+@cindex backup suffix
+@vindex SIMPLE_BACKUP_SUFFIX
+Append @var{suffix} to each backup file made with @option{-b}. If this
+option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
+environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
+set, the default is @samp{~}, just as in Emacs.
+
+@end table
+
+@node Block size
+@section Block size
+
+@cindex block size
+
+Some @sc{gnu} programs (at least @command{df}, @command{du}, and
+@command{ls}) display sizes in ``blocks''. You can adjust the block size
+and method of display to make sizes easier to read. The block size
+used for display is independent of any file system block size.
+Fractional block counts are rounded up to the nearest integer.
+
+@opindex --block-size=@var{size}
+@vindex BLOCKSIZE
+@vindex BLOCK_SIZE
+@vindex DF_BLOCK_SIZE
+@vindex DU_BLOCK_SIZE
+@vindex LS_BLOCK_SIZE
+@vindex POSIXLY_CORRECT@r{, and block size}
+
+The default block size is chosen by examining the following environment
+variables in turn; the first one that is set determines the block size.
+
+@table @code
+
+@item DF_BLOCK_SIZE
+This specifies the default block size for the @command{df} command.
+Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
+@env{LS_BLOCK_SIZE} for @command{ls}.
+
+@item BLOCK_SIZE
+This specifies the default block size for all three commands, if the
+above command-specific environment variables are not set.
+
+@item BLOCKSIZE
+This specifies the default block size for all values that are normally
+printed as blocks, if neither @env{BLOCK_SIZE} nor the above
+command-specific environment variables are set. Unlike the other
+environment variables, @env{BLOCKSIZE} does not affect values that are
+normally printed as byte counts, e.g., the file sizes contained in
+@code{ls -l} output.
+
+@item POSIXLY_CORRECT
+If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
+@env{BLOCKSIZE} is set, but this variable is set, the block size
+defaults to 512.
+
+@end table
+
+If none of the above environment variables are set, the block size
+currently defaults to 1024 bytes in most contexts, but this number may
+change in the future. For @command{ls} file sizes, the block size
+defaults to 1 byte.
+
+@cindex human-readable output
+@cindex SI output
+
+A block size specification can be a positive integer specifying the number
+of bytes per block, or it can be @code{human-readable} or @code{si} to
+select a human-readable format. Integers may be followed by suffixes
+that are upward compatible with the
+@uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
+for decimal multiples and with the
+@uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
+prefixes for binary multiples}.
+
+With human-readable formats, output sizes are followed by a size letter
+such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
+powers of 1024; @samp{M} stands for 1,048,576 bytes.
+@code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
+@samp{B}; @samp{MB} stands for 1,000,000 bytes.
+
+@vindex LC_NUMERIC
+A block size specification preceded by @samp{'} causes output sizes to
+be displayed with thousands separators. The @env{LC_NUMERIC} locale
+specifies the thousands separator and grouping. For example, in an
+American English locale, @samp{--block-size="'1kB"} would cause a size
+of 1234000 bytes to be displayed as @samp{1,234}. In the default C
+locale, there is no thousands separator so a leading @samp{'} has no
+effect.
+
+An integer block size can be followed by a suffix to specify a
+multiple of that size. A bare size letter,
+or one followed by @samp{iB}, specifies
+a multiple using powers of 1024. A size letter followed by @samp{B}
+specifies powers of 1000 instead. For example, @samp{1M} and
+@samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
+equivalent to @samp{1000000}.
+
+A plain suffix without a preceding integer acts as if @samp{1} were
+prepended, except that it causes a size indication to be appended to
+the output. For example, @samp{--block-size="kB"} displays 3000 as
+@samp{3kB}.
+
+The following suffixes are defined. Large sizes like @code{1Y}
+may be rejected by your computer due to limitations of its arithmetic.
+
+@table @samp
+@item kB
+@cindex kilobyte, definition of
+kilobyte: @math{10^3 = 1000}.
+@item k
+@itemx K
+@itemx KiB
+@cindex kibibyte, definition of
+kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
+@samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
+@acronym{POSIX} use @samp{k} to mean @samp{KiB}.
+@item MB
+@cindex megabyte, definition of
+megabyte: @math{10^6 = 1,000,000}.
+@item M
+@itemx MiB
+@cindex mebibyte, definition of
+mebibyte: @math{2^{20} = 1,048,576}.
+@item GB
+@cindex gigabyte, definition of
+gigabyte: @math{10^9 = 1,000,000,000}.
+@item G
+@itemx GiB
+@cindex gibibyte, definition of
+gibibyte: @math{2^{30} = 1,073,741,824}.
+@item TB
+@cindex terabyte, definition of
+terabyte: @math{10^{12} = 1,000,000,000,000}.
+@item T
+@itemx TiB
+@cindex tebibyte, definition of
+tebibyte: @math{2^{40} = 1,099,511,627,776}.
+@item PB
+@cindex petabyte, definition of
+petabyte: @math{10^{15} = 1,000,000,000,000,000}.
+@item P
+@itemx PiB
+@cindex pebibyte, definition of
+pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
+@item EB
+@cindex exabyte, definition of
+exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
+@item E
+@itemx EiB
+@cindex exbibyte, definition of
+exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
+@item ZB
+@cindex zettabyte, definition of
+zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
+@item Z
+@itemx ZiB
+@math{2^{70} = 1,180,591,620,717,411,303,424}.
+(@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
+@item YB
+@cindex yottabyte, definition of
+yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
+@item Y
+@itemx YiB
+@math{2^{80} = 1,208,925,819,614,629,174,706,176}.
+(@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
+@end table
+
+@opindex -k
+@opindex -h
+@opindex --block-size
+@opindex --human-readable
+@opindex --si
+
+Block size defaults can be overridden by an explicit
+@option{--block-size=@var{size}} option. The @option{-k}
+option is equivalent to @option{--block-size=1K}, which
+is the default unless the @env{POSIXLY_CORRECT} environment variable is
+set. The @option{-h} or @option{--human-readable} option is equivalent to
+@option{--block-size=human-readable}. The @option{--si} option is
+equivalent to @option{--block-size=si}.
+
+@node Signal specifications
+@section Signal specifications
+@cindex signals, specifying
+
+A @var{signal} may be a signal name like @samp{HUP}, or a signal
+number like @samp{1}, or an exit status of a process terminated by the
+signal. A signal name can be given in canonical form or prefixed by
+@samp{SIG}. The case of the letters is ignored. The following signal names
+and numbers are supported on all @acronym{POSIX} compliant systems:
+
+@table @samp
+@item HUP
+1. Hangup.
+@item INT
+2. Terminal interrupt.
+@item QUIT
+3. Terminal quit.
+@item ABRT
+6. Process abort.
+@item KILL
+9. Kill (cannot be caught or ignored).
+@item ALRM
+14. Alarm Clock.
+@item TERM
+15. Termination.
+@end table
+
+@noindent
+Other supported signal names have system-dependent corresponding
+numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
+support the following signals:
+
+@table @samp
+@item BUS
+Access to an undefined portion of a memory object.
+@item CHLD
+Child process terminated, stopped, or continued.
+@item CONT
+Continue executing, if stopped.
+@item FPE
+Erroneous arithmetic operation.
+@item ILL
+Illegal Instruction.
+@item PIPE
+Write on a pipe with no one to read it.
+@item SEGV
+Invalid memory reference.
+@item STOP
+Stop executing (cannot be caught or ignored).
+@item TSTP
+Terminal stop.
+@item TTIN
+Background process attempting read.
+@item TTOU
+Background process attempting write.
+@item URG
+High bandwidth data is available at a socket.
+@item USR1
+User-defined signal 1.
+@item USR2
+User-defined signal 2.
+@end table
+
+@noindent
+@acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
+also support the following signals:
+
+@table @samp
+@item POLL
+Pollable event.
+@item PROF
+Profiling timer expired.
+@item SYS
+Bad system call.
+@item TRAP
+Trace/breakpoint trap.
+@item VTALRM
+Virtual timer expired.
+@item XCPU
+CPU time limit exceeded.
+@item XFSZ
+File size limit exceeded.
+@end table
+
+@noindent
+@acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
+also support at least eight real-time signals called @samp{RTMIN},
+@samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
+
+@node Disambiguating names and IDs
+@section chown and chgrp: Disambiguating user names and IDs
+@cindex user names, disambiguating
+@cindex user IDs, disambiguating
+@cindex group names, disambiguating
+@cindex group IDs, disambiguating
+@cindex disambiguating group names and IDs
+
+Since the @var{owner} and @var{group} arguments to @command{chown} and
+@command{chgrp} may be specified as names or numeric IDs, there is an
+apparent ambiguity.
+What if a user or group @emph{name} is a string of digits?
+@footnote{Using a number as a user name is common in some environments.}
+Should the command interpret it as a user name or as an ID?
+@acronym{POSIX} requires that @command{chown} and @command{chgrp}
+first attempt to resolve the specified string as a name, and
+only once that fails, then try to interpret it as an ID.
+This is troublesome when you want to specify a numeric ID, say 42,
+and it must work even in a pathological situation where
+@samp{42} is a user name that maps to some other user ID, say 1000.
+Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
+1000---not what you intended.
+
+GNU @command{chown} and @command{chgrp} provide a way to work around this,
+that at the same time may result in a significant performance improvement
+by eliminating a database look-up.
+Simply precede each numeric user ID and/or group ID with a @samp{+},
+in order to force its interpretation as an integer:
+
+@example
+chown +42 F
+chgrp +$numeric_group_id another-file
+chown +0:+0 /
+@end example
+
+GNU @command{chown} and @command{chgrp}
+skip the name look-up process for each @samp{+}-prefixed string,
+because a string containing @samp{+} is never a valid user or group name.
+This syntax is accepted on most common Unix systems, but not on Solaris 10.
+
+@node Random sources
+@section Sources of random data
+
+@cindex random sources
+
+The @command{shuf}, @command{shred}, and @command{sort} commands
+sometimes need random data to do their work. For example, @samp{sort
+-R} must choose a hash function at random, and it needs random data to
+make this selection.
+
+Normally these commands use the device file @file{/dev/urandom} as the
+source of random data. Typically, this device gathers environmental
+noise from device drivers and other sources into an entropy pool, and
+uses the pool to generate random bits. If the pool is short of data,
+the device reuses the internal pool to produce more bits, using a
+cryptographically secure pseudorandom number generator.
+
+@file{/dev/urandom} suffices for most practical uses, but applications
+requiring high-value or long-term protection of private data may
+require an alternate data source like @file{/dev/random} or
+@file{/dev/arandom}. The set of available sources depends on your
+operating system.
+
+To use such a source, specify the @option{--random-source=@var{file}}
+option, e.g., @samp{shuf --random-source=/dev/random}. The contents
+of @var{file} should be as random as possible. An error is reported
+if @var{file} does not contain enough bytes to randomize the input
+adequately.
+
+To reproduce the results of an earlier invocation of a command, you
+can save some random data into a file and then use that file as the
+random source in earlier and later invocations of the command.
+
+Some old-fashioned or stripped-down operating systems lack support for
+@command{/dev/urandom}. On these systems commands like @command{shuf}
+by default fall back on an internal pseudorandom generator initialized
+by a small amount of entropy.
+
+@node Target directory
+@section Target directory
+
+@cindex target directory
+
+The @command{cp}, @command{install}, @command{ln}, and @command{mv}
+commands normally treat the last operand specially when it is a
+directory or a symbolic link to a directory. For example, @samp{cp
+source dest} is equivalent to @samp{cp source dest/source} if
+@file{dest} is a directory. Sometimes this behavior is not exactly
+what is wanted, so these commands support the following options to
+allow more fine-grained control:
+
+@table @samp
+
+@item -T
+@itemx --no-target-directory
+@opindex --no-target-directory
+@cindex target directory
+@cindex destination directory
+Do not treat the last operand specially when it is a directory or a
+symbolic link to a directory. This can help avoid race conditions in
+programs that operate in a shared area. For example, when the command
+@samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
+@file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
+renamed to @file{/tmp/dest/source} instead, if some other process
+created @file{/tmp/dest} as a directory. However, if @file{mv
+-T /tmp/source /tmp/dest} succeeds, there is no
+question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
+
+In the opposite situation, where you want the last operand to be
+treated as a directory and want a diagnostic otherwise, you can use
+the @option{--target-directory} (@option{-t}) option.
+
+@item -t @var{directory}
+@itemx @w{@kbd{--target-directory}=@var{directory}}
+@opindex --target-directory
+@cindex target directory
+@cindex destination directory
+Use @var{directory} as the directory component of each destination
+file name.
+
+The interface for most programs is that after processing options and a
+finite (possibly zero) number of fixed-position arguments, the remaining
+argument list is either expected to be empty, or is a list of items
+(usually files) that will all be handled identically. The @command{xargs}
+program is designed to work well with this convention.
+
+The commands in the @command{mv}-family are unusual in that they take
+a variable number of arguments with a special case at the @emph{end}
+(namely, the target directory). This makes it nontrivial to perform some
+operations, e.g., ``move all files from here to ../d/'', because
+@code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
+doesn't have a clean way to specify an extra final argument for each
+invocation of the subject command. (It can be done by going through a
+shell command, but that requires more human labor and brain power than
+it should.)
+
+The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
+@command{install}, @command{ln}, and @command{mv} programs to be used
+conveniently with @command{xargs}. For example, you can move the files
+from the current directory to a sibling directory, @code{d} like this:
+
+@smallexample
+ls | xargs mv -t ../d --
+@end smallexample
+
+However, this doesn't move files whose names begin with @samp{.}.
+If you use the @sc{gnu} @command{find} program, you can move those
+files too, with this command:
+
+@example
+find . -mindepth 1 -maxdepth 1 \
+ | xargs mv -t ../d
+@end example
+
+But both of the above approaches fail if there are no files in the
+current directory, or if any file has a name containing a blank or
+some other special characters.
+The following example removes those limitations and requires both
+@sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
+
+@example
+find . -mindepth 1 -maxdepth 1 -print0 \
+ | xargs --null --no-run-if-empty \
+ mv -t ../d
+@end example
+
+@end table
+
+@noindent
+The @option{--target-directory} (@option{-t}) and
+@option{--no-target-directory} (@option{-T})
+options cannot be combined.
+
+@node Trailing slashes
+@section Trailing slashes
+
+@cindex trailing slashes
+
+Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
+remove any trailing slashes from each @var{source} argument before
+operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
+this behavior.
+
+This is useful when a @var{source} argument may have a trailing slash and
+@c FIXME: mv's behavior in this case is system-dependent
+specify a symbolic link to a directory. This scenario is in fact rather
+common because some shells can automatically append a trailing slash when
+performing file name completion on such symbolic links. Without this
+option, @command{mv}, for example, (via the system's rename function) must
+interpret a trailing slash as a request to dereference the symbolic link
+and so must rename the indirectly referenced @emph{directory} and not
+the symbolic link. Although it may seem surprising that such behavior
+be the default, it is required by @acronym{POSIX} and is consistent with
+other parts of that standard.
+
+@node Traversing symlinks
+@section Traversing symlinks
+
+@cindex symbolic link to directory, controlling traversal of
+
+The following options modify how @command{chown} and @command{chgrp}
+@c FIXME: note that `du' has these options, too, but they have slightly
+@c different meaning.
+traverse a hierarchy when the @option{--recursive} (@option{-R})
+option is also specified.
+If more than one of the following options is specified, only the final
+one takes effect.
+These options specify whether processing a symbolic link to a directory
+entails operating on just the symbolic link or on all files in the
+hierarchy rooted at that directory.
+
+These options are independent of @option{--dereference} and
+@option{--no-dereference} (@option{-h}), which control whether to modify
+a symlink or its referent.
+
+@table @samp
+
+@macro choptH
+@item -H
+@opindex -H
+@cindex symbolic link to directory, traverse each that is specified on the command line
+If @option{--recursive} (@option{-R}) is specified and
+a command line argument is a symbolic link to a directory, traverse it.
+@end macro
+@choptH
+
+@macro choptL
+@item -L
+@opindex -L
+@cindex symbolic link to directory, traverse each that is encountered
+In a recursive traversal, traverse every symbolic link to a directory
+that is encountered.
+@end macro
+@choptL
+
+@macro choptP
+@item -P
+@opindex -P
+@cindex symbolic link to directory, never traverse
+Do not traverse any symbolic links.
+This is the default if none of @option{-H}, @option{-L},
+or @option{-P} is specified.
+@end macro
+@choptP
+
+@end table
+
+
+@node Treating / specially
+@section Treating @file{/} specially
+
+Certain commands can operate destructively on entire hierarchies.
+For example, if a user with appropriate privileges mistakenly runs
+@samp{rm -rf / tmp/junk}, that may remove
+all files on the entire system. Since there are so few
+legitimate uses for such a command,
+@sc{gnu} @command{rm} normally declines to operate on any directory
+that resolves to @file{/}. If you really want to try to remove all
+the files on your system, you can use the @option{--no-preserve-root}
+option, but the default behavior, specified by the
+@option{--preserve-option}, is safer for most purposes.
+
+The commands @command{chgrp}, @command{chmod} and @command{chown}
+can also operate destructively on entire hierarchies, so they too
+support these options. Although, unlike @command{rm}, they don't
+actually unlink files, these commands are arguably more dangerous
+when operating recursively on @file{/}, since they often work much
+more quickly, and hence damage more files before an alert user can
+interrupt them. Tradition and @acronym{POSIX} require these commands
+to operate recursively on @file{/}, so they default to
+@option{--no-preserve-root}, but using the @option{--preserve-root}
+option makes them safer for most purposes. For convenience you can
+specify @option{--preserve-root} in an alias or in a shell function.
+
+Note that the @option{--preserve-root} option also ensures
+that @command{chgrp} and @command{chown} do not modify @file{/}
+even when dereferencing a symlink pointing to @file{/}.
+
+@node Special built-in utilities
+@section Special built-in utilities
+
+Some programs like @command{nice} can invoke other programs; for
+example, the command @samp{nice cat file} invokes the program
+@command{cat} by executing the command @samp{cat file}. However,
+@dfn{special built-in utilities} like @command{exit} cannot be invoked
+this way. For example, the command @samp{nice exit} does not have a
+well-defined behavior: it may generate an error message instead of
+exiting.
+
+Here is a list of the special built-in utilities that are standardized
+by @acronym{POSIX} 1003.1-2004.
+
+@quotation
+@t{.@: : break continue eval exec exit export readonly
+return set shift times trap unset}
+@end quotation
+
+For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
+the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
+pwd} do not work as you might expect.
+
+Many shells extend this list. For example, Bash has several extra
+special built-in utilities like @command{history}, and
+@command{suspend}, and with Bash the command @samp{nice suspend}
+generates an error message instead of suspending.
+
+@node Standards conformance
+@section Standards conformance
+
+@vindex POSIXLY_CORRECT
+In a few cases, the @sc{gnu} utilities' default behavior is
+incompatible with the @acronym{POSIX} standard. To suppress these
+incompatibilities, define the @env{POSIXLY_CORRECT} environment
+variable. Unless you are checking for @acronym{POSIX} conformance, you
+probably do not need to define @env{POSIXLY_CORRECT}.
+
+Newer versions of @acronym{POSIX} are occasionally incompatible with older
+versions. For example, older versions of @acronym{POSIX} required the
+command @samp{sort +1} to sort based on the second and succeeding
+fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
+the same command is required to sort the file named @file{+1}, and you
+must instead use the command @samp{sort -k 2} to get the field-based
+sort.
+
+@vindex _POSIX2_VERSION
+The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
+that is standard for your system. To cause them to conform to a
+different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
+environment variable to a value of the form @var{yyyymm} specifying
+the year and month the standard was adopted. Two values are currently
+supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
+@acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
+1003.1-2001. For example, if you have a newer system but are running software
+that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
+or @samp{tail +10}, you can work around any compatibility problems by setting
+@samp{_POSIX2_VERSION=199209} in your environment.
+
+@node Output of entire files
+@chapter Output of entire files
+
+@cindex output of entire files
+@cindex entire files, output of
+
+These commands read and write entire files, possibly transforming them
+in some way.
+
+@menu
+* cat invocation:: Concatenate and write files.
+* tac invocation:: Concatenate and write files in reverse.
+* nl invocation:: Number lines and write files.
+* od invocation:: Write files in octal or other formats.
+* base64 invocation:: Transform data into printable data.
+@end menu
+
+@node cat invocation
+@section @command{cat}: Concatenate and write files
+
+@pindex cat
+@cindex concatenate and write files
+@cindex copying files
+
+@command{cat} copies each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output. Synopsis:
+
+@example
+cat [@var{option}] [@var{file}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -A
+@itemx --show-all
+@opindex -A
+@opindex --show-all
+Equivalent to @option{-vET}.
+
+@item -b
+@itemx --number-nonblank
+@opindex -b
+@opindex --number-nonblank
+Number all nonempty output lines, starting with 1.
+
+@item -e
+@opindex -e
+Equivalent to @option{-vE}.
+
+@item -E
+@itemx --show-ends
+@opindex -E
+@opindex --show-ends
+Display a @samp{$} after the end of each line.
+
+@item -n
+@itemx --number
+@opindex -n
+@opindex --number
+Number all output lines, starting with 1.
+
+@item -s
+@itemx --squeeze-blank
+@opindex -s
+@opindex --squeeze-blank
+@cindex squeezing empty lines
+Suppress repeated adjacent empty lines; output just one empty line
+instead of several.
+
+@item -t
+@opindex -t
+Equivalent to @option{-vT}.
+
+@item -T
+@itemx --show-tabs
+@opindex -T
+@opindex --show-tabs
+Display TAB characters as @samp{^I}.
+
+@item -u
+@opindex -u
+Ignored; for @acronym{POSIX} compatibility.
+
+@item -v
+@itemx --show-nonprinting
+@opindex -v
+@opindex --show-nonprinting
+Display control characters except for LFD and TAB using
+@samp{^} notation and precede characters that have the high bit set with
+@samp{M-}.
+
+@end table
+
+On systems like MS-DOS that distinguish between text and binary files,
+@command{cat} normally reads and writes in binary mode. However,
+@command{cat} reads in text mode if one of the options
+@option{-bensAE} is used or if @command{cat} is reading from standard
+input and standard input is a terminal. Similarly, @command{cat}
+writes in text mode if one of the options @option{-bensAE} is used or
+if standard output is a terminal.
+
+@exitstatus
+
+Examples:
+
+@smallexample
+# Output f's contents, then standard input, then g's contents.
+cat f - g
+
+# Copy standard input to standard output.
+cat
+@end smallexample
+
+
+@node tac invocation
+@section @command{tac}: Concatenate and write files in reverse
+
+@pindex tac
+@cindex reversing files
+
+@command{tac} copies each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, reversing the
+records (lines by default) in each separately. Synopsis:
+
+@example
+tac [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@dfn{Records} are separated by instances of a string (newline by
+default). By default, this separator string is attached to the end of
+the record that it follows in the file.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --before
+@opindex -b
+@opindex --before
+The separator is attached to the beginning of the record that it
+precedes in the file.
+
+@item -r
+@itemx --regex
+@opindex -r
+@opindex --regex
+Treat the separator string as a regular expression. Users of @command{tac}
+on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
+binary mode, each line of a text file might end with a CR/LF pair
+instead of the Unix-style LF.
+
+@item -s @var{separator}
+@itemx --separator=@var{separator}
+@opindex -s
+@opindex --separator
+Use @var{separator} as the record separator, instead of newline.
+
+@end table
+
+@exitstatus
+
+
+@node nl invocation
+@section @command{nl}: Number lines and write files
+
+@pindex nl
+@cindex numbering lines
+@cindex line numbering
+
+@command{nl} writes each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, with line numbers
+added to some or all of the lines. Synopsis:
+
+@example
+nl [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex logical pages, numbering on
+@command{nl} decomposes its input into (logical) pages; by default, the
+line number is reset to 1 at the top of each logical page. @command{nl}
+treats all of the input files as a single document; it does not reset
+line numbers or logical pages between files.
+
+@cindex headers, numbering
+@cindex body, numbering
+@cindex footers, numbering
+A logical page consists of three sections: header, body, and footer.
+Any of the sections can be empty. Each can be numbered in a different
+style from the others.
+
+The beginnings of the sections of logical pages are indicated in the
+input file by a line containing exactly one of these delimiter strings:
+
+@table @samp
+@item \:\:\:
+start of header;
+@item \:\:
+start of body;
+@item \:
+start of footer.
+@end table
+
+The two characters from which these strings are made can be changed from
+@samp{\} and @samp{:} via options (see below), but the pattern and
+length of each string cannot be changed.
+
+A section delimiter is replaced by an empty line on output. Any text
+that comes before the first section delimiter string in the input file
+is considered to be part of a body section, so @command{nl} treats a
+file that contains no section delimiters as a single body section.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b @var{style}
+@itemx --body-numbering=@var{style}
+@opindex -b
+@opindex --body-numbering
+Select the numbering style for lines in the body section of each
+logical page. When a line is not numbered, the current line number
+is not incremented, but the line number separator character is still
+prepended to the line. The styles are:
+
+@table @samp
+@item a
+number all lines,
+@item t
+number only nonempty lines (default for body),
+@item n
+do not number lines (default for header and footer),
+@item p@var{bre}
+number only lines that contain a match for the basic regular
+expression @var{bre}.
+@xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
+@end table
+
+@item -d @var{cd}
+@itemx --section-delimiter=@var{cd}
+@opindex -d
+@opindex --section-delimiter
+@cindex section delimiters of pages
+Set the section delimiter characters to @var{cd}; default is
+@samp{\:}. If only @var{c} is given, the second remains @samp{:}.
+(Remember to protect @samp{\} or other metacharacters from shell
+expansion with quotes or extra backslashes.)
+
+@item -f @var{style}
+@itemx --footer-numbering=@var{style}
+@opindex -f
+@opindex --footer-numbering
+Analogous to @option{--body-numbering}.
+
+@item -h @var{style}
+@itemx --header-numbering=@var{style}
+@opindex -h
+@opindex --header-numbering
+Analogous to @option{--body-numbering}.
+
+@item -i @var{number}
+@itemx --page-increment=@var{number}
+@opindex -i
+@opindex --page-increment
+Increment line numbers by @var{number} (default 1).
+
+@item -l @var{number}
+@itemx --join-blank-lines=@var{number}
+@opindex -l
+@opindex --join-blank-lines
+@cindex empty lines, numbering
+@cindex blank lines, numbering
+Consider @var{number} (default 1) consecutive empty lines to be one
+logical line for numbering, and only number the last one. Where fewer
+than @var{number} consecutive empty lines occur, do not number them.
+An empty line is one that contains no characters, not even spaces
+or tabs.
+
+@item -n @var{format}
+@itemx --number-format=@var{format}
+@opindex -n
+@opindex --number-format
+Select the line numbering format (default is @code{rn}):
+
+@table @samp
+@item ln
+@opindex ln @r{format for @command{nl}}
+left justified, no leading zeros;
+@item rn
+@opindex rn @r{format for @command{nl}}
+right justified, no leading zeros;
+@item rz
+@opindex rz @r{format for @command{nl}}
+right justified, leading zeros.
+@end table
+
+@item -p
+@itemx --no-renumber
+@opindex -p
+@opindex --no-renumber
+Do not reset the line number at the start of a logical page.
+
+@item -s @var{string}
+@itemx --number-separator=@var{string}
+@opindex -s
+@opindex --number-separator
+Separate the line number from the text line in the output with
+@var{string} (default is the TAB character).
+
+@item -v @var{number}
+@itemx --starting-line-number=@var{number}
+@opindex -v
+@opindex --starting-line-number
+Set the initial line number on each logical page to @var{number} (default 1).
+
+@item -w @var{number}
+@itemx --number-width=@var{number}
+@opindex -w
+@opindex --number-width
+Use @var{number} characters for line numbers (default 6).
+
+@end table
+
+@exitstatus
+
+
+@node od invocation
+@section @command{od}: Write files in octal or other formats
+
+@pindex od
+@cindex octal dump of files
+@cindex hex dump of files
+@cindex ASCII dump of files
+@cindex file contents, dumping unambiguously
+
+@command{od} writes an unambiguous representation of each @var{file}
+(@samp{-} means standard input), or standard input if none are given.
+Synopses:
+
+@smallexample
+od [@var{option}]@dots{} [@var{file}]@dots{}
+od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
+od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
+@end smallexample
+
+Each line of output consists of the offset in the input, followed by
+groups of data from the file. By default, @command{od} prints the offset in
+octal, and each group of file data is a C @code{short int}'s worth of input
+printed as a single octal number.
+
+If @var{offset} is given, it specifies how many input bytes to skip
+before formatting and writing. By default, it is interpreted as an
+octal number, but the optional trailing decimal point causes it to be
+interpreted as decimal. If no decimal is specified and the offset
+begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
+number. If there is a trailing @samp{b}, the number of bytes skipped
+will be @var{offset} multiplied by 512.
+
+If a command is of both the first and second forms, the second form is
+assumed if the last operand begins with @samp{+} or (if there are two
+operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
+the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
+file name.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -A @var{radix}
+@itemx --address-radix=@var{radix}
+@opindex -A
+@opindex --address-radix
+@cindex radix for file offsets
+@cindex file offset radix
+Select the base in which file offsets are printed. @var{radix} can
+be one of the following:
+
+@table @samp
+@item d
+decimal;
+@item o
+octal;
+@item x
+hexadecimal;
+@item n
+none (do not print offsets).
+@end table
+
+The default is octal.
+
+@item -j @var{bytes}
+@itemx --skip-bytes=@var{bytes}
+@opindex -j
+@opindex --skip-bytes
+Skip @var{bytes} input bytes before formatting and writing. If
+@var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
+hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
+in decimal.
+@multiplierSuffixes{bytes}
+
+@item -N @var{bytes}
+@itemx --read-bytes=@var{bytes}
+@opindex -N
+@opindex --read-bytes
+Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
+@code{bytes} are interpreted as for the @option{-j} option.
+
+@item -S @var{bytes}
+@itemx --strings[=@var{bytes}]
+@opindex -S
+@opindex --strings
+@cindex string constants, outputting
+Instead of the normal output, output only @dfn{string constants}: at
+least @var{bytes} consecutive @acronym{ASCII} graphic characters,
+followed by a zero byte (@acronym{ASCII} @sc{nul}).
+Prefixes and suffixes on @code{bytes} are interpreted as for the
+@option{-j} option.
+
+If @var{n} is omitted with @option{--strings}, the default is 3.
+
+@item -t @var{type}
+@itemx --format=@var{type}
+@opindex -t
+@opindex --format
+Select the format in which to output the file data. @var{type} is a
+string of one or more of the below type indicator characters. If you
+include more than one type indicator character in a single @var{type}
+string, or use this option more than once, @command{od} writes one copy
+of each output line using each of the data types that you specified,
+in the order that you specified.
+
+Adding a trailing ``z'' to any type specification appends a display
+of the @acronym{ASCII} character representation of the printable characters
+to the output line generated by the type specification.
+
+@table @samp
+@item a
+named character, ignoring high-order bit
+@item c
+@acronym{ASCII} character or backslash escape,
+@item d
+signed decimal
+@item f
+floating point
+@item o
+octal
+@item u
+unsigned decimal
+@item x
+hexadecimal
+@end table
+
+The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
+newline, and @samp{nul} for a zero byte. Only the least significant
+seven bits of each byte is used; the high-order bit is ignored.
+Type @code{c} outputs
+@samp{ }, @samp{\n}, and @code{\0}, respectively.
+
+@cindex type size
+Except for types @samp{a} and @samp{c}, you can specify the number
+of bytes to use in interpreting each number in the given data type
+by following the type indicator character with a decimal integer.
+Alternately, you can specify the size of one of the C compiler's
+built-in data types by following the type indicator character with
+one of the following characters. For integers (@samp{d}, @samp{o},
+@samp{u}, @samp{x}):
+
+@table @samp
+@item C
+char
+@item S
+short
+@item I
+int
+@item L
+long
+@end table
+
+For floating point (@code{f}):
+
+@table @asis
+@item F
+float
+@item D
+double
+@item L
+long double
+@end table
+
+@item -v
+@itemx --output-duplicates
+@opindex -v
+@opindex --output-duplicates
+Output consecutive lines that are identical. By default, when two or
+more consecutive output lines would be identical, @command{od} outputs only
+the first line, and puts just an asterisk on the following line to
+indicate the elision.
+
+@item -w[@var{n}]
+@itemx --width[=@var{n}]
+@opindex -w
+@opindex --width
+Dump @code{n} input bytes per output line. This must be a multiple of
+the least common multiple of the sizes associated with the specified
+output types.
+
+If this option is not given at all, the default is 16. If @var{n} is
+omitted, the default is 32.
+
+@end table
+
+The next several options are shorthands for format specifications.
+@sc{gnu} @command{od} accepts any combination of shorthands and format
+specification options. These options accumulate.
+
+@table @samp
+
+@item -a
+@opindex -a
+Output as named characters. Equivalent to @samp{-t a}.
+
+@item -b
+@opindex -b
+Output as octal bytes. Equivalent to @samp{-t o1}.
+
+@item -c
+@opindex -c
+Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
+@samp{-t c}.
+
+@item -d
+@opindex -d
+Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
+
+@item -f
+@opindex -f
+Output as floats. Equivalent to @samp{-t fF}.
+
+@item -i
+@opindex -i
+Output as decimal ints. Equivalent to @samp{-t dI}.
+
+@item -l
+@opindex -l
+Output as decimal long ints. Equivalent to @samp{-t dL}.
+
+@item -o
+@opindex -o
+Output as octal two-byte units. Equivalent to @option{-t o2}.
+
+@item -s
+@opindex -s
+Output as decimal two-byte units. Equivalent to @option{-t d2}.
+
+@item -x
+@opindex -x
+Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
+
+@item --traditional
+@opindex --traditional
+Recognize the non-option label argument that traditional @command{od}
+accepted. The following syntax:
+
+@smallexample
+od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
+@end smallexample
+
+@noindent
+can be used to specify at most one file and optional arguments
+specifying an offset and a pseudo-start address, @var{label}.
+The @var{label} argument is interpreted
+just like @var{offset}, but it specifies an initial pseudo-address. The
+pseudo-addresses are displayed in parentheses following any normal
+address.
+
+@end table
+
+@exitstatus
+
+@node base64 invocation
+@section @command{base64}: Transform data into printable data.
+
+@pindex base64
+@cindex base64 encoding
+
+@command{base64} transforms data read from a file, or standard input,
+into (or from) base64 encoded form. The base64 encoded form uses
+printable @acronym{ASCII} characters to represent binary data.
+Synopses:
+
+@smallexample
+base64 [@var{option}]@dots{} [@var{file}]
+base64 --decode [@var{option}]@dots{} [@var{file}]
+@end smallexample
+
+The base64 encoding expands data to roughly 133% of the original.
+The format conforms to
+@uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -w @var{cols}
+@itemx --wrap=@var{cols}
+@opindex -w
+@opindex --wrap
+@cindex wrap data
+@cindex column to wrap data after
+During encoding, wrap lines after @var{cols} characters. This must be
+a positive number.
+
+The default is to wrap after 76 characters. Use the value 0 to
+disable line wrapping altogether.
+
+@item -d
+@itemx --decode
+@opindex -d
+@opindex --decode
+@cindex Decode base64 data
+@cindex Base64 decoding
+Change the mode of operation, from the default of encoding data, to
+decoding data. Input is expected to be base64 encoded data, and the
+output will be the original data.
+
+@item -i
+@itemx --ignore-garbage
+@opindex -i
+@opindex --ignore-garbage
+@cindex Ignore garbage in base64 stream
+When decoding, newlines are always accepted.
+During decoding, ignore unrecognized bytes,
+to permit distorted data to be decoded.
+
+@end table
+
+@exitstatus
+
+
+@node Formatting file contents
+@chapter Formatting file contents
+
+@cindex formatting file contents
+
+These commands reformat the contents of files.
+
+@menu
+* fmt invocation:: Reformat paragraph text.
+* pr invocation:: Paginate or columnate files for printing.
+* fold invocation:: Wrap input lines to fit in specified width.
+@end menu
+
+
+@node fmt invocation
+@section @command{fmt}: Reformat paragraph text
+
+@pindex fmt
+@cindex reformatting paragraph text
+@cindex paragraphs, reformatting
+@cindex text, reformatting
+
+@command{fmt} fills and joins lines to produce output lines of (at most)
+a given number of characters (75 by default). Synopsis:
+
+@example
+fmt [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@command{fmt} reads from the specified @var{file} arguments (or standard
+input if none are given), and writes to standard output.
+
+By default, blank lines, spaces between words, and indentation are
+preserved in the output; successive input lines with different
+indentation are not joined; tabs are expanded on input and introduced on
+output.
+
+@cindex line-breaking
+@cindex sentences and line-breaking
+@cindex Knuth, Donald E.
+@cindex Plass, Michael F.
+@command{fmt} prefers breaking lines at the end of a sentence, and tries to
+avoid line breaks after the first word of a sentence or before the last
+word of a sentence. A @dfn{sentence break} is defined as either the end
+of a paragraph or a word ending in any of @samp{.?!}, followed by two
+spaces or end of line, ignoring any intervening parentheses or quotes.
+Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
+breaks; the algorithm is a variant of that given by Donald E. Knuth
+and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
+@cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
+1119--1184.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -C
+@itemx --compare
+@opindex -C
+@opindex --compare
+Compare each pair of source and destination files, and if the destination has
+identical content and any specified owner, group, permissions, and possibly
+SELinux context, then do not modify the destination at all.
+
+@item -c
+@itemx --crown-margin
+@opindex -c
+@opindex --crown-margin
+@cindex crown margin
+@dfn{Crown margin} mode: preserve the indentation of the first two
+lines within a paragraph, and align the left margin of each subsequent
+line with that of the second line.
+
+@item -t
+@itemx --tagged-paragraph
+@opindex -t
+@opindex --tagged-paragraph
+@cindex tagged paragraphs
+@dfn{Tagged paragraph} mode: like crown margin mode, except that if
+indentation of the first line of a paragraph is the same as the
+indentation of the second, the first line is treated as a one-line
+paragraph.
+
+@item -s
+@itemx --split-only
+@opindex -s
+@opindex --split-only
+Split lines only. Do not join short lines to form longer ones. This
+prevents sample lines of code, and other such ``formatted'' text from
+being unduly combined.
+
+@item -u
+@itemx --uniform-spacing
+@opindex -u
+@opindex --uniform-spacing
+Uniform spacing. Reduce spacing between words to one space, and spacing
+between sentences to two spaces.
+
+@item -@var{width}
+@itemx -w @var{width}
+@itemx --width=@var{width}
+@opindex -@var{width}
+@opindex -w
+@opindex --width
+Fill output lines up to @var{width} characters (default 75). @command{fmt}
+initially tries to make lines about 7% shorter than this, to give it
+room to balance line lengths.
+
+@item -p @var{prefix}
+@itemx --prefix=@var{prefix}
+Only lines beginning with @var{prefix} (possibly preceded by whitespace)
+are subject to formatting. The prefix and any preceding whitespace are
+stripped for the formatting and then re-attached to each formatted output
+line. One use is to format certain kinds of program comments, while
+leaving the code unchanged.
+
+@end table
+
+@exitstatus
+
+
+@node pr invocation
+@section @command{pr}: Paginate or columnate files for printing
+
+@pindex pr
+@cindex printing, preparing files for
+@cindex multicolumn output, generating
+@cindex merging files in parallel
+
+@command{pr} writes each @var{file} (@samp{-} means standard input), or
+standard input if none are given, to standard output, paginating and
+optionally outputting in multicolumn format; optionally merges all
+@var{file}s, printing all in parallel, one per column. Synopsis:
+
+@example
+pr [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@vindex LC_MESSAGES
+By default, a 5-line header is printed at each page: two blank lines;
+a line with the date, the file name, and the page count; and two more
+blank lines. A footer of five blank lines is also printed.
+The default @var{page_length} is 66
+lines. The default number of text lines is therefore 56.
+The text line of the header takes the form
+@samp{@var{date} @var{string} @var{page}}, with spaces inserted around
+@var{string} so that the line takes up the full @var{page_width}. Here,
+@var{date} is the date (see the @option{-D} or @option{--date-format}
+option for details), @var{string} is the centered header string, and
+@var{page} identifies the page number. The @env{LC_MESSAGES} locale
+category affects the spelling of @var{page}; in the default C locale, it
+is @samp{Page @var{number}} where @var{number} is the decimal page
+number.
+
+Form feeds in the input cause page breaks in the output. Multiple form
+feeds produce empty pages.
+
+Columns are of equal width, separated by an optional string (default
+is @samp{space}). For multicolumn output, lines will always be truncated to
+@var{page_width} (default 72), unless you use the @option{-J} option.
+For single
+column output no line truncation occurs by default. Use @option{-W} option to
+truncate lines in that case.
+
+The following changes were made in version 1.22i and apply to later
+versions of @command{pr}:
+@c FIXME: this whole section here sounds very awkward to me. I
+@c made a few small changes, but really it all needs to be redone. - Brian
+@c OK, I fixed another sentence or two, but some of it I just don't understand.
+@ - Brian
+@itemize @bullet
+
+@item
+Some small @var{letter options} (@option{-s}, @option{-w}) have been
+redefined for better @acronym{POSIX} compliance. The output of some further
+cases has been adapted to other Unix systems. These changes are not
+compatible with earlier versions of the program.
+
+@item
+Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
+have been introduced to turn off unexpected interferences of small letter
+options. The @option{-N} option and the second argument @var{last_page}
+of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
+form feeds set in the input files requires the @option{-T} option.
+
+@item
+Capital letter options override small letter ones.
+
+@item
+Some of the option-arguments (compare @option{-s}, @option{-e},
+@option{-i}, @option{-n}) cannot be specified as separate arguments from the
+preceding option letter (already stated in the @acronym{POSIX} specification).
+@end itemize
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item +@var{first_page}[:@var{last_page}]
+@itemx --pages=@var{first_page}[:@var{last_page}]
+@c The two following @opindex lines evoke warnings because they contain `:'
+@c The `info' spec does not permit that. If we use those lines, we end
+@c up with truncated index entries that don't work.
+@c @opindex +@var{first_page}[:@var{last_page}]
+@c @opindex --pages=@var{first_page}[:@var{last_page}]
+@opindex +@var{page_range}
+@opindex --pages=@var{page_range}
+Begin printing with page @var{first_page} and stop with @var{last_page}.
+Missing @samp{:@var{last_page}} implies end of file. While estimating
+the number of skipped pages each form feed in the input file results
+in a new page. Page counting with and without @samp{+@var{first_page}}
+is identical. By default, counting starts with the first page of input
+file (not first page printed). Line numbering may be altered by @option{-N}
+option.
+
+@item -@var{column}
+@itemx --columns=@var{column}
+@opindex -@var{column}
+@opindex --columns
+@cindex down columns
+With each single @var{file}, produce @var{column} columns of output
+(default is 1) and print columns down, unless @option{-a} is used. The
+column width is automatically decreased as @var{column} increases; unless
+you use the @option{-W/-w} option to increase @var{page_width} as well.
+This option might well cause some lines to be truncated. The number of
+lines in the columns on each page are balanced. The options @option{-e}
+and @option{-i} are on for multiple text-column output. Together with
+@option{-J} option column alignment and line truncation is turned off.
+Lines of full length are joined in a free field format and @option{-S}
+option may set field separators. @option{-@var{column}} may not be used
+with @option{-m} option.
+
+@item -a
+@itemx --across
+@opindex -a
+@opindex --across
+@cindex across columns
+With each single @var{file}, print columns across rather than down. The
+@option{-@var{column}} option must be given with @var{column} greater than one.
+If a line is too long to fit in a column, it is truncated.
+
+@item -c
+@itemx --show-control-chars
+@opindex -c
+@opindex --show-control-chars
+Print control characters using hat notation (e.g., @samp{^G}); print
+other nonprinting characters in octal backslash notation. By default,
+nonprinting characters are not changed.
+
+@item -d
+@itemx --double-space
+@opindex -d
+@opindex --double-space
+@cindex double spacing
+Double space the output.
+
+@item -D @var{format}
+@itemx --date-format=@var{format}
+@cindex time formats
+@cindex formatting times
+Format header dates using @var{format}, using the same conventions as
+for the command @samp{date +@var{format}}; @xref{date invocation}.
+Except for directives, which start with
+@samp{%}, characters in @var{format} are printed unchanged. You can use
+this option to specify an arbitrary string in place of the header date,
+e.g., @option{--date-format="Monday morning"}.
+
+@vindex POSIXLY_CORRECT
+@vindex LC_TIME
+The default date format is @samp{%Y-%m-%d %H:%M} (for example,
+@samp{2001-12-04 23:59});
+but if the @env{POSIXLY_CORRECT} environment variable is set
+and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
+locale, the default is @samp{%b %e %H:%M %Y} (for example,
+@samp{Dec@ @ 4 23:59 2001}.
+
+@vindex TZ
+Time stamps are listed according to the time zone rules specified by
+the @env{TZ} environment variable, or by the system default rules if
+@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
+with @env{TZ}, libc, The GNU C Library Reference Manual}.
+
+@item -e[@var{in-tabchar}[@var{in-tabwidth}]]
+@itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
+@opindex -e
+@opindex --expand-tabs
+@cindex input tabs
+Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
+the input tab character (default is the TAB character). Second optional
+argument @var{in-tabwidth} is the input tab character's width (default
+is 8).
+
+@item -f
+@itemx -F
+@itemx --form-feed
+@opindex -F
+@opindex -f
+@opindex --form-feed
+Use a form feed instead of newlines to separate output pages. This does
+not alter the default page length of 66 lines.
+
+@item -h @var{header}
+@itemx --header=@var{header}
+@opindex -h
+@opindex --header
+Replace the file name in the header with the centered string @var{header}.
+When using the shell, @var{header} should be quoted and should be
+separated from @option{-h} by a space.
+
+@item -i[@var{out-tabchar}[@var{out-tabwidth}]]
+@itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
+@opindex -i
+@opindex --output-tabs
+@cindex output tabs
+Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
+is the output tab character (default is the TAB character). Second optional
+argument @var{out-tabwidth} is the output tab character's width (default
+is 8).
+
+@item -J
+@itemx --join-lines
+@opindex -J
+@opindex --join-lines
+Merge lines of full length. Used together with the column options
+@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
+@option{-W/-w} line truncation;
+no column alignment used; may be used with
+@option{--sep-string[=@var{string}]}. @option{-J} has been introduced
+(together with @option{-W} and @option{--sep-string})
+to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
+@option{-s} along with the three column options.
+
+
+@item -l @var{page_length}
+@itemx --length=@var{page_length}
+@opindex -l
+@opindex --length
+Set the page length to @var{page_length} (default 66) lines, including
+the lines of the header [and the footer]. If @var{page_length} is less
+than or equal to 10, the header and footer are omitted, as if the
+@option{-t} option had been given.
+
+@item -m
+@itemx --merge
+@opindex -m
+@opindex --merge
+Merge and print all @var{file}s in parallel, one in each column. If a
+line is too long to fit in a column, it is truncated, unless the @option{-J}
+option is used. @option{--sep-string[=@var{string}]} may be used.
+Empty pages in
+some @var{file}s (form feeds set) produce empty columns, still marked
+by @var{string}. The result is a continuous line numbering and column
+marking throughout the whole merged file. Completely empty merged pages
+show no separators or line numbers. The default header becomes
+@samp{@var{date} @var{page}} with spaces inserted in the middle; this
+may be used with the @option{-h} or @option{--header} option to fill up
+the middle blank part.
+
+@item -n[@var{number-separator}[@var{digits}]]
+@itemx --number-lines[=@var{number-separator}[@var{digits}]]
+@opindex -n
+@opindex --number-lines
+Provide @var{digits} digit line numbering (default for @var{digits} is
+5). With multicolumn output the number occupies the first @var{digits}
+column positions of each text column or only each line of @option{-m}
+output. With single column output the number precedes each line just as
+@option{-m} does. Default counting of the line numbers starts with the
+first line of the input file (not the first line printed, compare the
+@option{--page} option and @option{-N} option).
+Optional argument @var{number-separator} is the character appended to
+the line number to separate it from the text followed. The default
+separator is the TAB character. In a strict sense a TAB is always
+printed with single column output only. The TAB width varies
+with the TAB position, e.g., with the left @var{margin} specified
+by @option{-o} option. With multicolumn output priority is given to
+@samp{equal width of output columns} (a @acronym{POSIX} specification).
+The TAB width is fixed to the value of the first column and does
+not change with different values of left @var{margin}. That means a
+fixed number of spaces is always printed in the place of the
+@var{number-separator} TAB. The tabification depends upon the output
+position.
+
+@item -N @var{line_number}
+@itemx --first-line-number=@var{line_number}
+@opindex -N
+@opindex --first-line-number
+Start line counting with the number @var{line_number} at first line of
+first page printed (in most cases not the first line of the input file).
+
+@item -o @var{margin}
+@itemx --indent=@var{margin}
+@opindex -o
+@opindex --indent
+@cindex indenting lines
+@cindex left margin
+Indent each line with a margin @var{margin} spaces wide (default is zero).
+The total page width is the size of the margin plus the @var{page_width}
+set with the @option{-W/-w} option. A limited overflow may occur with
+numbered single column output (compare @option{-n} option).
+
+@item -r
+@itemx --no-file-warnings
+@opindex -r
+@opindex --no-file-warnings
+Do not print a warning message when an argument @var{file} cannot be
+opened. (The exit status will still be nonzero, however.)
+
+@item -s[@var{char}]
+@itemx --separator[=@var{char}]
+@opindex -s
+@opindex --separator
+Separate columns by a single character @var{char}. The default for
+@var{char} is the TAB character without @option{-w} and @samp{no
+character} with @option{-w}. Without @option{-s} the default separator
+@samp{space} is set. @option{-s[char]} turns off line truncation of all
+three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
+@option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
+
+
+@item -S@var{string}
+@itemx --sep-string[=@var{string}]
+@opindex -S
+@opindex --sep-string
+Use @var{string} to separate output columns. The @option{-S} option doesn't
+affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
+does not affect line truncation or column alignment.
+Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
+separator, TAB@.
+Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
+(same as @option{-S"@w{ }"}). @option{--sep-string} with no
+@samp{=@var{string}} is equivalent to @option{--sep-string=""}.
+
+@item -t
+@itemx --omit-header
+@opindex -t
+@opindex --omit-header
+Do not print the usual header [and footer] on each page, and do not fill
+out the bottom of pages (with blank lines or a form feed). No page
+structure is produced, but form feeds set in the input files are retained.
+The predefined pagination is not changed. @option{-t} or @option{-T} may be
+useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
+in the input file to 4 spaces but don't make any other changes. Use of
+@option{-t} overrides @option{-h}.
+
+@item -T
+@itemx --omit-pagination
+@opindex -T
+@opindex --omit-pagination
+Do not print header [and footer]. In addition eliminate all form feeds
+set in the input files.
+
+@item -v
+@itemx --show-nonprinting
+@opindex -v
+@opindex --show-nonprinting
+Print nonprinting characters in octal backslash notation.
+
+@item -w @var{page_width}
+@itemx --width=@var{page_width}
+@opindex -w
+@opindex --width
+Set page width to @var{page_width} characters for multiple text-column
+output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
+off the default page width and any line truncation and column alignment.
+Lines of full length are merged, regardless of the column options
+set. No @var{page_width} setting is possible with single column output.
+A @acronym{POSIX}-compliant formulation.
+
+@item -W @var{page_width}
+@itemx --page_width=@var{page_width}
+@opindex -W
+@opindex --page_width
+Set the page width to @var{page_width} characters. That's valid with and
+without a column option. Text lines are truncated, unless @option{-J}
+is used. Together with one of the three column options
+(@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
+alignment is always used. The separator options @option{-S} or @option{-s}
+don't affect the @option{-W} option. Default is 72 characters. Without
+@option{-W @var{page_width}} and without any of the column options NO line
+truncation is used (defined to keep downward compatibility and to meet
+most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
+line is never truncated.
+
+@end table
+
+@exitstatus
+
+
+@node fold invocation
+@section @command{fold}: Wrap input lines to fit in specified width
+
+@pindex fold
+@cindex wrapping long input lines
+@cindex folding long input lines
+
+@command{fold} writes each @var{file} (@option{-} means standard input), or
+standard input if none are given, to standard output, breaking long
+lines. Synopsis:
+
+@example
+fold [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @command{fold} breaks lines wider than 80 columns. The output
+is split into as many lines as necessary.
+
+@cindex screen columns
+@command{fold} counts screen columns by default; thus, a tab may count more
+than one column, backspace decreases the column count, and carriage
+return sets the column to zero.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --bytes
+@opindex -b
+@opindex --bytes
+Count bytes rather than columns, so that tabs, backspaces, and carriage
+returns are each counted as taking up one column, just like other
+characters.
+
+@item -s
+@itemx --spaces
+@opindex -s
+@opindex --spaces
+Break at word boundaries: the line is broken after the last blank before
+the maximum line length. If the line contains no such blanks, the line
+is broken at the maximum line length as usual.
+
+@item -w @var{width}
+@itemx --width=@var{width}
+@opindex -w
+@opindex --width
+Use a maximum line length of @var{width} columns instead of 80.
+
+For compatibility @command{fold} supports an obsolete option syntax
+@option{-@var{width}}. New scripts should use @option{-w @var{width}}
+instead.
+
+@end table
+
+@exitstatus
+
+
+@node Output of parts of files
+@chapter Output of parts of files
+
+@cindex output of parts of files
+@cindex parts of files, output of
+
+These commands output pieces of the input.
+
+@menu
+* head invocation:: Output the first part of files.
+* tail invocation:: Output the last part of files.
+* split invocation:: Split a file into fixed-size pieces.
+* csplit invocation:: Split a file into context-determined pieces.
+@end menu
+
+@node head invocation
+@section @command{head}: Output the first part of files
+
+@pindex head
+@cindex initial part of files, outputting
+@cindex first part of files, outputting
+
+@command{head} prints the first part (10 lines by default) of each
+@var{file}; it reads from standard input if no files are given or
+when given a @var{file} of @option{-}. Synopsis:
+
+@example
+head [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+If more than one @var{file} is specified, @command{head} prints a
+one-line header consisting of:
+
+@example
+==> @var{file name} <==
+@end example
+
+@noindent
+before the output for each @var{file}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c @var{n}
+@itemx --bytes=@var{n}
+@opindex -c
+@opindex --bytes
+Print the first @var{n} bytes, instead of initial lines.
+However, if @var{n} starts with a @samp{-},
+print all but the last @var{n} bytes of each file.
+@multiplierSuffixes{n}
+
+@itemx -n @var{n}
+@itemx --lines=@var{n}
+@opindex -n
+@opindex --lines
+Output the first @var{n} lines.
+However, if @var{n} starts with a @samp{-},
+print all but the last @var{n} lines of each file.
+Size multiplier suffixes are the same as with the @option{-c} option.
+
+@item -q
+@itemx --quiet
+@itemx --silent
+@opindex -q
+@opindex --quiet
+@opindex --silent
+Never print file name headers.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Always print file name headers.
+
+@end table
+
+For compatibility @command{head} also supports an obsolete option syntax
+@option{-@var{count}@var{options}}, which is recognized only if it is
+specified first. @var{count} is a decimal number optionally followed
+by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
+@samp{l} to mean count by lines, or other option letters (@samp{cqv}).
+Scripts intended for standard hosts should use @option{-c @var{count}}
+or @option{-n @var{count}} instead. If your script must also run on
+hosts that support only the obsolete syntax, it is usually simpler to
+avoid @command{head}, e.g., by using @samp{sed 5q} instead of
+@samp{head -5}.
+
+@exitstatus
+
+
+@node tail invocation
+@section @command{tail}: Output the last part of files
+
+@pindex tail
+@cindex last part of files, outputting
+
+@command{tail} prints the last part (10 lines by default) of each
+@var{file}; it reads from standard input if no files are given or
+when given a @var{file} of @samp{-}. Synopsis:
+
+@example
+tail [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+If more than one @var{file} is specified, @command{tail} prints a
+one-line header consisting of:
+
+@example
+==> @var{file name} <==
+@end example
+
+@noindent
+before the output for each @var{file}.
+
+@cindex BSD @command{tail}
+@sc{gnu} @command{tail} can output any amount of data (some other versions of
+@command{tail} cannot). It also has no @option{-r} option (print in
+reverse), since reversing a file is really a different job from printing
+the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
+only reverse files that are at most as large as its buffer, which is
+typically 32 KiB@. A more reliable and versatile way to reverse files is
+the @sc{gnu} @command{tac} command.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c @var{n}
+@itemx --bytes=@var{n}
+@opindex -c
+@opindex --bytes
+Output the last @var{n} bytes, instead of final lines.
+However, if @var{n} starts with a @samp{+}, start printing with the
+@var{n}th byte from the start of each file, instead of from the end.
+@multiplierSuffixes{n}
+
+@item -f
+@itemx --follow[=@var{how}]
+@opindex -f
+@opindex --follow
+@cindex growing files
+@vindex name @r{follow option}
+@vindex descriptor @r{follow option}
+Loop forever trying to read more characters at the end of the file,
+presumably because the file is growing.
+If more than one file is given, @command{tail} prints a header whenever it
+gets output from a different file, to indicate which file that output is
+from.
+
+There are two ways to specify how you'd like to track files with this option,
+but that difference is noticeable only when a followed file is removed or
+renamed.
+If you'd like to continue to track the end of a growing file even after
+it has been unlinked, use @option{--follow=descriptor}. This is the default
+behavior, but it is not useful if you're tracking a log file that may be
+rotated (removed or renamed, then reopened). In that case, use
+@option{--follow=name} to track the named file by reopening it periodically
+to see if it has been removed and recreated by some other program.
+
+No matter which method you use, if the tracked file is determined to have
+shrunk, @command{tail} prints a message saying the file has been truncated
+and resumes tracking the end of the file from the newly-determined endpoint.
+
+When a file is removed, @command{tail}'s behavior depends on whether it is
+following the name or the descriptor. When following by name, tail can
+detect that a file has been removed and gives a message to that effect,
+and if @option{--retry} has been specified it will continue checking
+periodically to see if the file reappears.
+When following a descriptor, tail does not detect that the file has
+been unlinked or renamed and issues no message; even though the file
+may no longer be accessible via its original name, it may still be
+growing.
+
+The option values @samp{descriptor} and @samp{name} may be specified only
+with the long form of the option, not with @option{-f}.
+
+@vindex POSIXLY_CORRECT
+If @env{POSIXLY_CORRECT} is set, the @option{-f} option is ignored if
+no @var{file} operand is specified and standard input is a FIFO or a pipe.
+
+@item -F
+@opindex -F
+This option is the same as @option{--follow=name --retry}. That is, tail
+will attempt to reopen a file when it is removed. Should this fail, tail
+will keep trying until it becomes accessible again.
+
+@itemx --retry
+@opindex --retry
+This option is useful mainly when following by name (i.e., with
+@option{--follow=name}).
+Without this option, when tail encounters a file that doesn't
+exist or is otherwise inaccessible, it reports that fact and
+never checks it again.
+
+@itemx --sleep-interval=@var{number}
+@opindex --sleep-interval
+Change the number of seconds to wait between iterations (the default is 1.0).
+During one iteration, every specified file is checked to see if it has
+changed size.
+Historical implementations of @command{tail} have required that
+@var{number} be an integer. However, GNU @command{tail} accepts
+an arbitrary floating point number (using a period before any
+fractional digits).
+
+@itemx --pid=@var{pid}
+@opindex --pid
+When following by name or by descriptor, you may specify the process ID,
+@var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
+after that process terminates, tail will also terminate. This will
+work properly only if the writer and the tailing process are running on
+the same machine. For example, to save the output of a build in a file
+and to watch the file grow, if you invoke @command{make} and @command{tail}
+like this then the tail process will stop when your build completes.
+Without this option, you would have had to kill the @code{tail -f}
+process yourself.
+
+@example
+$ make >& makerr & tail --pid=$! -f makerr
+@end example
+
+If you specify a @var{pid} that is not in use or that does not correspond
+to the process that is writing to the tailed files, then @command{tail}
+may terminate long before any @var{file}s stop growing or it may not
+terminate until long after the real writer has terminated.
+Note that @option{--pid} cannot be supported on some systems; @command{tail}
+will print a warning if this is the case.
+
+@itemx --max-unchanged-stats=@var{n}
+@opindex --max-unchanged-stats
+When tailing a file by name, if there have been @var{n} (default
+n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
+iterations for which the file has not changed, then
+@code{open}/@code{fstat} the file to determine if that file name is
+still associated with the same device/inode-number pair as before.
+When following a log file that is rotated, this is approximately the
+number of seconds between when tail prints the last pre-rotation lines
+and when it prints the lines that have accumulated in the new log file.
+This option is meaningful only when following by name.
+
+@itemx -n @var{n}
+@itemx --lines=@var{n}
+@opindex -n
+@opindex --lines
+Output the last @var{n} lines.
+However, if @var{n} starts with a @samp{+}, start printing with the
+@var{n}th line from the start of each file, instead of from the end.
+Size multiplier suffixes are the same as with the @option{-c} option.
+
+@item -q
+@itemx --quiet
+@itemx --silent
+@opindex -q
+@opindex --quiet
+@opindex --silent
+Never print file name headers.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Always print file name headers.
+
+@end table
+
+For compatibility @command{tail} also supports an obsolete usage
+@samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
+only if it does not conflict with the usage described
+above. This obsolete form uses exactly one option and at most one
+file. In the option, @var{count} is an optional decimal number optionally
+followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
+by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
+which has the same meaning as @option{-f}.
+
+@vindex _POSIX2_VERSION
+On older systems, the leading @samp{-} can be replaced by @samp{+} in
+the obsolete option syntax with the same meaning as in counts, and
+obsolete usage overrides normal usage when the two conflict.
+This obsolete behavior can be enabled or disabled with the
+@env{_POSIX2_VERSION} environment variable (@pxref{Standards
+conformance}).
+
+Scripts intended for use on standard hosts should avoid obsolete
+syntax and should use @option{-c @var{count}[b]}, @option{-n
+@var{count}}, and/or @option{-f} instead. If your script must also
+run on hosts that support only the obsolete syntax, you can often
+rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
+'$p'} rather than @samp{tail -1}. If that's not possible, the script
+can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
+then @dots{}} to decide which syntax to use.
+
+Even if your script assumes the standard behavior, you should still
+beware usages whose behaviors differ depending on the @acronym{POSIX}
+version. For example, avoid @samp{tail - main.c}, since it might be
+interpreted as either @samp{tail main.c} or as @samp{tail -- -
+main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
+-c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
+mean either @samp{tail ./+4} or @samp{tail -n +4}.
+
+@exitstatus
+
+
+@node split invocation
+@section @command{split}: Split a file into fixed-size pieces
+
+@pindex split
+@cindex splitting a file into pieces
+@cindex pieces, splitting a file into
+
+@command{split} creates output files containing consecutive sections of
+@var{input} (standard input if none is given or @var{input} is
+@samp{-}). Synopsis:
+
+@example
+split [@var{option}] [@var{input} [@var{prefix}]]
+@end example
+
+By default, @command{split} puts 1000 lines of @var{input} (or whatever is
+left over for the last section), into each output file.
+
+@cindex output file name prefix
+The output files' names consist of @var{prefix} (@samp{x} by default)
+followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
+default), such that concatenating the output files in traditional
+sorted order by file name produces
+the original input file. If the output file names are exhausted,
+@command{split} reports an error without deleting the output files
+that it did create.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -l @var{lines}
+@itemx --lines=@var{lines}
+@opindex -l
+@opindex --lines
+Put @var{lines} lines of @var{input} into each output file.
+
+For compatibility @command{split} also supports an obsolete
+option syntax @option{-@var{lines}}. New scripts should use @option{-l
+@var{lines}} instead.
+
+@item -b @var{size}
+@itemx --bytes=@var{size}
+@opindex -b
+@opindex --bytes
+Put @var{size} bytes of @var{input} into each output file.
+@multiplierSuffixes{size}
+
+@item -C @var{size}
+@itemx --line-bytes=@var{size}
+@opindex -C
+@opindex --line-bytes
+Put into each output file as many complete lines of @var{input} as
+possible without exceeding @var{size} bytes. Individual lines longer than
+@var{size} bytes are broken into multiple files.
+@var{size} has the same format as for the @option{--bytes} option.
+
+@item -a @var{length}
+@itemx --suffix-length=@var{length}
+@opindex -a
+@opindex --suffix-length
+Use suffixes of length @var{length}. The default @var{length} is 2.
+
+@item -d
+@itemx --numeric-suffixes
+@opindex -d
+@opindex --numeric-suffixes
+Use digits in suffixes rather than lower-case letters.
+
+@itemx --verbose
+@opindex --verbose
+Write a diagnostic just before each output file is opened.
+
+@end table
+
+@exitstatus
+
+
+@node csplit invocation
+@section @command{csplit}: Split a file into context-determined pieces
+
+@pindex csplit
+@cindex context splitting
+@cindex splitting a file into pieces by context
+
+@command{csplit} creates zero or more output files containing sections of
+@var{input} (standard input if @var{input} is @samp{-}). Synopsis:
+
+@example
+csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
+@end example
+
+The contents of the output files are determined by the @var{pattern}
+arguments, as detailed below. An error occurs if a @var{pattern}
+argument refers to a nonexistent line of the input file (e.g., if no
+remaining line matches a given regular expression). After every
+@var{pattern} has been matched, any remaining input is copied into one
+last output file.
+
+By default, @command{csplit} prints the number of bytes written to each
+output file after it has been created.
+
+The types of pattern arguments are:
+
+@table @samp
+
+@item @var{n}
+Create an output file containing the input up to but not including line
+@var{n} (a positive integer). If followed by a repeat count, also
+create an output file containing the next @var{n} lines of the input
+file once for each repeat.
+
+@item /@var{regexp}/[@var{offset}]
+Create an output file containing the current line up to (but not
+including) the next line of the input file that contains a match for
+@var{regexp}. The optional @var{offset} is an integer.
+If it is given, the input up to (but not including) the
+matching line plus or minus @var{offset} is put into the output file,
+and the line after that begins the next section of input.
+
+@item %@var{regexp}%[@var{offset}]
+Like the previous type, except that it does not create an output
+file, so that section of the input file is effectively ignored.
+
+@item @{@var{repeat-count}@}
+Repeat the previous pattern @var{repeat-count} additional
+times. The @var{repeat-count} can either be a positive integer or an
+asterisk, meaning repeat as many times as necessary until the input is
+exhausted.
+
+@end table
+
+The output files' names consist of a prefix (@samp{xx} by default)
+followed by a suffix. By default, the suffix is an ascending sequence
+of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
+concatenating the output files in sorted order by file name produces the
+original input file.
+
+By default, if @command{csplit} encounters an error or receives a hangup,
+interrupt, quit, or terminate signal, it removes any output files
+that it has created so far before it exits.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f @var{prefix}
+@itemx --prefix=@var{prefix}
+@opindex -f
+@opindex --prefix
+@cindex output file name prefix
+Use @var{prefix} as the output file name prefix.
+
+@item -b @var{suffix}
+@itemx --suffix=@var{suffix}
+@opindex -b
+@opindex --suffix
+@cindex output file name suffix
+Use @var{suffix} as the output file name suffix. When this option is
+specified, the suffix string must include exactly one
+@code{printf(3)}-style conversion specification, possibly including
+format specification flags, a field width, a precision specifications,
+or all of these kinds of modifiers. The format letter must convert a
+binary integer argument to readable form; thus, only @samp{d}, @samp{i},
+@samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
+entire @var{suffix} is given (with the current output file number) to
+@code{sprintf(3)} to form the file name suffixes for each of the
+individual output files in turn. If this option is used, the
+@option{--digits} option is ignored.
+
+@item -n @var{digits}
+@itemx --digits=@var{digits}
+@opindex -n
+@opindex --digits
+Use output file names containing numbers that are @var{digits} digits
+long instead of the default 2.
+
+@item -k
+@itemx --keep-files
+@opindex -k
+@opindex --keep-files
+Do not remove output files when errors are encountered.
+
+@item -z
+@itemx --elide-empty-files
+@opindex -z
+@opindex --elide-empty-files
+Suppress the generation of zero-length output files. (In cases where
+the section delimiters of the input file are supposed to mark the first
+lines of each of the sections, the first output file will generally be a
+zero-length file unless you use this option.) The output file sequence
+numbers always run consecutively starting from 0, even when this option
+is specified.
+
+@item -s
+@itemx -q
+@itemx --silent
+@itemx --quiet
+@opindex -s
+@opindex -q
+@opindex --silent
+@opindex --quiet
+Do not print counts of output file sizes.
+
+@end table
+
+@exitstatus
+
+Here is an example of its usage.
+First, create an empty directory for the exercise,
+and cd into it:
+
+@example
+$ mkdir d && cd d
+@end example
+
+Now, split the sequence of 1..14 on lines that end with 0 or 5:
+
+@example
+$ seq 14 | csplit - '/[05]$/' '@{*@}'
+8
+10
+15
+@end example
+
+Each number printed above is the size of an output
+file that csplit has just created.
+List the names of those output files:
+
+@example
+$ ls
+xx00 xx01 xx02
+@end example
+
+Use @command{head} to show their contents:
+
+@example
+$ head xx*
+==> xx00 <==
+1
+2
+3
+4
+
+==> xx01 <==
+5
+6
+7
+8
+9
+
+==> xx02 <==
+10
+11
+12
+13
+14
+@end example
+
+@node Summarizing files
+@chapter Summarizing files
+
+@cindex summarizing files
+
+These commands generate just a few numbers representing entire
+contents of files.
+
+@menu
+* wc invocation:: Print newline, word, and byte counts.
+* sum invocation:: Print checksum and block counts.
+* cksum invocation:: Print CRC checksum and byte counts.
+* md5sum invocation:: Print or check MD5 digests.
+* sha1sum invocation:: Print or check SHA-1 digests.
+* sha2 utilities:: Print or check SHA-2 digests.
+@end menu
+
+
+@node wc invocation
+@section @command{wc}: Print newline, word, and byte counts
+
+@pindex wc
+@cindex byte count
+@cindex character count
+@cindex word count
+@cindex line count
+
+@command{wc} counts the number of bytes, characters, whitespace-separated
+words, and newlines in each given @var{file}, or standard input if none
+are given or for a @var{file} of @samp{-}. Synopsis:
+
+@example
+wc [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex total counts
+@command{wc} prints one line of counts for each file, and if the file was
+given as an argument, it prints the file name following the counts. If
+more than one @var{file} is given, @command{wc} prints a final line
+containing the cumulative counts, with the file name @file{total}. The
+counts are printed in this order: newlines, words, characters, bytes,
+maximum line length.
+Each count is printed right-justified in a field with at least one
+space between fields so that the numbers and file names normally line
+up nicely in columns. The width of the count fields varies depending
+on the inputs, so you should not depend on a particular field width.
+However, as a @acronym{GNU} extension, if only one count is printed,
+it is guaranteed to be printed without leading spaces.
+
+By default, @command{wc} prints three counts: the newline, words, and byte
+counts. Options can specify that only certain counts be printed.
+Options do not undo others previously given, so
+
+@example
+wc --bytes --words
+@end example
+
+@noindent
+prints both the byte counts and the word counts.
+
+With the @option{--max-line-length} option, @command{wc} prints the length
+of the longest line per file, and if there is more than one file it
+prints the maximum (not the sum) of those lengths. The line lengths here
+are measured in screen columns, according to the current locale and
+assuming tab positions in every 8th column.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --bytes
+@opindex -c
+@opindex --bytes
+Print only the byte counts.
+
+@item -m
+@itemx --chars
+@opindex -m
+@opindex --chars
+Print only the character counts.
+
+@item -w
+@itemx --words
+@opindex -w
+@opindex --words
+Print only the word counts.
+
+@item -l
+@itemx --lines
+@opindex -l
+@opindex --lines
+Print only the newline counts.
+
+@item -L
+@itemx --max-line-length
+@opindex -L
+@opindex --max-line-length
+Print only the maximum line lengths.
+
+@macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
+@itemx --files0-from=@var{file}
+@opindex --files0-from=@var{file}
+@c This is commented out to avoid a texi2dvi failure.
+@c texi2dvi (GNU Texinfo 4.11) 1.104
+@c @cindex including files from @command{\cmd\}
+Disallow processing files named on the command line, and instead process
+those named in file @var{file}; each name being terminated by a zero byte
+(@acronym{ASCII} @sc{nul}).
+This is useful \withTotalOption\
+when the list of file names is so long that it may exceed a command line
+length limitation.
+In such cases, running @command{\cmd\} via @command{xargs} is undesirable
+because it splits the list into pieces and makes @command{\cmd\} print
+\subListOutput\ for each sublist rather than for the entire list.
+One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
+@command{find}, using its @option{-print0} predicate.
+If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
+are read from standard input.
+@end macro
+@filesZeroFromOption{wc,,a total}
+
+For example, to find the length of the longest line in any @file{.c} or
+@file{.h} file in the current hierarchy, do this:
+
+@example
+find . -name '*.[ch]' -print0 |
+ wc -L --files0-from=- | tail -n1
+@end example
+
+@end table
+
+@exitstatus
+
+
+@node sum invocation
+@section @command{sum}: Print checksum and block counts
+
+@pindex sum
+@cindex 16-bit checksum
+@cindex checksum, 16-bit
+
+@command{sum} computes a 16-bit checksum for each given @var{file}, or
+standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
+
+@example
+sum [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@command{sum} prints the checksum for each @var{file} followed by the
+number of blocks in the file (rounded up). If more than one @var{file}
+is given, file names are also printed (by default). (With the
+@option{--sysv} option, corresponding file names are printed when there is
+at least one file argument.)
+
+By default, @sc{gnu} @command{sum} computes checksums using an algorithm
+compatible with BSD @command{sum} and prints file sizes in units of
+1024-byte blocks.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -r
+@opindex -r
+@cindex BSD @command{sum}
+Use the default (BSD compatible) algorithm. This option is included for
+compatibility with the System V @command{sum}. Unless @option{-s} was also
+given, it has no effect.
+
+@item -s
+@itemx --sysv
+@opindex -s
+@opindex --sysv
+@cindex System V @command{sum}
+Compute checksums using an algorithm compatible with System V
+@command{sum}'s default, and print file sizes in units of 512-byte blocks.
+
+@end table
+
+@command{sum} is provided for compatibility; the @command{cksum} program (see
+next section) is preferable in new applications.
+
+@exitstatus
+
+
+@node cksum invocation
+@section @command{cksum}: Print CRC checksum and byte counts
+
+@pindex cksum
+@cindex cyclic redundancy check
+@cindex CRC checksum
+
+@command{cksum} computes a cyclic redundancy check (CRC) checksum for each
+given @var{file}, or standard input if none are given or for a
+@var{file} of @samp{-}. Synopsis:
+
+@example
+cksum [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@command{cksum} prints the CRC checksum for each file along with the number
+of bytes in the file, and the file name unless no arguments were given.
+
+@command{cksum} is typically used to ensure that files
+transferred by unreliable means (e.g., netnews) have not been corrupted,
+by comparing the @command{cksum} output for the received files with the
+@command{cksum} output for the original files (typically given in the
+distribution).
+
+The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
+compatible with the BSD or System V @command{sum} algorithms (see the
+previous section); it is more robust.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node md5sum invocation
+@section @command{md5sum}: Print or check MD5 digests
+
+@pindex md5sum
+@cindex MD5
+@cindex 128-bit checksum
+@cindex checksum, 128-bit
+@cindex fingerprint, 128-bit
+@cindex message-digest, 128-bit
+
+@command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
+@dfn{message-digest}) for each specified @var{file}.
+
+Note: The MD5 digest is more reliable than a simple CRC (provided by
+the @command{cksum} command) for detecting accidental file corruption,
+as the chances of accidentally having two files with identical MD5
+are vanishingly small. However, it should not be considered truly
+secure against malicious tampering: although finding a file with a
+given MD5 fingerprint, or modifying a file so as to retain its MD5 are
+considered infeasible at the moment, it is known how to produce
+different files with identical MD5 (a ``collision''), something which
+can be a security issue in certain contexts. For more secure hashes,
+consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
+@ref{sha2 utilities}.
+
+If a @var{file} is specified as @samp{-} or if no files are given
+@command{md5sum} computes the checksum for the standard input.
+@command{md5sum} can also determine whether a file and checksum are
+consistent. Synopsis:
+
+@example
+md5sum [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
+indicating a binary or text input file, and the file name.
+If @var{file} contains a backslash or newline, the
+line is started with a backslash, and each problematic character in
+the file name is escaped with a backslash, making the output
+unambiguous even in the presence of arbitrary file names.
+If @var{file} is omitted or specified as @samp{-}, standard input is read.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -b
+@itemx --binary
+@opindex -b
+@opindex --binary
+@cindex binary input files
+Treat each input file as binary, by reading it in binary mode and
+outputting a @samp{*} flag. This is the inverse of @option{--text}.
+On systems like @acronym{GNU} that do not distinguish between binary
+and text files, this option merely flags each input file as binary:
+the MD5 checksum is unaffected. This option is the default on systems
+like MS-DOS that distinguish between binary and text files, except
+for reading standard input when standard input is a terminal.
+
+@item -c
+@itemx --check
+Read file names and checksum information (not data) from each
+@var{file} (or from stdin if no @var{file} was specified) and report
+whether the checksums match the contents of the named files.
+The input to this mode of @command{md5sum} is usually the output of
+a prior, checksum-generating run of @samp{md5sum}.
+Each valid line of input consists of an MD5 checksum, a binary/text
+flag, and then a file name.
+Binary files are marked with @samp{*}, text with @samp{ }.
+For each such line, @command{md5sum} reads the named file and computes its
+MD5 checksum. Then, if the computed message digest does not match the
+one on the line with the file name, the file is noted as having
+failed the test. Otherwise, the file passes the test.
+By default, for each valid line, one line is written to standard
+output indicating whether the named file passed the test.
+After all checks have been performed, if there were any failures,
+a warning is issued to standard error.
+Use the @option{--status} option to inhibit that output.
+If any listed file cannot be opened or read, if any valid line has
+an MD5 checksum inconsistent with the associated file, or if no valid
+line is found, @command{md5sum} exits with nonzero status. Otherwise,
+it exits successfully.
+
+@itemx --quiet
+@opindex --quiet
+@cindex verifying MD5 checksums
+This option is useful only when verifying checksums.
+When verifying checksums, don't generate an 'OK' message per successfully
+checked file. Files that fail the verification are reported in the
+default one-line-per-file format. If there is any checksum mismatch,
+print a warning summarizing the failures to standard error.
+
+@itemx --status
+@opindex --status
+@cindex verifying MD5 checksums
+This option is useful only when verifying checksums.
+When verifying checksums, don't generate the default one-line-per-file
+diagnostic and don't output the warning summarizing any failures.
+Failures to open or read a file still evoke individual diagnostics to
+standard error.
+If all listed files are readable and are consistent with the associated
+MD5 checksums, exit successfully. Otherwise exit with a status code
+indicating there was a failure.
+
+@item -t
+@itemx --text
+@opindex -t
+@opindex --text
+@cindex text input files
+Treat each input file as text, by reading it in text mode and
+outputting a @samp{ } flag. This is the inverse of @option{--binary}.
+This option is the default on systems like @acronym{GNU} that do not
+distinguish between binary and text files. On other systems, it is
+the default for reading standard input when standard input is a
+terminal.
+
+@item -w
+@itemx --warn
+@opindex -w
+@opindex --warn
+@cindex verifying MD5 checksums
+When verifying checksums, warn about improperly formatted MD5 checksum lines.
+This option is useful only if all but a few lines in the checked input
+are valid.
+
+@end table
+
+@exitstatus
+
+
+@node sha1sum invocation
+@section @command{sha1sum}: Print or check SHA-1 digests
+
+@pindex sha1sum
+@cindex SHA-1
+@cindex 160-bit checksum
+@cindex checksum, 160-bit
+@cindex fingerprint, 160-bit
+@cindex message-digest, 160-bit
+
+@command{sha1sum} computes a 160-bit checksum for each specified
+@var{file}. The usage and options of this command are precisely the
+same as for @command{md5sum}. @xref{md5sum invocation}.
+
+Note: The SHA-1 digest is more secure than MD5, and no collisions of
+it are known (different files having the same fingerprint). However,
+it is known that they can be produced with considerable, but not
+unreasonable, resources. For this reason, it is generally considered
+that SHA-1 should be gradually phased out in favor of the more secure
+SHA-2 hash algorithms. @xref{sha2 utilities}.
+
+
+@node sha2 utilities
+@section sha2 utilities: Print or check SHA-2 digests
+
+@pindex sha224sum
+@pindex sha256sum
+@pindex sha384sum
+@pindex sha512sum
+@cindex SHA-2
+@cindex 224-bit checksum
+@cindex 256-bit checksum
+@cindex 384-bit checksum
+@cindex 512-bit checksum
+@cindex checksum, 224-bit
+@cindex checksum, 256-bit
+@cindex checksum, 384-bit
+@cindex checksum, 512-bit
+@cindex fingerprint, 224-bit
+@cindex fingerprint, 256-bit
+@cindex fingerprint, 384-bit
+@cindex fingerprint, 512-bit
+@cindex message-digest, 224-bit
+@cindex message-digest, 256-bit
+@cindex message-digest, 384-bit
+@cindex message-digest, 512-bit
+
+The commands @command{sha224sum}, @command{sha256sum},
+@command{sha384sum} and @command{sha512sum} compute checksums of
+various lengths (respectively 224, 256, 384 and 512 bits),
+collectively known as the SHA-2 hashes. The usage and options of
+these commands are precisely the same as for @command{md5sum}.
+@xref{md5sum invocation}.
+
+Note: The SHA384 and SHA512 digests are considerably slower to
+compute, especially on 32-bit computers, than SHA224 or SHA256.
+
+
+@node Operating on sorted files
+@chapter Operating on sorted files
+
+@cindex operating on sorted files
+@cindex sorted files, operations on
+
+These commands work with (or produce) sorted files.
+
+@menu
+* sort invocation:: Sort text files.
+* shuf invocation:: Shuffle text files.
+* uniq invocation:: Uniquify files.
+* comm invocation:: Compare two sorted files line by line.
+* ptx invocation:: Produce a permuted index of file contents.
+* tsort invocation:: Topological sort.
+@end menu
+
+
+@node sort invocation
+@section @command{sort}: Sort text files
+
+@pindex sort
+@cindex sorting files
+
+@command{sort} sorts, merges, or compares all the lines from the given
+files, or standard input if none are given or for a @var{file} of
+@samp{-}. By default, @command{sort} writes the results to standard
+output. Synopsis:
+
+@example
+sort [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@command{sort} has three modes of operation: sort (the default), merge,
+and check for sortedness. The following options change the operation
+mode:
+
+@table @samp
+
+@item -c
+@itemx --check
+@itemx --check=diagnose-first
+@opindex -c
+@opindex --check
+@cindex checking for sortedness
+Check whether the given file is already sorted: if it is not all
+sorted, print a diagnostic containing the first out-of-order line and
+exit with a status of 1.
+Otherwise, exit successfully.
+At most one input file can be given.
+
+@item -C
+@itemx --check=quiet
+@itemx --check=silent
+@opindex -c
+@opindex --check
+@cindex checking for sortedness
+Exit successfully if the given file is already sorted, and
+exit with status 1 otherwise.
+At most one input file can be given.
+This is like @option{-c}, except it does not print a diagnostic.
+
+@item -m
+@itemx --merge
+@opindex -m
+@opindex --merge
+@cindex merging sorted files
+Merge the given files by sorting them as a group. Each input file must
+always be individually sorted. It always works to sort instead of
+merge; merging is provided because it is faster, in the case where it
+works.
+
+@end table
+
+@cindex sort stability
+@cindex sort's last-resort comparison
+A pair of lines is compared as follows:
+@command{sort} compares each pair of fields, in the
+order specified on the command line, according to the associated
+ordering options, until a difference is found or no fields are left.
+If no key fields are specified, @command{sort} uses a default key of
+the entire line. Finally, as a last resort when all keys compare
+equal, @command{sort} compares entire lines as if no ordering options
+other than @option{--reverse} (@option{-r}) were specified. The
+@option{--stable} (@option{-s}) option disables this @dfn{last-resort
+comparison} so that lines in which all fields compare equal are left
+in their original relative order. The @option{--unique}
+(@option{-u}) option also disables the last-resort comparison.
+
+@vindex LC_ALL
+@vindex LC_COLLATE
+Unless otherwise specified, all comparisons use the character collating
+sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
+use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
+to @samp{en_US}), then @command{sort} may produce output that is sorted
+differently than you're accustomed to. In that case, set the @env{LC_ALL}
+environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
+has two problems. First, it is ineffective if @env{LC_ALL} is also set.
+Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
+@env{LC_CTYPE} is unset) is set to an incompatible value. For example,
+you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
+@env{LC_COLLATE} is @code{en_US.UTF-8}.}
+
+@sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
+limit on input line length or restrictions on bytes allowed within lines.
+In addition, if the final byte of an input file is not a newline, @sc{gnu}
+@command{sort} silently supplies one. A line's trailing newline is not
+part of the line for comparison purposes.
+
+@cindex exit status of @command{sort}
+Exit status:
+
+@display
+0 if no error occurred
+1 if invoked with @option{-c} or @option{-C} and the input is not sorted
+2 if an error occurred
+@end display
+
+@vindex TMPDIR
+If the environment variable @env{TMPDIR} is set, @command{sort} uses its
+value as the directory for temporary files instead of @file{/tmp}. The
+@option{--temporary-directory} (@option{-T}) option in turn overrides
+the environment variable.
+
+The following options affect the ordering of output lines. They may be
+specified globally or as part of a specific key field. If no key
+fields are specified, global options apply to comparison of entire
+lines; otherwise the global options are inherited by key fields that do
+not specify any special options of their own. In pre-@acronym{POSIX}
+versions of @command{sort}, global options affect only later key fields,
+so portable shell scripts should specify global options first.
+
+@table @samp
+
+@item -b
+@itemx --ignore-leading-blanks
+@opindex -b
+@opindex --ignore-leading-blanks
+@cindex blanks, ignoring leading
+@vindex LC_CTYPE
+Ignore leading blanks when finding sort keys in each line.
+By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
+can change this.
+
+@item -d
+@itemx --dictionary-order
+@opindex -d
+@opindex --dictionary-order
+@cindex dictionary order
+@cindex phone directory order
+@cindex telephone directory order
+@vindex LC_CTYPE
+Sort in @dfn{phone directory} order: ignore all characters except
+letters, digits and blanks when sorting.
+By default letters and digits are those of @acronym{ASCII} and a blank
+is a space or a tab, but the @env{LC_CTYPE} locale can change this.
+
+@item -f
+@itemx --ignore-case
+@opindex -f
+@opindex --ignore-case
+@cindex ignoring case
+@cindex case folding
+@vindex LC_CTYPE
+Fold lowercase characters into the equivalent uppercase characters when
+comparing so that, for example, @samp{b} and @samp{B} sort as equal.
+The @env{LC_CTYPE} locale determines character types.
+When used with @option{--unique} those lower case equivalent lines are
+thrown away. (There is currently no way to throw away the upper case
+equivalent instead. (Any @option{--reverse} given would only affect
+the final result, after the throwing away.))
+
+@item -g
+@itemx --general-numeric-sort
+@itemx --sort=general-numeric
+@opindex -g
+@opindex --general-numeric-sort
+@opindex --sort
+@cindex general numeric sort
+@vindex LC_NUMERIC
+Sort numerically, using the standard C function @code{strtod} to convert
+a prefix of each line to a double-precision floating point number.
+This allows floating point numbers to be specified in scientific notation,
+like @code{1.0e-34} and @code{10e100}.
+The @env{LC_NUMERIC} locale determines the decimal-point character.
+Do not report overflow, underflow, or conversion errors.
+Use the following collating sequence:
+
+@itemize @bullet
+@item
+Lines that do not start with numbers (all considered to be equal).
+@item
+NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
+in a consistent but machine-dependent order.
+@item
+Minus infinity.
+@item
+Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
+@item
+Plus infinity.
+@end itemize
+
+Use this option only if there is no alternative; it is much slower than
+@option{--numeric-sort} (@option{-n}) and it can lose information when
+converting to floating point.
+
+@item -i
+@itemx --ignore-nonprinting
+@opindex -i
+@opindex --ignore-nonprinting
+@cindex nonprinting characters, ignoring
+@cindex unprintable characters, ignoring
+@vindex LC_CTYPE
+Ignore nonprinting characters.
+The @env{LC_CTYPE} locale determines character types.
+This option has no effect if the stronger @option{--dictionary-order}
+(@option{-d}) option is also given.
+
+@item -M
+@itemx --month-sort
+@itemx --sort=month
+@opindex -M
+@opindex --month-sort
+@opindex --sort
+@cindex months, sorting by
+@vindex LC_TIME
+An initial string, consisting of any amount of blanks, followed
+by a month name abbreviation, is folded to UPPER case and
+compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
+Invalid names compare low to valid names. The @env{LC_TIME} locale
+category determines the month spellings.
+By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
+can change this.
+
+@item -n
+@itemx --numeric-sort
+@itemx --sort=numeric
+@opindex -n
+@opindex --numeric-sort
+@opindex --sort
+@cindex numeric sort
+@vindex LC_NUMERIC
+Sort numerically. The number begins each line and consists
+of optional blanks, an optional @samp{-} sign, and zero or more
+digits possibly separated by thousands separators, optionally followed
+by a decimal-point character and zero or more digits. An empty
+number is treated as @samp{0}. The @env{LC_NUMERIC}
+locale specifies the decimal-point character and thousands separator.
+By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
+can change this.
+
+Comparison is exact; there is no rounding error.
+
+Neither a leading @samp{+} nor exponential notation is recognized.
+To compare such strings numerically, use the
+@option{--general-numeric-sort} (@option{-g}) option.
+
+@item -V
+@itemx --version-sort
+@opindex -V
+@opindex --version-sort
+@cindex version number sort
+@vindex LC_NUMERIC
+Sort per @code{strverscmp(3)}. This is a normal string comparison, except
+that embedded decimal numbers are sorted by numeric value
+(see @option{--numeric-sort} above).
+
+@item -r
+@itemx --reverse
+@opindex -r
+@opindex --reverse
+@cindex reverse sorting
+Reverse the result of comparison, so that lines with greater key values
+appear earlier in the output instead of later.
+
+@item -R
+@itemx --random-sort
+@itemx --sort=random
+@opindex -R
+@opindex --random-sort
+@opindex --sort
+@cindex random sort
+Sort by hashing the input keys and then sorting the hash values.
+Choose the hash function at random, ensuring that it is free of
+collisions so that differing keys have differing hash values. This is
+like a random permutation of the inputs (@pxref{shuf invocation}),
+except that keys with the same value sort together.
+
+If multiple random sort fields are specified, the same random hash
+function is used for all fields. To use different random hash
+functions for different fields, you can invoke @command{sort} more
+than once.
+
+The choice of hash function is affected by the
+@option{--random-source} option.
+
+@end table
+
+Other options are:
+
+@table @samp
+
+@item --compress-program=@var{prog}
+Compress any temporary files with the program @var{prog}.
+
+With no arguments, @var{prog} must compress standard input to standard
+output, and when given the @option{-d} option it must decompress
+standard input to standard output.
+
+Terminate with an error if @var{prog} exits with nonzero status.
+
+White space and the backslash character should not appear in
+@var{prog}; they are reserved for future use.
+
+@filesZeroFromOption{sort,,sorted output}
+
+@item -k @var{pos1}[,@var{pos2}]
+@itemx --key=@var{pos1}[,@var{pos2}]
+@opindex -k
+@opindex --key
+@cindex sort field
+Specify a sort field that consists of the part of the line between
+@var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
+omitted), @emph{inclusive}.
+
+Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
+where @var{f} is the number of the field to use, and @var{c} is the number
+of the first character from the beginning of the field. Fields and character
+positions are numbered starting with 1; a character position of zero in
+@var{pos2} indicates the field's last character. If @samp{.@var{c}} is
+omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
+if omitted from @var{pos2}, it defaults to 0 (the end of the field).
+@var{opts} are ordering options, allowing individual keys to be sorted
+according to different rules; see below for details. Keys can span
+multiple fields.
+
+Example: To sort on the second field, use @option{--key=2,2}
+(@option{-k 2,2}). See below for more examples.
+
+@item --batch-size=@var{nmerge}
+@opindex --batch-size
+@cindex number of inputs to merge, nmerge
+Merge at most @var{nmerge} inputs at once.
+
+When @command{sort} has to merge more than @var{nmerge} inputs,
+it merges them in groups of @var{nmerge}, saving the result in
+a temporary file, which is then used as an input in a subsequent merge.
+
+A large value of @var{nmerge} may improve merge performance and decrease
+temporary storage utilization at the expense of increased memory usage
+and I/0. Conversely a small value of @var{nmerge} may reduce memory
+requirements and I/0 at the expense of temporary storage consumption and
+merge performance.
+
+The value of @var{nmerge} must be at least 2. The default value is
+currently 16, but this is implementation-dependent and may change in
+the future.
+
+The value of @var{nmerge} may be bounded by a resource limit for open
+file descriptors. The commands @samp{ulimit -n} or @samp{getconf
+OPEN_MAX} may display limits for your systems; these limits may be
+modified further if your program already has some files open, or if
+the operating system has other limits on the number of open files. If
+the value of @var{nmerge} exceeds the resource limit, @command{sort}
+silently uses a smaller value.
+
+@item -o @var{output-file}
+@itemx --output=@var{output-file}
+@opindex -o
+@opindex --output
+@cindex overwriting of input, allowed
+Write output to @var{output-file} instead of standard output.
+Normally, @command{sort} reads all input before opening
+@var{output-file}, so you can safely sort a file in place by using
+commands like @code{sort -o F F} and @code{cat F | sort -o F}.
+However, @command{sort} with @option{--merge} (@option{-m}) can open
+the output file before reading all input, so a command like @code{cat
+F | sort -m -o F - G} is not safe as @command{sort} might start
+writing @file{F} before @command{cat} is done reading it.
+
+@vindex POSIXLY_CORRECT
+On newer systems, @option{-o} cannot appear after an input file if
+@env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
+scripts should specify @option{-o @var{output-file}} before any input
+files.
+
+@item --random-source=@var{file}
+@opindex --random-source
+@cindex random source for sorting
+Use @var{file} as a source of random data used to determine which
+random hash function to use with the @option{-R} option. @xref{Random
+sources}.
+
+@item -s
+@itemx --stable
+@opindex -s
+@opindex --stable
+@cindex sort stability
+@cindex sort's last-resort comparison
+
+Make @command{sort} stable by disabling its last-resort comparison.
+This option has no effect if no fields or global ordering options
+other than @option{--reverse} (@option{-r}) are specified.
+
+@item -S @var{size}
+@itemx --buffer-size=@var{size}
+@opindex -S
+@opindex --buffer-size
+@cindex size for main memory sorting
+Use a main-memory sort buffer of the given @var{size}. By default,
+@var{size} is in units of 1024 bytes. Appending @samp{%} causes
+@var{size} to be interpreted as a percentage of physical memory.
+Appending @samp{K} multiplies @var{size} by 1024 (the default),
+@samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
+@samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
+@samp{b} causes @var{size} to be interpreted as a byte count, with no
+multiplication.
+
+This option can improve the performance of @command{sort} by causing it
+to start with a larger or smaller sort buffer than the default.
+However, this option affects only the initial buffer size. The buffer
+grows beyond @var{size} if @command{sort} encounters input lines larger
+than @var{size}.
+
+@item -t @var{separator}
+@itemx --field-separator=@var{separator}
+@opindex -t
+@opindex --field-separator
+@cindex field separator character
+Use character @var{separator} as the field separator when finding the
+sort keys in each line. By default, fields are separated by the empty
+string between a non-blank character and a blank character.
+By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
+can change this.
+
+That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
+into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
+not considered to be part of either the field preceding or the field
+following, so with @samp{sort @w{-t " "}} the same input line has
+three fields: an empty field, @samp{foo}, and @samp{bar}.
+However, fields that extend to the end of the line,
+as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
+retain the field separators present between the endpoints of the range.
+
+To specify @acronym{ASCII} @sc{nul} as the field separator,
+use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
+
+@item -T @var{tempdir}
+@itemx --temporary-directory=@var{tempdir}
+@opindex -T
+@opindex --temporary-directory
+@cindex temporary directory
+@vindex TMPDIR
+Use directory @var{tempdir} to store temporary files, overriding the
+@env{TMPDIR} environment variable. If this option is given more than
+once, temporary files are stored in all the directories given. If you
+have a large sort or merge that is I/O-bound, you can often improve
+performance by using this option to specify directories on different
+disks and controllers.
+
+@item -u
+@itemx --unique
+@opindex -u
+@opindex --unique
+@cindex uniquifying output
+
+Normally, output only the first of a sequence of lines that compare
+equal. For the @option{--check} (@option{-c} or @option{-C}) option,
+check that no pair of consecutive lines compares equal.
+
+This option also disables the default last-resort comparison.
+
+The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
+this equivalence does not extend to arbitrary @command{sort} options.
+For example, @code{sort -n -u} inspects only the value of the initial
+numeric string when checking for uniqueness, whereas @code{sort -n |
+uniq} inspects the entire line. @xref{uniq invocation}.
+
+@macro zeroTerminatedOption
+@item -z
+@itemx --zero-terminated
+@opindex -z
+@opindex --zero-terminated
+@cindex process zero-terminated items
+Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
+I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
+and terminate output items with @acronym{ASCII} @sc{nul}.
+This option can be useful in conjunction with @samp{perl -0} or
+@samp{find -print0} and @samp{xargs -0} which do the same in order to
+reliably handle arbitrary file names (even those containing blanks
+or other special characters).
+@end macro
+@zeroTerminatedOption
+
+@end table
+
+Historical (BSD and System V) implementations of @command{sort} have
+differed in their interpretation of some options, particularly
+@option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
+behavior, which is usually (but not always!) like the System V behavior.
+According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
+consistency, @option{-M} has been changed in the same way. This may
+affect the meaning of character positions in field specifications in
+obscure cases. The only fix is to add an explicit @option{-b}.
+
+A position in a sort field specified with @option{-k} may have any
+of the option letters @samp{Mbdfinr} appended to it, in which case the
+global ordering options are not used for that particular field. The
+@option{-b} option may be independently attached to either or both of
+the start and end positions of a field specification, and if it is
+inherited from the global options it will be attached to both.
+If input lines can contain leading or adjacent blanks and @option{-t}
+is not used, then @option{-k} is typically combined with @option{-b},
+@option{-g}, @option{-M}, or @option{-n}; otherwise the varying
+numbers of leading blanks in fields can cause confusing results.
+
+If the start position in a sort field specifier falls after the end of
+the line or after the end field, the field is empty. If the @option{-b}
+option was specified, the @samp{.@var{c}} part of a field specification
+is counted from the first nonblank character of the field.
+
+@vindex _POSIX2_VERSION
+@vindex POSIXLY_CORRECT
+On older systems, @command{sort} supports an obsolete origin-zero
+syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
+This obsolete behavior can be enabled or disabled with the
+@env{_POSIX2_VERSION} environment variable (@pxref{Standards
+conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
+not set by using the obsolete syntax with @samp{-@var{pos2}} present.
+
+Scripts intended for use on standard hosts should avoid obsolete
+syntax and should use @option{-k} instead. For example, avoid
+@samp{sort +2}, since it might be interpreted as either @samp{sort
+./+2} or @samp{sort -k 3}. If your script must also run on hosts that
+support only the obsolete syntax, it can use a test like @samp{if sort
+-k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
+to use.
+
+Here are some examples to illustrate various combinations of options.
+
+@itemize @bullet
+
+@item
+Sort in descending (reverse) numeric order.
+
+@example
+sort -n -r
+@end example
+
+@item
+Sort alphabetically, omitting the first and second fields
+and the blanks at the start of the third field.
+This uses a single key composed of the characters beginning
+at the start of the first nonblank character in field three
+and extending to the end of each line.
+
+@example
+sort -k 3b
+@end example
+
+@item
+Sort numerically on the second field and resolve ties by sorting
+alphabetically on the third and fourth characters of field five.
+Use @samp{:} as the field delimiter.
+
+@example
+sort -t : -k 2,2n -k 5.3,5.4
+@end example
+
+Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
+@command{sort} would have used all characters beginning in the second field
+and extending to the end of the line as the primary @emph{numeric}
+key. For the large majority of applications, treating keys spanning
+more than one field as numeric will not do what you expect.
+
+Also note that the @samp{n} modifier was applied to the field-end
+specifier for the first key. It would have been equivalent to
+specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
+@samp{b} apply to the associated @emph{field}, regardless of whether
+the modifier character is attached to the field-start and/or the
+field-end part of the key specifier.
+
+@item
+Sort the password file on the fifth field and ignore any
+leading blanks. Sort lines with equal values in field five
+on the numeric user ID in field three. Fields are separated
+by @samp{:}.
+
+@example
+sort -t : -k 5b,5 -k 3,3n /etc/passwd
+sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
+sort -t : -b -k 5,5 -k 3,3n /etc/passwd
+@end example
+
+These three commands have equivalent effect. The first specifies that
+the first key's start position ignores leading blanks and the second
+key is sorted numerically. The other two commands rely on global
+options being inherited by sort keys that lack modifiers. The inheritance
+works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
+equivalent, as the location of a field-end lacking a @samp{.@var{c}}
+character position is not affected by whether initial blanks are
+skipped.
+
+@item
+Sort a set of log files, primarily by IPv4 address and secondarily by
+time stamp. If two lines' primary and secondary keys are identical,
+output the lines in the same order that they were input. The log
+files contain lines that look like this:
+
+@example
+4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
+211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
+@end example
+
+Fields are separated by exactly one space. Sort IPv4 addresses
+lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
+because 61 is less than 129.
+
+@example
+sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
+sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
+@end example
+
+This example cannot be done with a single @command{sort} invocation,
+since IPv4 address components are separated by @samp{.} while dates
+come just after a space. So it is broken down into two invocations of
+@command{sort}: the first sorts by time stamp and the second by IPv4
+address. The time stamp is sorted by year, then month, then day, and
+finally by hour-minute-second field, using @option{-k} to isolate each
+field. Except for hour-minute-second there's no need to specify the
+end of each key field, since the @samp{n} and @samp{M} modifiers sort
+based on leading prefixes that cannot cross field boundaries. The
+IPv4 addresses are sorted lexicographically. The second sort uses
+@samp{-s} so that ties in the primary key are broken by the secondary
+key; the first sort uses @samp{-s} so that the combination of the two
+sorts is stable.
+
+@item
+Generate a tags file in case-insensitive sorted order.
+
+@smallexample
+find src -type f -print0 | sort -z -f | xargs -0 etags --append
+@end smallexample
+
+The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
+that file names that contain blanks or other special characters are
+not broken up
+by the sort operation.
+
+@c This example is a bit contrived and needs more explanation.
+@c @item
+@c Sort records separated by an arbitrary string by using a pipe to convert
+@c each record delimiter string to @samp{\0}, then using sort's -z option,
+@c and converting each @samp{\0} back to the original record delimiter.
+@c
+@c @example
+@c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
+@c @end example
+
+@item
+Shuffle a list of directories, but preserve the order of files within
+each directory. For instance, one could use this to generate a music
+playlist in which albums are shuffled but the songs of each album are
+played in order.
+
+@example
+ls */* | sort -t / -k 1,1R -k 2,2
+@end example
+
+@end itemize
+
+
+@node shuf invocation
+@section @command{shuf}: Shuffling text
+
+@pindex shuf
+@cindex shuffling files
+
+@command{shuf} shuffles its input by outputting a random permutation
+of its input lines. Each output permutation is equally likely.
+Synopses:
+
+@example
+shuf [@var{option}]@dots{} [@var{file}]
+shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
+shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
+@end example
+
+@command{shuf} has three modes of operation that affect where it
+obtains its input lines. By default, it reads lines from standard
+input. The following options change the operation mode:
+
+@table @samp
+
+@item -e
+@itemx --echo
+@opindex -c
+@opindex --echo
+@cindex command-line operands to shuffle
+Treat each command-line operand as an input line.
+
+@item -i @var{lo}-@var{hi}
+@itemx --input-range=@var{lo}-@var{hi}
+@opindex -i
+@opindex --input-range
+@cindex input range to shuffle
+Act as if input came from a file containing the range of unsigned
+decimal integers @var{lo}@dots{}@var{hi}, one per line.
+
+@end table
+
+@command{shuf}'s other options can affect its behavior in all
+operation modes:
+
+@table @samp
+
+@item -n @var{lines}
+@itemx --head-count=@var{count}
+@opindex -n
+@opindex --head-count
+@cindex head of output
+Output at most @var{count} lines. By default, all input lines are
+output.
+
+@item -o @var{output-file}
+@itemx --output=@var{output-file}
+@opindex -o
+@opindex --output
+@cindex overwriting of input, allowed
+Write output to @var{output-file} instead of standard output.
+@command{shuf} reads all input before opening
+@var{output-file}, so you can safely shuffle a file in place by using
+commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
+
+@item --random-source=@var{file}
+@opindex --random-source
+@cindex random source for shuffling
+Use @var{file} as a source of random data used to determine which
+permutation to generate. @xref{Random sources}.
+
+@zeroTerminatedOption
+
+@end table
+
+For example:
+
+@example
+shuf <<EOF
+A man,
+a plan,
+a canal:
+Panama!
+EOF
+@end example
+
+@noindent
+might produce the output
+
+@example
+Panama!
+A man,
+a canal:
+a plan,
+@end example
+
+@noindent
+Similarly, the command:
+
+@example
+shuf -e clubs hearts diamonds spades
+@end example
+
+@noindent
+might output:
+
+@example
+clubs
+diamonds
+spades
+hearts
+@end example
+
+@noindent
+and the command @samp{shuf -i 1-4} might output:
+
+@example
+4
+2
+1
+3
+@end example
+
+@noindent
+These examples all have four input lines, so @command{shuf} might
+produce any of the twenty-four possible permutations of the input. In
+general, if there are @var{n} input lines, there are @var{n}! (i.e.,
+@var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
+output permutations.
+
+@exitstatus
+
+
+@node uniq invocation
+@section @command{uniq}: Uniquify files
+
+@pindex uniq
+@cindex uniquify files
+
+@command{uniq} writes the unique lines in the given @file{input}, or
+standard input if nothing is given or for an @var{input} name of
+@samp{-}. Synopsis:
+
+@example
+uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
+@end example
+
+By default, @command{uniq} prints its input lines, except that
+it discards all but the first of adjacent repeated lines, so that
+no output lines are repeated. Optionally, it can instead discard
+lines that are not repeated, or all repeated lines.
+
+The input need not be sorted, but repeated input lines are detected
+only if they are adjacent. If you want to discard non-adjacent
+duplicate lines, perhaps you want to use @code{sort -u}.
+@xref{sort invocation}.
+
+@vindex LC_COLLATE
+Comparisons use the character collating sequence specified by the
+@env{LC_COLLATE} locale category.
+
+If no @var{output} file is specified, @command{uniq} writes to standard
+output.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f @var{n}
+@itemx --skip-fields=@var{n}
+@opindex -f
+@opindex --skip-fields
+Skip @var{n} fields on each line before checking for uniqueness. Use
+a null string for comparison if a line has fewer than @var{n} fields. Fields
+are sequences of non-space non-tab characters that are separated from
+each other by at least one space or tab.
+
+For compatibility @command{uniq} supports an obsolete option syntax
+@option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
+
+@item -s @var{n}
+@itemx --skip-chars=@var{n}
+@opindex -s
+@opindex --skip-chars
+Skip @var{n} characters before checking for uniqueness. Use a null string
+for comparison if a line has fewer than @var{n} characters. If you use both
+the field and character skipping options, fields are skipped over first.
+
+@vindex _POSIX2_VERSION
+On older systems, @command{uniq} supports an obsolete option syntax
+@option{+@var{n}}.
+This obsolete behavior can be enabled or disabled with the
+@env{_POSIX2_VERSION} environment variable (@pxref{Standards
+conformance}), but portable scripts should avoid commands whose
+behavior depends on this variable.
+For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
+the ambiguous @samp{uniq +10}.
+
+@item -c
+@itemx --count
+@opindex -c
+@opindex --count
+Print the number of times each line occurred along with the line.
+
+@item -i
+@itemx --ignore-case
+@opindex -i
+@opindex --ignore-case
+Ignore differences in case when comparing lines.
+
+@item -d
+@itemx --repeated
+@opindex -d
+@opindex --repeated
+@cindex repeated lines, outputting
+Discard lines that are not repeated. When used by itself, this option
+causes @command{uniq} to print the first copy of each repeated line,
+and nothing else.
+
+@item -D
+@itemx --all-repeated[=@var{delimit-method}]
+@opindex -D
+@opindex --all-repeated
+@cindex all repeated lines, outputting
+Do not discard the second and subsequent repeated input lines,
+but discard lines that are not repeated.
+This option is useful mainly in conjunction with other options e.g.,
+to ignore case or to compare only selected fields.
+The optional @var{delimit-method} tells how to delimit
+groups of repeated lines, and must be one of the following:
+
+@table @samp
+
+@item none
+Do not delimit groups of repeated lines.
+This is equivalent to @option{--all-repeated} (@option{-D}).
+
+@item prepend
+Output a newline before each group of repeated lines.
+With @option{--zero-terminated} (@option{-z}), use a zero
+byte (@acronym{ASCII} @sc{nul}) instead of a newline.
+
+@item separate
+Separate groups of repeated lines with a single newline.
+With @option{--zero-terminated} (@option{-z}), use a zero
+byte (@acronym{ASCII} @sc{nul}) instead of a newline.
+This is the same as using @samp{prepend}, except that
+no delimiter is inserted before the first group, and hence
+may be better suited for output direct to users.
+@end table
+
+Note that when groups are delimited and the input stream contains
+two or more consecutive blank lines, then the output is ambiguous.
+To avoid that, filter the input through @samp{tr -s '\n'} to replace
+each sequence of consecutive newlines with a single newline.
+
+This is a @sc{gnu} extension.
+@c FIXME: give an example showing *how* it's useful
+
+@item -u
+@itemx --unique
+@opindex -u
+@opindex --unique
+@cindex unique lines, outputting
+Discard the first repeated line. When used by itself, this option
+causes @command{uniq} to print unique lines, and nothing else.
+
+@item -w @var{n}
+@itemx --check-chars=@var{n}
+@opindex -w
+@opindex --check-chars
+Compare at most @var{n} characters on each line (after skipping any specified
+fields and characters). By default the entire rest of the lines are
+compared.
+
+@zeroTerminatedOption
+
+@end table
+
+@exitstatus
+
+
+@node comm invocation
+@section @command{comm}: Compare two sorted files line by line
+
+@pindex comm
+@cindex line-by-line comparison
+@cindex comparing sorted files
+
+@command{comm} writes to standard output lines that are common, and lines
+that are unique, to two input files; a file name of @samp{-} means
+standard input. Synopsis:
+
+@example
+comm [@var{option}]@dots{} @var{file1} @var{file2}
+@end example
+
+@vindex LC_COLLATE
+Before @command{comm} can be used, the input files must be sorted using the
+collating sequence specified by the @env{LC_COLLATE} locale.
+If an input file ends in a non-newline
+character, a newline is silently appended. The @command{sort} command with
+no options always outputs a file that is suitable input to @command{comm}.
+
+@cindex differing lines
+@cindex common lines
+With no options, @command{comm} produces three-column output. Column one
+contains lines unique to @var{file1}, column two contains lines unique
+to @var{file2}, and column three contains lines common to both files.
+Columns are separated by a single TAB character.
+@c FIXME: when there's an option to supply an alternative separator
+@c string, append `by default' to the above sentence.
+
+@opindex -1
+@opindex -2
+@opindex -3
+The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
+the corresponding columns. Also see @ref{Common options}.
+
+Unlike some other comparison utilities, @command{comm} has an exit
+status that does not depend on the result of the comparison.
+Upon normal completion @command{comm} produces an exit code of zero.
+If there is an error it exits with nonzero status.
+
+@macro checkOrderOption{cmd}
+If the @option{--check-order} option is given, unsorted inputs will
+cause a fatal error message. If the option @option{--nocheck-order}
+is given, unsorted inputs will never cause an error message. If
+neither of these options is given, wrongly sorted inputs are diagnosed
+only if an input file is found to contain unpairable lines. If an
+input file is diagnosed as being unsorted, the @command{\cmd\} command
+will exit with a nonzero status (and the output should not be used).
+
+Forcing @command{\cmd\} to process wrongly sorted input files
+containing unpairable lines by specifying @option{--nocheck-order} is
+not guaranteed to produce any particular output. The output will
+probably not correspond with whatever you hoped it would be.
+@end macro
+@checkOrderOption{comm}
+
+@table @samp
+
+@item --check-order
+Fail with an error message if either input file is wrongly ordered.
+
+@item --nocheck-order
+Do not check that both input files are in sorted order.
+
+Other options are:
+
+@item --output-delimiter=@var{str}
+Print @var{str} between adjacent output columns,
+rather than the default of a single TAB character.
+
+The delimiter @var{str} may not be empty.
+
+@end table
+
+@node ptx invocation
+@section @command{ptx}: Produce permuted indexes
+
+@pindex ptx
+
+@command{ptx} reads a text file and essentially produces a permuted index, with
+each keyword in its context. The calling sketch is either one of:
+
+@example
+ptx [@var{option} @dots{}] [@var{file} @dots{}]
+ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
+@end example
+
+The @option{-G} (or its equivalent: @option{--traditional}) option disables
+all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
+limitations and changing several of the program's default option values.
+When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
+@sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
+document. For the full list, see @xref{Compatibility in ptx}.
+
+Individual options are explained in the following sections.
+
+When @sc{gnu} extensions are enabled, there may be zero, one or several
+@var{file}s after the options. If there is no @var{file}, the program
+reads the standard input. If there is one or several @var{file}s, they
+give the name of input files which are all read in turn, as if all the
+input files were concatenated. However, there is a full contextual
+break between each file and, when automatic referencing is requested,
+file names and line numbers refer to individual text input files. In
+all cases, the program outputs the permuted index to the standard
+output.
+
+When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
+operates in traditional mode, there may be zero, one or two parameters
+besides the options. If there are no parameters, the program reads the
+standard input and outputs the permuted index to the standard output.
+If there is only one parameter, it names the text @var{input} to be read
+instead of the standard input. If two parameters are given, they give
+respectively the name of the @var{input} file to read and the name of
+the @var{output} file to produce. @emph{Be very careful} to note that,
+in this case, the contents of file given by the second parameter is
+destroyed. This behavior is dictated by System V @command{ptx}
+compatibility; @sc{gnu} Standards normally discourage output parameters not
+introduced by an option.
+
+Note that for @emph{any} file named as the value of an option or as an
+input text file, a single dash @kbd{-} may be used, in which case
+standard input is assumed. However, it would not make sense to use this
+convention more than once per program invocation.
+
+@menu
+* General options in ptx:: Options which affect general program behavior.
+* Charset selection in ptx:: Underlying character set considerations.
+* Input processing in ptx:: Input fields, contexts, and keyword selection.
+* Output formatting in ptx:: Types of output format, and sizing the fields.
+* Compatibility in ptx::
+@end menu
+
+
+@node General options in ptx
+@subsection General options
+
+@table @samp
+
+@item -G
+@itemx --traditional
+As already explained, this option disables all @sc{gnu} extensions to
+@command{ptx} and switches to traditional mode.
+
+@item --help
+Print a short help on standard output, then exit without further
+processing.
+
+@item --version
+Print the program version on standard output, then exit without further
+processing.
+
+@end table
+
+@exitstatus
+
+
+@node Charset selection in ptx
+@subsection Charset selection
+
+@c FIXME: People don't necessarily know what an IBM-PC was these days.
+As it is set up now, the program assumes that the input file is coded
+using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
+@emph{unless} it is compiled for MS-DOS, in which case it uses the
+character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
+smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
+of characters which are letters is different; this alters the behavior
+of regular expression matching. Thus, the default regular expression
+for a keyword allows foreign or diacriticized letters. Keyword sorting,
+however, is still crude; it obeys the underlying character set ordering
+quite blindly.
+
+@table @samp
+
+@item -f
+@itemx --ignore-case
+Fold lower case letters to upper case for sorting.
+
+@end table
+
+
+@node Input processing in ptx
+@subsection Word selection and input processing
+
+@table @samp
+
+@item -b @var{file}
+@itemx --break-file=@var{file}
+
+This option provides an alternative (to @option{-W}) method of describing
+which characters make up words. It introduces the name of a
+file which contains a list of characters which can@emph{not} be part of
+one word; this file is called the @dfn{Break file}. Any character which
+is not part of the Break file is a word constituent. If both options
+@option{-b} and @option{-W} are specified, then @option{-W} has precedence and
+@option{-b} is ignored.
+
+When @sc{gnu} extensions are enabled, the only way to avoid newline as a
+break character is to write all the break characters in the file with no
+newline at all, not even at the end of the file. When @sc{gnu} extensions
+are disabled, spaces, tabs and newlines are always considered as break
+characters even if not included in the Break file.
+
+@item -i @var{file}
+@itemx --ignore-file=@var{file}
+
+The file associated with this option contains a list of words which will
+never be taken as keywords in concordance output. It is called the
+@dfn{Ignore file}. The file contains exactly one word in each line; the
+end of line separation of words is not subject to the value of the
+@option{-S} option.
+
+@item -o @var{file}
+@itemx --only-file=@var{file}
+
+The file associated with this option contains a list of words which will
+be retained in concordance output; any word not mentioned in this file
+is ignored. The file is called the @dfn{Only file}. The file contains
+exactly one word in each line; the end of line separation of words is
+not subject to the value of the @option{-S} option.
+
+There is no default for the Only file. When both an Only file and an
+Ignore file are specified, a word is considered a keyword only
+if it is listed in the Only file and not in the Ignore file.
+
+@item -r
+@itemx --references
+
+On each input line, the leading sequence of non-white space characters will be
+taken to be a reference that has the purpose of identifying this input
+line in the resulting permuted index. For more information about reference
+production, see @xref{Output formatting in ptx}.
+Using this option changes the default value for option @option{-S}.
+
+Using this option, the program does not try very hard to remove
+references from contexts in output, but it succeeds in doing so
+@emph{when} the context ends exactly at the newline. If option
+@option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
+are disabled, this condition is always met and references are completely
+excluded from the output contexts.
+
+@item -S @var{regexp}
+@itemx --sentence-regexp=@var{regexp}
+
+This option selects which regular expression will describe the end of a
+line or the end of a sentence. In fact, this regular expression is not
+the only distinction between end of lines or end of sentences, and input
+line boundaries have no special significance outside this option. By
+default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
+used, end of sentences are used. In this case, this @var{regex} is
+imported from @sc{gnu} Emacs:
+
+@example
+[.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
+@end example
+
+Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
+of lines are used; in this case, the default @var{regexp} is just:
+
+@example
+\n
+@end example
+
+Using an empty @var{regexp} is equivalent to completely disabling end of
+line or end of sentence recognition. In this case, the whole file is
+considered to be a single big line or sentence. The user might want to
+disallow all truncation flag generation as well, through option @option{-F
+""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
+Manual}.
+
+When the keywords happen to be near the beginning of the input line or
+sentence, this often creates an unused area at the beginning of the
+output context line; when the keywords happen to be near the end of the
+input line or sentence, this often creates an unused area at the end of
+the output context line. The program tries to fill those unused areas
+by wrapping around context in them; the tail of the input line or
+sentence is used to fill the unused area on the left of the output line;
+the head of the input line or sentence is used to fill the unused area
+on the right of the output line.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences from the C language are recognized and converted to the
+corresponding characters by @command{ptx} itself.
+
+@item -W @var{regexp}
+@itemx --word-regexp=@var{regexp}
+
+This option selects which regular expression will describe each keyword.
+By default, if @sc{gnu} extensions are enabled, a word is a sequence of
+letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
+disabled, a word is by default anything which ends with a space, a tab
+or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
+
+An empty @var{regexp} is equivalent to not using this option.
+@xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
+Manual}.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @command{ptx} itself.
+
+@end table
+
+
+@node Output formatting in ptx
+@subsection Output formatting
+
+Output format is mainly controlled by the @option{-O} and @option{-T} options
+described in the table below. When neither @option{-O} nor @option{-T} are
+selected, and if @sc{gnu} extensions are enabled, the program chooses an
+output format suitable for a dumb terminal. Each keyword occurrence is
+output to the center of one line, surrounded by its left and right
+contexts. Each field is properly justified, so the concordance output
+can be readily observed. As a special feature, if automatic
+references are selected by option @option{-A} and are output before the
+left context, that is, if option @option{-R} is @emph{not} selected, then
+a colon is added after the reference; this nicely interfaces with @sc{gnu}
+Emacs @code{next-error} processing. In this default output format, each
+white space character, like newline and tab, is merely changed to
+exactly one space, with no special attempt to compress consecutive
+spaces. This might change in the future. Except for those white space
+characters, every other character of the underlying set of 256
+characters is transmitted verbatim.
+
+Output format is further controlled by the following options.
+
+@table @samp
+
+@item -g @var{number}
+@itemx --gap-size=@var{number}
+
+Select the size of the minimum white space gap between the fields on the
+output line.
+
+@item -w @var{number}
+@itemx --width=@var{number}
+
+Select the maximum output width of each final line. If references are
+used, they are included or excluded from the maximum output width
+depending on the value of option @option{-R}. If this option is not
+selected, that is, when references are output before the left context,
+the maximum output width takes into account the maximum length of all
+references. If this option is selected, that is, when references are
+output after the right context, the maximum output width does not take
+into account the space taken by references, nor the gap that precedes
+them.
+
+@item -A
+@itemx --auto-reference
+
+Select automatic references. Each input line will have an automatic
+reference made up of the file name and the line ordinal, with a single
+colon between them. However, the file name will be empty when standard
+input is being read. If both @option{-A} and @option{-r} are selected, then
+the input reference is still read and skipped, but the automatic
+reference is used at output time, overriding the input reference.
+
+@item -R
+@itemx --right-side-refs
+
+In the default output format, when option @option{-R} is not used, any
+references produced by the effect of options @option{-r} or @option{-A} are
+placed to the far right of output lines, after the right context. With
+default output format, when the @option{-R} option is specified, references
+are rather placed at the beginning of each output line, before the left
+context. For any other output format, option @option{-R} is
+ignored, with one exception: with @option{-R} the width of references
+is @emph{not} taken into account in total output width given by @option{-w}.
+
+This option is automatically selected whenever @sc{gnu} extensions are
+disabled.
+
+@item -F @var{string}
+@itemx --flac-truncation=@var{string}
+
+This option will request that any truncation in the output be reported
+using the string @var{string}. Most output fields theoretically extend
+towards the beginning or the end of the current line, or current
+sentence, as selected with option @option{-S}. But there is a maximum
+allowed output line width, changeable through option @option{-w}, which is
+further divided into space for various output fields. When a field has
+to be truncated because it cannot extend beyond the beginning or the end of
+the current line to fit in, then a truncation occurs. By default,
+the string used is a single slash, as in @option{-F /}.
+
+@var{string} may have more than one character, as in @option{-F ...}.
+Also, in the particular case when @var{string} is empty (@option{-F ""}),
+truncation flagging is disabled, and no truncation marks are appended in
+this case.
+
+As a matter of convenience to the user, many usual backslashed escape
+sequences, as found in the C language, are recognized and converted to
+the corresponding characters by @command{ptx} itself.
+
+@item -M @var{string}
+@itemx --macro-name=@var{string}
+
+Select another @var{string} to be used instead of @samp{xx}, while
+generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
+
+@item -O
+@itemx --format=roff
+
+Choose an output format suitable for @command{nroff} or @command{troff}
+processing. Each output line will look like:
+
+@smallexample
+.xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
+@end smallexample
+
+so it will be possible to write a @samp{.xx} roff macro to take care of
+the output typesetting. This is the default output format when @sc{gnu}
+extensions are disabled. Option @option{-M} can be used to change
+@samp{xx} to another macro name.
+
+In this output format, each non-graphical character, like newline and
+tab, is merely changed to exactly one space, with no special attempt to
+compress consecutive spaces. Each quote character: @kbd{"} is doubled
+so it will be correctly processed by @command{nroff} or @command{troff}.
+
+@item -T
+@itemx --format=tex
+
+Choose an output format suitable for @TeX{} processing. Each output
+line will look like:
+
+@smallexample
+\xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
+@end smallexample
+
+@noindent
+so it will be possible to write a @code{\xx} definition to take care of
+the output typesetting. Note that when references are not being
+produced, that is, neither option @option{-A} nor option @option{-r} is
+selected, the last parameter of each @code{\xx} call is inhibited.
+Option @option{-M} can be used to change @samp{xx} to another macro
+name.
+
+In this output format, some special characters, like @kbd{$}, @kbd{%},
+@kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
+backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
+backslash and a pair of dollar signs (to force mathematical mode). The
+backslash itself produces the sequence @code{\backslash@{@}}.
+Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
+@code{~\@{ @}} respectively. Other diacriticized characters of the
+underlying character set produce an appropriate @TeX{} sequence as far
+as possible. The other non-graphical characters, like newline and tab,
+and all other characters which are not part of @acronym{ASCII}, are merely
+changed to exactly one space, with no special attempt to compress
+consecutive spaces. Let me know how to improve this special character
+processing for @TeX{}.
+
+@end table
+
+
+@node Compatibility in ptx
+@subsection The @sc{gnu} extensions to @command{ptx}
+
+This version of @command{ptx} contains a few features which do not exist in
+System V @command{ptx}. These extra features are suppressed by using the
+@option{-G} command line option, unless overridden by other command line
+options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
+simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
+Here are the differences between this program and System V @command{ptx}.
+
+@itemize @bullet
+
+@item
+This program can read many input files at once, it always writes the
+resulting concordance on standard output. On the other hand, System V
+@command{ptx} reads only one file and sends the result to standard output
+or, if a second @var{file} parameter is given on the command, to that
+@var{file}.
+
+Having output parameters not introduced by options is a dangerous
+practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
+portably between @sc{gnu} and System V, you should always use it with a
+single input file, and always expect the result on standard output. You
+might also want to automatically configure in a @option{-G} option to
+@command{ptx} calls in products using @command{ptx}, if the configurator finds
+that the installed @command{ptx} accepts @option{-G}.
+
+@item
+The only options available in System V @command{ptx} are options @option{-b},
+@option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
+@option{-w}. All other options are @sc{gnu} extensions and are not repeated in
+this enumeration. Moreover, some options have a slightly different
+meaning when @sc{gnu} extensions are enabled, as explained below.
+
+@item
+By default, concordance output is not formatted for @command{troff} or
+@command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
+or @command{nroff} output may still be selected through option @option{-O}.
+
+@item
+Unless @option{-R} option is used, the maximum reference width is
+subtracted from the total output line width. With @sc{gnu} extensions
+disabled, width of references is not taken into account in the output
+line width computations.
+
+@item
+All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
+processed from input file with no adverse effect, even if @sc{gnu} extensions
+are disabled. However, System V @command{ptx} does not accept 8-bit characters,
+a few control characters are rejected, and the tilde @kbd{~} is also rejected.
+
+@item
+Input line length is only limited by available memory, even if @sc{gnu}
+extensions are disabled. However, System V @command{ptx} processes only
+the first 200 characters in each line.
+
+@item
+The break (non-word) characters default to be every character except all
+letters of the underlying character set, diacriticized or not. When @sc{gnu}
+extensions are disabled, the break characters default to space, tab and
+newline only.
+
+@item
+The program makes better use of output line width. If @sc{gnu} extensions
+are disabled, the program rather tries to imitate System V @command{ptx},
+but still, there are some slight disposition glitches this program does
+not completely reproduce.
+
+@item
+The user can specify both an Ignore file and an Only file. This is not
+allowed with System V @command{ptx}.
+
+@end itemize
+
+
+@node tsort invocation
+@section @command{tsort}: Topological sort
+
+@pindex tsort
+@cindex topological sort
+
+@command{tsort} performs a topological sort on the given @var{file}, or
+standard input if no input file is given or for a @var{file} of
+@samp{-}. For more details and some history, see @ref{tsort background}.
+Synopsis:
+
+@example
+tsort [@var{option}] [@var{file}]
+@end example
+
+@command{tsort} reads its input as pairs of strings, separated by blanks,
+indicating a partial ordering. The output is a total ordering that
+corresponds to the given partial ordering.
+
+For example
+
+@example
+tsort <<EOF
+a b c
+d
+e f
+b c d e
+EOF
+@end example
+
+@noindent
+will produce the output
+
+@example
+a
+b
+c
+d
+e
+f
+@end example
+
+Consider a more realistic example.
+You have a large set of functions all in one file, and they may all be
+declared static except one. Currently that one (say @code{main}) is the
+first function defined in the file, and the ones it calls directly follow
+it, followed by those they call, etc. Let's say that you are determined
+to take advantage of prototypes, so you have to choose between declaring
+all of those functions (which means duplicating a lot of information from
+the definitions) and rearranging the functions so that as many as possible
+are defined before they are used. One way to automate the latter process
+is to get a list for each function of the functions it calls directly.
+Many programs can generate such lists. They describe a call graph.
+Consider the following list, in which a given line indicates that the
+function on the left calls the one on the right directly.
+
+@example
+main parse_options
+main tail_file
+main tail_forever
+tail_file pretty_name
+tail_file write_header
+tail_file tail
+tail_forever recheck
+tail_forever pretty_name
+tail_forever write_header
+tail_forever dump_remainder
+tail tail_lines
+tail tail_bytes
+tail_lines start_lines
+tail_lines dump_remainder
+tail_lines file_lines
+tail_lines pipe_lines
+tail_bytes xlseek
+tail_bytes start_bytes
+tail_bytes dump_remainder
+tail_bytes pipe_bytes
+file_lines dump_remainder
+recheck pretty_name
+@end example
+
+then you can use @command{tsort} to produce an ordering of those
+functions that satisfies your requirement.
+
+@example
+example$ tsort call-graph | tac
+dump_remainder
+start_lines
+file_lines
+pipe_lines
+xlseek
+start_bytes
+pipe_bytes
+tail_lines
+tail_bytes
+pretty_name
+write_header
+tail
+recheck
+parse_options
+tail_file
+tail_forever
+main
+@end example
+
+@command{tsort} detects any cycles in the input and writes the first cycle
+encountered to standard error.
+
+Note that for a given partial ordering, generally there is no unique
+total ordering. In the context of the call graph above, the function
+@code{parse_options} may be placed anywhere in the list as long as it
+precedes @code{main}.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+@menu
+* tsort background:: Where tsort came from.
+@end menu
+
+@node tsort background
+@subsection @command{tsort}: Background
+
+@command{tsort} exists because very early versions of the Unix linker processed
+an archive file exactly once, and in order. As @command{ld} read each object
+in the archive, it decided whether it was needed in the program based on
+whether it defined any symbols which were undefined at that point in
+the link.
+
+This meant that dependencies within the archive had to be handled
+specially. For example, @code{scanf} probably calls @code{read}. That means
+that in a single pass through an archive, it was important for @code{scanf.o}
+to appear before read.o, because otherwise a program which calls
+@code{scanf} but not @code{read} might end up with an unexpected unresolved
+reference to @code{read}.
+
+The way to address this problem was to first generate a set of
+dependencies of one object file on another. This was done by a shell
+script called @command{lorder}. The GNU tools don't provide a version of
+lorder, as far as I know, but you can still find it in BSD
+distributions.
+
+Then you ran @command{tsort} over the @command{lorder} output, and you used the
+resulting sort to define the order in which you added objects to the archive.
+
+This whole procedure has been obsolete since about 1980, because
+Unix archives now contain a symbol table (traditionally built by
+@command{ranlib}, now generally built by @command{ar} itself), and the Unix
+linker uses the symbol table to effectively make multiple passes over
+an archive file.
+
+Anyhow, that's where tsort came from. To solve an old problem with
+the way the linker handled archive files, which has since been solved
+in different ways.
+
+
+@node Operating on fields within a line
+@chapter Operating on fields within a line
+
+@menu
+* cut invocation:: Print selected parts of lines.
+* paste invocation:: Merge lines of files.
+* join invocation:: Join lines on a common field.
+@end menu
+
+
+@node cut invocation
+@section @command{cut}: Print selected parts of lines
+
+@pindex cut
+@command{cut} writes to standard output selected parts of each line of each
+input file, or standard input if no files are given or for a file name of
+@samp{-}. Synopsis:
+
+@example
+cut @var{option}@dots{} [@var{file}]@dots{}
+@end example
+
+In the table which follows, the @var{byte-list}, @var{character-list},
+and @var{field-list} are one or more numbers or ranges (two numbers
+separated by a dash) separated by commas. Bytes, characters, and
+fields are numbered starting at 1. Incomplete ranges may be
+given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
+@samp{@var{n}} through end of line or last field. The list elements
+can be repeated, can overlap, and can be specified in any order; but
+the selected input is written in the same order that it is read, and
+is written exactly once.
+
+The program accepts the following options. Also see @ref{Common
+options}.
+
+@table @samp
+
+@item -b @var{byte-list}
+@itemx --bytes=@var{byte-list}
+@opindex -b
+@opindex --bytes
+Select for printing only the bytes in positions listed in
+@var{byte-list}. Tabs and backspaces are treated like any other
+character; they take up 1 byte. If an output delimiter is specified,
+(see the description of @option{--output-delimiter}), then output that
+string between ranges of selected bytes.
+
+@item -c @var{character-list}
+@itemx --characters=@var{character-list}
+@opindex -c
+@opindex --characters
+Select for printing only the characters in positions listed in
+@var{character-list}. The same as @option{-b} for now, but
+internationalization will change that. Tabs and backspaces are
+treated like any other character; they take up 1 character. If an
+output delimiter is specified, (see the description of
+@option{--output-delimiter}), then output that string between ranges
+of selected bytes.
+
+@item -f @var{field-list}
+@itemx --fields=@var{field-list}
+@opindex -f
+@opindex --fields
+Select for printing only the fields listed in @var{field-list}.
+Fields are separated by a TAB character by default. Also print any
+line that contains no delimiter character, unless the
+@option{--only-delimited} (@option{-s}) option is specified
+
+@item -d @var{input_delim_byte}
+@itemx --delimiter=@var{input_delim_byte}
+@opindex -d
+@opindex --delimiter
+With @option{-f}, use the first byte of @var{input_delim_byte} as
+the input fields separator (default is TAB).
+
+@item -n
+@opindex -n
+Do not split multi-byte characters (no-op for now).
+
+@item -s
+@itemx --only-delimited
+@opindex -s
+@opindex --only-delimited
+For @option{-f}, do not print lines that do not contain the field separator
+character. Normally, any line without a field separator is printed verbatim.
+
+@item --output-delimiter=@var{output_delim_string}
+@opindex --output-delimiter
+With @option{-f}, output fields are separated by @var{output_delim_string}.
+The default with @option{-f} is to use the input delimiter.
+When using @option{-b} or @option{-c} to select ranges of byte or
+character offsets (as opposed to ranges of fields),
+output @var{output_delim_string} between non-overlapping
+ranges of selected bytes.
+
+@item --complement
+@opindex --complement
+This option is a @acronym{GNU} extension.
+Select for printing the complement of the bytes, characters or fields
+selected with the @option{-b}, @option{-c} or @option{-f} options.
+In other words, do @emph{not} print the bytes, characters or fields
+specified via those options. This option is useful when you have
+many fields and want to print all but a few of them.
+
+@end table
+
+@exitstatus
+
+
+@node paste invocation
+@section @command{paste}: Merge lines of files
+
+@pindex paste
+@cindex merging files
+
+@command{paste} writes to standard output lines consisting of sequentially
+corresponding lines of each given file, separated by a TAB character.
+Standard input is used for a file name of @samp{-} or if no input files
+are given.
+
+For example:
+
+@example
+$ cat num2
+1
+2
+$ cat let3
+a
+b
+c
+$ paste num2 let3
+1 a
+2 b
+ @ c
+@end example
+
+Synopsis:
+
+@example
+paste [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -s
+@itemx --serial
+@opindex -s
+@opindex --serial
+Paste the lines of one file at a time rather than one line from each
+file. Using the above example data:
+
+@example
+$ paste -s num2 let3
+1 2
+a b c
+@end example
+
+@item -d @var{delim-list}
+@itemx --delimiters=@var{delim-list}
+@opindex -d
+@opindex --delimiters
+Consecutively use the characters in @var{delim-list} instead of
+TAB to separate merged lines. When @var{delim-list} is
+exhausted, start again at its beginning. Using the above example data:
+
+@example
+$ paste -d '%_' num2 let3 num2
+1%a_1
+2%b_2
+%c_
+@end example
+
+@end table
+
+@exitstatus
+
+
+@node join invocation
+@section @command{join}: Join lines on a common field
+
+@pindex join
+@cindex common field, joining on
+
+@command{join} writes to standard output a line for each pair of input
+lines that have identical join fields. Synopsis:
+
+@example
+join [@var{option}]@dots{} @var{file1} @var{file2}
+@end example
+
+Either @var{file1} or @var{file2} (but not both) can be @samp{-},
+meaning standard input. @var{file1} and @var{file2} should be
+sorted on the join fields.
+
+@vindex LC_COLLATE
+Normally, the sort order is that of the
+collating sequence specified by the @env{LC_COLLATE} locale. Unless
+the @option{-t} option is given, the sort comparison ignores blanks at
+the start of the join field, as in @code{sort -b}. If the
+@option{--ignore-case} option is given, the sort comparison ignores
+the case of characters in the join field, as in @code{sort -f}.
+
+The @command{sort} and @command{join} commands should use consistent
+locales and options if the output of @command{sort} is fed to
+@command{join}. You can use a command like @samp{sort -k 1b,1} to
+sort a file on its default join field, but if you select a non-default
+locale, join field, separator, or comparison options, then you should
+do so consistently between @command{join} and @command{sort}.
+
+If the input has no unpairable lines, a @acronym{GNU} extension is
+available; the sort order can be any order that considers two fields
+to be equal if and only if the sort comparison described above
+considers them to be equal. For example:
+
+@example
+$ cat file1
+a a1
+c c1
+b b1
+$ cat file2
+a a2
+c c2
+b b2
+$ join file1 file2
+a a1 a2
+c c1 c2
+b b1 b2
+@end example
+
+@checkOrderOption{join}
+
+The defaults are:
+@itemize
+@item the join field is the first field in each line;
+@item fields in the input are separated by one or more blanks, with leading
+blanks on the line ignored;
+@item fields in the output are separated by a space;
+@item each output line consists of the join field, the remaining
+fields from @var{file1}, then the remaining fields from @var{file2}.
+@end itemize
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a @var{file-number}
+@opindex -a
+Print a line for each unpairable line in file @var{file-number} (either
+@samp{1} or @samp{2}), in addition to the normal output.
+
+@item --check-order
+Fail with an error message if either input file is wrongly ordered.
+
+@item --nocheck-order
+Do not check that both input files are in sorted order. This is the default.
+
+@item -e @var{string}
+@opindex -e
+Replace those output fields that are missing in the input with
+@var{string}.
+
+@item -i
+@itemx --ignore-case
+@opindex -i
+@opindex --ignore-case
+Ignore differences in case when comparing keys.
+With this option, the lines of the input files must be ordered in the same way.
+Use @samp{sort -f} to produce this ordering.
+
+@item -1 @var{field}
+@opindex -1
+Join on field @var{field} (a positive integer) of file 1.
+
+@item -2 @var{field}
+@opindex -2
+Join on field @var{field} (a positive integer) of file 2.
+
+@item -j @var{field}
+Equivalent to @option{-1 @var{field} -2 @var{field}}.
+
+@item -o @var{field-list}
+Construct each output line according to the format in @var{field-list}.
+Each element in @var{field-list} is either the single character @samp{0} or
+has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
+@samp{2} and @var{n} is a positive field number.
+
+A field specification of @samp{0} denotes the join field.
+In most cases, the functionality of the @samp{0} field spec
+may be reproduced using the explicit @var{m.n} that corresponds
+to the join field. However, when printing unpairable lines
+(using either of the @option{-a} or @option{-v} options), there is no way
+to specify the join field using @var{m.n} in @var{field-list}
+if there are unpairable lines in both files.
+To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
+field specification notation.
+
+The elements in @var{field-list}
+are separated by commas or blanks.
+Blank separators typically need to be quoted for the shell. For
+example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
+2.2'} are equivalent.
+
+All output lines---including those printed because of any -a or -v
+option---are subject to the specified @var{field-list}.
+
+@item -t @var{char}
+Use character @var{char} as the input and output field separator.
+Treat as significant each occurrence of @var{char} in the input file.
+Use @samp{sort -t @var{char}}, without the @option{-b} option of
+@samp{sort}, to produce this ordering.
+
+@item -v @var{file-number}
+Print a line for each unpairable line in file @var{file-number}
+(either @samp{1} or @samp{2}), instead of the normal output.
+
+@end table
+
+@exitstatus
+
+
+@node Operating on characters
+@chapter Operating on characters
+
+@cindex operating on characters
+
+This commands operate on individual characters.
+
+@menu
+* tr invocation:: Translate, squeeze, and/or delete characters.
+* expand invocation:: Convert tabs to spaces.
+* unexpand invocation:: Convert spaces to tabs.
+@end menu
+
+
+@node tr invocation
+@section @command{tr}: Translate, squeeze, and/or delete characters
+
+@pindex tr
+
+Synopsis:
+
+@example
+tr [@var{option}]@dots{} @var{set1} [@var{set2}]
+@end example
+
+@command{tr} copies standard input to standard output, performing
+one of the following operations:
+
+@itemize @bullet
+@item
+translate, and optionally squeeze repeated characters in the result,
+@item
+squeeze repeated characters,
+@item
+delete characters,
+@item
+delete characters, then squeeze repeated characters from the result.
+@end itemize
+
+The @var{set1} and (if given) @var{set2} arguments define ordered
+sets of characters, referred to below as @var{set1} and @var{set2}. These
+sets are the characters of the input that @command{tr} operates on.
+The @option{--complement} (@option{-c}, @option{-C}) option replaces
+@var{set1} with its
+complement (all of the characters that are not in @var{set1}).
+
+Currently @command{tr} fully supports only single-byte characters.
+Eventually it will support multibyte characters; when it does, the
+@option{-C} option will cause it to complement the set of characters,
+whereas @option{-c} will cause it to complement the set of values.
+This distinction will matter only when some values are not characters,
+and this is possible only in locales using multibyte encodings when
+the input contains encoding errors.
+
+The program accepts the @option{--help} and @option{--version}
+options. @xref{Common options}. Options must precede operands.
+
+@exitstatus
+
+@menu
+* Character sets:: Specifying sets of characters.
+* Translating:: Changing one set of characters to another.
+* Squeezing:: Squeezing repeats and deleting.
+@end menu
+
+
+@node Character sets
+@subsection Specifying sets of characters
+
+@cindex specifying sets of characters
+
+The format of the @var{set1} and @var{set2} arguments resembles
+the format of regular expressions; however, they are not regular
+expressions, only lists of characters. Most characters simply
+represent themselves in these strings, but the strings can contain
+the shorthands listed below, for convenience. Some of them can be
+used only in @var{set1} or @var{set2}, as noted below.
+
+@table @asis
+
+@item Backslash escapes
+@cindex backslash escapes
+
+The following backslash escape sequences are recognized:
+
+@table @samp
+@item \a
+Control-G.
+@item \b
+Control-H.
+@item \f
+Control-L.
+@item \n
+Control-J.
+@item \r
+Control-M.
+@item \t
+Control-I.
+@item \v
+Control-K.
+@item \@var{ooo}
+The character with the value given by @var{ooo}, which is 1 to 3
+octal digits,
+@item \\
+A backslash.
+@end table
+
+While a backslash followed by a character not listed above is
+interpreted as that character, the backslash also effectively
+removes any special significance, so it is useful to escape
+@samp{[}, @samp{]}, @samp{*}, and @samp{-}.
+
+@item Ranges
+@cindex ranges
+
+The notation @samp{@var{m}-@var{n}} expands to all of the characters
+from @var{m} through @var{n}, in ascending order. @var{m} should
+collate before @var{n}; if it doesn't, an error results. As an example,
+@samp{0-9} is the same as @samp{0123456789}.
+
+@sc{gnu} @command{tr} does not support the System V syntax that uses square
+brackets to enclose ranges. Translations specified in that format
+sometimes work as expected, since the brackets are often transliterated
+to themselves. However, they should be avoided because they sometimes
+behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
+as well as digits.
+
+Many historically common and even accepted uses of ranges are not
+portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
+range will not do what most would expect because @samp{A} through @samp{Z}
+are not contiguous as they are in @acronym{ASCII}.
+If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
+the best way to work around this is to use character classes (see below).
+Otherwise, it is most portable (and most ugly) to enumerate the members
+of the ranges.
+
+@item Repeated characters
+@cindex repeated characters
+
+The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
+copies of character @var{c}. Thus, @samp{[y*6]} is the same as
+@samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
+to as many copies of @var{c} as are needed to make @var{set2} as long as
+@var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
+octal, otherwise in decimal.
+
+@item Character classes
+@cindex character classes
+
+The notation @samp{[:@var{class}:]} expands to all of the characters in
+the (predefined) class @var{class}. The characters expand in no
+particular order, except for the @code{upper} and @code{lower} classes,
+which expand in ascending order. When the @option{--delete} (@option{-d})
+and @option{--squeeze-repeats} (@option{-s}) options are both given, any
+character class can be used in @var{set2}. Otherwise, only the
+character classes @code{lower} and @code{upper} are accepted in
+@var{set2}, and then only if the corresponding character class
+(@code{upper} and @code{lower}, respectively) is specified in the same
+relative position in @var{set1}. Doing this specifies case conversion.
+The class names are given below; an error results when an invalid class
+name is given.
+
+@table @code
+@item alnum
+@opindex alnum
+Letters and digits.
+@item alpha
+@opindex alpha
+Letters.
+@item blank
+@opindex blank
+Horizontal whitespace.
+@item cntrl
+@opindex cntrl
+Control characters.
+@item digit
+@opindex digit
+Digits.
+@item graph
+@opindex graph
+Printable characters, not including space.
+@item lower
+@opindex lower
+Lowercase letters.
+@item print
+@opindex print
+Printable characters, including space.
+@item punct
+@opindex punct
+Punctuation characters.
+@item space
+@opindex space
+Horizontal or vertical whitespace.
+@item upper
+@opindex upper
+Uppercase letters.
+@item xdigit
+@opindex xdigit
+Hexadecimal digits.
+@end table
+
+@item Equivalence classes
+@cindex equivalence classes
+
+The syntax @samp{[=@var{c}=]} expands to all of the characters that are
+equivalent to @var{c}, in no particular order. Equivalence classes are
+a relatively recent invention intended to support non-English alphabets.
+But there seems to be no standard way to define them or determine their
+contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
+each character's equivalence class consists only of that character,
+which is of no particular use.
+
+@end table
+
+
+@node Translating
+@subsection Translating
+
+@cindex translating characters
+
+@command{tr} performs translation when @var{set1} and @var{set2} are
+both given and the @option{--delete} (@option{-d}) option is not given.
+@command{tr} translates each character of its input that is in @var{set1}
+to the corresponding character in @var{set2}. Characters not in
+@var{set1} are passed through unchanged. When a character appears more
+than once in @var{set1} and the corresponding characters in @var{set2}
+are not all the same, only the final one is used. For example, these
+two commands are equivalent:
+
+@example
+tr aaa xyz
+tr a z
+@end example
+
+A common use of @command{tr} is to convert lowercase characters to
+uppercase. This can be done in many ways. Here are three of them:
+
+@example
+tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
+tr a-z A-Z
+tr '[:lower:]' '[:upper:]'
+@end example
+
+@noindent
+But note that using ranges like @code{a-z} above is not portable.
+
+When @command{tr} is performing translation, @var{set1} and @var{set2}
+typically have the same length. If @var{set1} is shorter than
+@var{set2}, the extra characters at the end of @var{set2} are ignored.
+
+On the other hand, making @var{set1} longer than @var{set2} is not
+portable; @acronym{POSIX} says that the result is undefined. In this situation,
+BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
+the last character of @var{set2} as many times as necessary. System V
+@command{tr} truncates @var{set1} to the length of @var{set2}.
+
+By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
+When the @option{--truncate-set1} (@option{-t}) option is given,
+@sc{gnu} @command{tr} handles this case like the System V @command{tr}
+instead. This option is ignored for operations other than translation.
+
+Acting like System V @command{tr} in this case breaks the relatively common
+BSD idiom:
+
+@example
+tr -cs A-Za-z0-9 '\012'
+@end example
+
+@noindent
+because it converts only zero bytes (the first element in the
+complement of @var{set1}), rather than all non-alphanumerics, to
+newlines.
+
+@noindent
+By the way, the above idiom is not portable because it uses ranges, and
+it assumes that the octal code for newline is 012.
+Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
+
+@example
+tr -cs '[:alnum:]' '[\n*]'
+@end example
+
+
+@node Squeezing
+@subsection Squeezing repeats and deleting
+
+@cindex squeezing repeat characters
+@cindex deleting characters
+
+When given just the @option{--delete} (@option{-d}) option, @command{tr}
+removes any input characters that are in @var{set1}.
+
+When given just the @option{--squeeze-repeats} (@option{-s}) option,
+@command{tr} replaces each input sequence of a repeated character that
+is in @var{set1} with a single occurrence of that character.
+
+When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
+first performs any deletions using @var{set1}, then squeezes repeats
+from any remaining characters using @var{set2}.
+
+The @option{--squeeze-repeats} option may also be used when translating,
+in which case @command{tr} first performs translation, then squeezes
+repeats from any remaining characters using @var{set2}.
+
+Here are some examples to illustrate various combinations of options:
+
+@itemize @bullet
+
+@item
+Remove all zero bytes:
+
+@example
+tr -d '\0'
+@end example
+
+@item
+Put all words on lines by themselves. This converts all
+non-alphanumeric characters to newlines, then squeezes each string
+of repeated newlines into a single newline:
+
+@example
+tr -cs '[:alnum:]' '[\n*]'
+@end example
+
+@item
+Convert each sequence of repeated newlines to a single newline:
+
+@example
+tr -s '\n'
+@end example
+
+@item
+Find doubled occurrences of words in a document.
+@c Separate the following two "the"s, so typo checkers don't complain.
+For example, people often write ``the @w{}the'' with the repeated words
+separated by a newline. The Bourne shell script below works first
+by converting each sequence of punctuation and blank characters to a
+single newline. That puts each ``word'' on a line by itself.
+Next it maps all uppercase characters to lower case, and finally it
+runs @command{uniq} with the @option{-d} option to print out only the words
+that were repeated.
+
+@example
+#!/bin/sh
+cat -- "$@@" \
+ | tr -s '[:punct:][:blank:]' '[\n*]' \
+ | tr '[:upper:]' '[:lower:]' \
+ | uniq -d
+@end example
+
+@item
+Deleting a small set of characters is usually straightforward. For example,
+to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
+
+@example
+tr -d axM
+@end example
+
+However, when @samp{-} is one of those characters, it can be tricky because
+@samp{-} has special meanings. Performing the same task as above but also
+removing all @samp{-} characters, we might try @code{tr -d -axM}, but
+that would fail because @command{tr} would try to interpret @option{-a} as
+a command-line option. Alternatively, we could try putting the hyphen
+inside the string, @code{tr -d a-xM}, but that wouldn't work either because
+it would make @command{tr} interpret @code{a-x} as the range of characters
+@samp{a}@dots{}@samp{x} rather than the three.
+One way to solve the problem is to put the hyphen at the end of the list
+of characters:
+
+@example
+tr -d axM-
+@end example
+
+Or you can use @samp{--} to terminate option processing:
+
+@example
+tr -d -- -axM
+@end example
+
+More generally, use the character class notation @code{[=c=]}
+with @samp{-} (or any other character) in place of the @samp{c}:
+
+@example
+tr -d '[=-=]axM'
+@end example
+
+Note how single quotes are used in the above example to protect the
+square brackets from interpretation by a shell.
+
+@end itemize
+
+
+@node expand invocation
+@section @command{expand}: Convert tabs to spaces
+
+@pindex expand
+@cindex tabs to spaces, converting
+@cindex converting tabs to spaces
+
+@command{expand} writes the contents of each given @var{file}, or standard
+input if none are given or for a @var{file} of @samp{-}, to standard
+output, with tab characters converted to the appropriate number of
+spaces. Synopsis:
+
+@example
+expand [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @command{expand} converts all tabs to spaces. It preserves
+backspace characters in the output; they decrement the column count for
+tab calculations. The default action is equivalent to @option{-t 8} (set
+tabs every 8 columns).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -t @var{tab1}[,@var{tab2}]@dots{}
+@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
+@opindex -t
+@opindex --tabs
+@cindex tab stops, setting
+If only one tab stop is given, set the tabs @var{tab1} spaces apart
+(default is 8). Otherwise, set the tabs at columns @var{tab1},
+@var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
+last tab stop given with single spaces. Tab stops can be separated by
+blanks as well as by commas.
+
+For compatibility, GNU @command{expand} also accepts the obsolete
+option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
+should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
+
+@item -i
+@itemx --initial
+@opindex -i
+@opindex --initial
+@cindex initial tabs, converting
+Only convert initial tabs (those that precede all non-space or non-tab
+characters) on each line to spaces.
+
+@end table
+
+@exitstatus
+
+
+@node unexpand invocation
+@section @command{unexpand}: Convert spaces to tabs
+
+@pindex unexpand
+
+@command{unexpand} writes the contents of each given @var{file}, or
+standard input if none are given or for a @var{file} of @samp{-}, to
+standard output, converting blanks at the beginning of each line into
+as many tab characters as needed. In the default @acronym{POSIX}
+locale, a @dfn{blank} is a space or a tab; other locales may specify
+additional blank characters. Synopsis:
+
+@example
+unexpand [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+By default, @command{unexpand} converts only initial blanks (those
+that precede all non-blank characters) on each line. It
+preserves backspace characters in the output; they decrement the column
+count for tab calculations. By default, tabs are set at every 8th
+column.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -t @var{tab1}[,@var{tab2}]@dots{}
+@itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
+@opindex -t
+@opindex --tabs
+If only one tab stop is given, set the tabs @var{tab1} columns apart
+instead of the default 8. Otherwise, set the tabs at columns
+@var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
+beyond the tab stops given unchanged. Tab stops can be separated by
+blanks as well as by commas. This option implies the @option{-a} option.
+
+For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
+@option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
+separated by commas. (Unlike @option{-t}, this obsolete option does
+not imply @option{-a}.) New scripts should use @option{--first-only -t
+@var{tab1}[,@var{tab2}]@dots{}} instead.
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Also convert all sequences of two or more blanks just before a tab stop,
+even if they occur after non-blank characters in a line.
+
+@end table
+
+@exitstatus
+
+
+@node Directory listing
+@chapter Directory listing
+
+This chapter describes the @command{ls} command and its variants @command{dir}
+and @command{vdir}, which list information about files.
+
+@menu
+* ls invocation:: List directory contents.
+* dir invocation:: Briefly ls.
+* vdir invocation:: Verbosely ls.
+* dircolors invocation:: Color setup for ls, etc.
+@end menu
+
+
+@node ls invocation
+@section @command{ls}: List directory contents
+
+@pindex ls
+@cindex directory listing
+
+The @command{ls} program lists information about files (of any type,
+including directories). Options and file arguments can be intermixed
+arbitrarily, as usual.
+
+For non-option command-line arguments that are directories, by default
+@command{ls} lists the contents of directories, not recursively, and
+omitting files with names beginning with @samp{.}. For other non-option
+arguments, by default @command{ls} lists just the file name. If no
+non-option argument is specified, @command{ls} operates on the current
+directory, acting as if it had been invoked with a single argument of @samp{.}.
+
+@vindex LC_ALL
+By default, the output is sorted alphabetically, according to the locale
+settings in effect.@footnote{If you use a non-@acronym{POSIX}
+locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
+produce output that is sorted differently than you're accustomed to.
+In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
+If standard output is
+a terminal, the output is in columns (sorted vertically) and control
+characters are output as question marks; otherwise, the output is listed
+one per line and control characters are output as-is.
+
+Because @command{ls} is such a fundamental program, it has accumulated many
+options over the years. They are described in the subsections below;
+within each section, options are listed alphabetically (ignoring case).
+The division of options into the subsections is not absolute, since some
+options affect more than one aspect of @command{ls}'s operation.
+
+@cindex exit status of @command{ls}
+Exit status:
+
+@display
+0 success
+1 minor problems (e.g., failure to access a file or directory not
+ specified as a command line argument. This happens when listing a
+ directory in which entries are actively being removed or renamed.)
+2 serious trouble (e.g., memory exhausted, invalid option or failure
+ to access file or directory specified as a command line argument)
+@end display
+
+Also see @ref{Common options}.
+
+@menu
+* Which files are listed::
+* What information is listed::
+* Sorting the output::
+* More details about version sort::
+* General output formatting::
+* Formatting file timestamps::
+* Formatting the file names::
+@end menu
+
+
+@node Which files are listed
+@subsection Which files are listed
+
+These options determine which files @command{ls} lists information for.
+By default, @command{ls} lists files and the contents of any
+directories on the command line, except that in directories it ignores
+files whose names start with @samp{.}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+In directories, do not ignore file names that start with @samp{.}.
+
+@item -A
+@itemx --almost-all
+@opindex -A
+@opindex --almost-all
+In directories, do not ignore all file names that start with @samp{.};
+ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
+option overrides this option.
+
+@item -B
+@itemx --ignore-backups
+@opindex -B
+@opindex --ignore-backups
+@cindex backup files, ignoring
+In directories, ignore files that end with @samp{~}. This option is
+equivalent to @samp{--ignore='*~' --ignore='.*~'}.
+
+@item -d
+@itemx --directory
+@opindex -d
+@opindex --directory
+List just the names of directories, as with other types of files, rather
+than listing their contents.
+@c The following sentence is the same as the one for -F.
+Do not follow symbolic links listed on the
+command line unless the @option{--dereference-command-line} (@option{-H}),
+@option{--dereference} (@option{-L}), or
+@option{--dereference-command-line-symlink-to-dir} options are specified.
+
+@item -H
+@itemx --dereference-command-line
+@opindex -H
+@opindex --dereference-command-line
+@cindex symbolic links, dereferencing
+If a command line argument specifies a symbolic link, show information
+for the file the link references rather than for the link itself.
+
+@itemx --dereference-command-line-symlink-to-dir
+@opindex --dereference-command-line-symlink-to-dir
+@cindex symbolic links, dereferencing
+Do not dereference symbolic links, with one exception:
+if a command line argument specifies a symbolic link that refers to
+a directory, show information for that directory rather than for the
+link itself.
+This is the default behavior when no other dereferencing-related
+option has been specified (@option{--classify} (@option{-F}),
+@option{--directory} (@option{-d}),
+(@option{-l}),
+@option{--dereference} (@option{-L}), or
+@option{--dereference-command-line} (@option{-H})).
+
+@item --group-directories-first
+@opindex --group-directories-first
+Group all the directories before the files and then sort the
+directories and the files separately using the selected sort key
+(see --sort option).
+That is, this option specifies a primary sort key,
+and the --sort option specifies a secondary key.
+However, any use of @option{--sort=none}
+(@option{-U}) disables this option altogether.
+
+@item --hide=PATTERN
+@opindex --hide=@var{pattern}
+In directories, ignore files whose names match the shell pattern
+@var{pattern}, unless the @option{--all} (@option{-a}) or
+@option{--almost-all} (@option{-A}) is also given. This
+option acts like @option{--ignore=@var{pattern}} except that it has no
+effect if @option{--all} (@option{-a}) or @option{--almost-all}
+(@option{-A}) is also given.
+
+This option can be useful in shell aliases. For example, if
+@command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
+an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
+lists the file @file{README~} even though @samp{ly -A} would not.
+
+@item -I @var{pattern}
+@itemx --ignore=@var{pattern}
+@opindex -I
+@opindex --ignore=@var{pattern}
+In directories, ignore files whose names match the shell pattern
+(not regular expression) @var{pattern}. As
+in the shell, an initial @samp{.} in a file name does not match a
+wildcard at the start of @var{pattern}. Sometimes it is useful
+to give this option several times. For example,
+
+@smallexample
+$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
+@end smallexample
+
+The first option ignores names of length 3 or more that start with @samp{.},
+the second ignores all two-character names that start with @samp{.}
+except @samp{..}, and the third ignores names that start with @samp{#}.
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+@cindex symbolic links, dereferencing
+When showing file information for a symbolic link, show information
+for the file the link references rather than the link itself.
+However, even with this option, @command{ls} still prints the name
+of the link itself, not the name of the file that the link points to.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursive directory listing
+@cindex directory listing, recursive
+List the contents of all directories recursively.
+
+@end table
+
+
+@node What information is listed
+@subsection What information is listed
+
+These options affect the information that @command{ls} displays. By
+default, only file names are shown.
+
+@table @samp
+
+@item --author
+@opindex --author
+@cindex hurd, author, printing
+List each file's author when producing long format directory listings.
+In GNU/Hurd, file authors can differ from their owners, but in other
+operating systems the two are the same.
+
+@item -D
+@itemx --dired
+@opindex -D
+@opindex --dired
+@cindex dired Emacs mode support
+With the long listing (@option{-l}) format, print an additional line after
+the main output:
+
+@example
+//DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
+@end example
+
+@noindent
+The @var{begn} and @var{endn} are unsigned integers that record the
+byte position of the beginning and end of each file name in the output.
+This makes it easy for Emacs to find the names, even when they contain
+unusual characters such as space or newline, without fancy searching.
+
+If directories are being listed recursively (@option{-R}), output a similar
+line with offsets for each subdirectory name:
+
+@example
+//SUBDIRED// @var{beg1} @var{end1} @dots{}
+@end example
+
+Finally, output a line of the form:
+
+@example
+//DIRED-OPTIONS// --quoting-style=@var{word}
+@end example
+
+@noindent
+where @var{word} is the quoting style (@pxref{Formatting the file names}).
+
+Here is an actual example:
+
+@example
+$ mkdir -p a/sub/deeper a/sub2
+$ touch a/f1 a/f2
+$ touch a/sub/deeper/file
+$ ls -gloRF --dired a
+ a:
+ total 8
+ -rw-r--r-- 1 0 Jun 10 12:27 f1
+ -rw-r--r-- 1 0 Jun 10 12:27 f2
+ drwxr-xr-x 3 4096 Jun 10 12:27 sub/
+ drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
+
+ a/sub:
+ total 4
+ drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
+
+ a/sub/deeper:
+ total 0
+ -rw-r--r-- 1 0 Jun 10 12:27 file
+
+ a/sub2:
+ total 0
+//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
+//SUBDIRED// 2 3 167 172 228 240 290 296
+//DIRED-OPTIONS// --quoting-style=literal
+@end example
+
+Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
+these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
+@file{file}.
+The offsets on the @samp{//SUBDIRED//} line delimit the following
+directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
+
+Here is an example of how to extract the fifth entry name, @samp{deeper},
+corresponding to the pair of offsets, 222 and 228:
+
+@example
+$ ls -gloRF --dired a > out
+$ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
+deeper
+@end example
+
+Note that although the listing above includes a trailing slash
+for the @samp{deeper} entry, the offsets select the name without
+the trailing slash. However, if you invoke @command{ls} with @option{--dired}
+along with an option like @option{--escape} (aka @option{-b}) and operate
+on a file whose name contains special characters, notice that the backslash
+@emph{is} included:
+
+@example
+$ touch 'a b'
+$ ls -blog --dired 'a b'
+ -rw-r--r-- 1 0 Jun 10 12:28 a\ b
+//DIRED// 30 34
+//DIRED-OPTIONS// --quoting-style=escape
+@end example
+
+If you use a quoting style that adds quote marks
+(e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
+So beware that the user may select the quoting style via the environment
+variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
+should either specify an explicit @option{--quoting-style=literal} option
+(aka @option{-N} or @option{--literal}) on the command line, or else be
+prepared to parse the escaped names.
+
+@item --full-time
+@opindex --full-time
+Produce long format directory listings, and list times in full. It is
+equivalent to using @option{--format=long} with
+@option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
+
+@item -g
+@opindex -g
+Produce long format directory listings, but don't display owner information.
+
+@item -G
+@itemx --no-group
+@opindex -G
+@opindex --no-group
+Inhibit display of group information in a long format directory listing.
+(This is the default in some non-@sc{gnu} versions of @command{ls}, so we
+provide this option for compatibility.)
+
+@optHumanReadable
+
+@item -i
+@itemx --inode
+@opindex -i
+@opindex --inode
+@cindex inode number, printing
+Print the inode number (also called the file serial number and index
+number) of each file to the left of the file name. (This number
+uniquely identifies each file within a particular file system.)
+
+@item -l
+@itemx --format=long
+@itemx --format=verbose
+@opindex -l
+@opindex --format
+@opindex long ls @r{format}
+@opindex verbose ls @r{format}
+In addition to the name of each file, print the file type, file mode bits,
+number of hard links, owner name, group name, size, and
+timestamp (@pxref{Formatting file timestamps}), normally
+the modification time. Print question marks for information that
+cannot be determined.
+
+Normally the size is printed as a byte count without punctuation, but
+this can be overridden (@pxref{Block size}). For example, @option{-h}
+prints an abbreviated, human-readable count, and
+@samp{--block-size="'1"} prints a byte count with the thousands
+separator of the current locale.
+
+For each directory that is listed, preface the files with a line
+@samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
+for all files in that directory. The block size currently defaults to 1024
+bytes, but this can be overridden (@pxref{Block size}).
+The @var{blocks} computed counts each hard link separately;
+this is arguably a deficiency.
+
+The file type is one of the following characters:
+
+@c The commented-out entries are ones we're not sure about.
+
+@table @samp
+@item -
+regular file
+@item b
+block special file
+@item c
+character special file
+@item C
+high performance (``contiguous data'') file
+@item d
+directory
+@item D
+door (Solaris 2.5 and up)
+@c @item F
+@c semaphore, if this is a distinct file type
+@item l
+symbolic link
+@c @item m
+@c multiplexed file (7th edition Unix; obsolete)
+@item M
+off-line (``migrated'') file (Cray DMF)
+@item n
+network special file (HP-UX)
+@item p
+FIFO (named pipe)
+@item P
+port (Solaris 10 and up)
+@c @item Q
+@c message queue, if this is a distinct file type
+@item s
+socket
+@c @item S
+@c shared memory object, if this is a distinct file type
+@c @item T
+@c typed memory object, if this is a distinct file type
+@c @item w
+@c whiteout (4.4BSD; not implemented)
+@item ?
+some other file type
+@end table
+
+@cindex permissions, output by @command{ls}
+The file mode bits listed are similar to symbolic mode specifications
+(@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
+third character of each set of permissions as follows:
+
+@table @samp
+@item s
+If the set-user-ID or set-group-ID bit and the corresponding executable bit
+are both set.
+
+@item S
+If the set-user-ID or set-group-ID bit is set but the corresponding
+executable bit is not set.
+
+@item t
+If the restricted deletion flag or sticky bit, and the
+other-executable bit, are both set. The restricted deletion flag is
+another name for the sticky bit. @xref{Mode Structure}.
+
+@item T
+If the restricted deletion flag or sticky bit is set but the
+other-executable bit is not set.
+
+@item x
+If the executable bit is set and none of the above apply.
+
+@item -
+Otherwise.
+@end table
+
+Following the file mode bits is a single character that specifies
+whether an alternate access method such as an access control list
+applies to the file. When the character following the file mode bits is a
+space, there is no alternate access method. When it is a printing
+character, then there is such a method.
+
+GNU @command{ls} uses a @samp{.} character to indicate a file
+with an SELinux security context, but no other alternate access method.
+
+A file with any other combination of alternate access methods
+is marked with a @samp{+} character.
+
+@item -n
+@itemx --numeric-uid-gid
+@opindex -n
+@opindex --numeric-uid-gid
+@cindex numeric uid and gid
+@cindex numeric user and group IDs
+Produce long format directory listings, but
+display numeric user and group IDs instead of the owner and group names.
+
+@item -o
+@opindex -o
+Produce long format directory listings, but don't display group information.
+It is equivalent to using @option{--format=long} with @option{--no-group} .
+
+@item -s
+@itemx --size
+@opindex -s
+@opindex --size
+@cindex disk allocation
+@cindex size of files, reporting
+Print the disk allocation of each file to the left of the file name.
+This is the amount of disk space used by the file, which is usually a
+bit more than the file's size, but it can be less if the file has holes.
+
+Normally the disk allocation is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+
+@cindex NFS mounts from BSD to HP-UX
+For files that are NFS-mounted from an HP-UX system to a BSD system,
+this option reports sizes that are half the correct values. On HP-UX
+systems, it reports sizes that are twice the correct values for files
+that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
+it also affects the HP-UX @command{ls} program.
+
+@optSi
+
+@end table
+
+
+@node Sorting the output
+@subsection Sorting the output
+
+@cindex sorting @command{ls} output
+These options change the order in which @command{ls} sorts the information
+it outputs. By default, sorting is done by character code
+(e.g., @acronym{ASCII} order).
+
+@table @samp
+
+@item -c
+@itemx --time=ctime
+@itemx --time=status
+@opindex -c
+@opindex --time
+@opindex ctime@r{, printing or sorting by}
+@opindex status time@r{, printing or sorting by}
+@opindex use time@r{, printing or sorting files by}
+If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
+print the status change time (the @samp{ctime} in the inode) instead of
+the modification time.
+When explicitly sorting by time (@option{--sort=time} or @option{-t})
+or when not using a long listing format,
+sort according to the status change time.
+
+@item -f
+@opindex -f
+@cindex unsorted directory listing
+@cindex directory order, listing by
+Primarily, like @option{-U}---do not sort; list the files in whatever
+order they are stored in the directory. But also enable @option{-a} (list
+all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
+were specified before the @option{-f}).
+
+@item -r
+@itemx --reverse
+@opindex -r
+@opindex --reverse
+@cindex reverse sorting
+Reverse whatever the sorting method is---e.g., list files in reverse
+alphabetical order, youngest first, smallest first, or whatever.
+
+@item -S
+@itemx --sort=size
+@opindex -S
+@opindex --sort
+@opindex size of files@r{, sorting files by}
+Sort by file size, largest first.
+
+@item -t
+@itemx --sort=time
+@opindex -t
+@opindex --sort
+@opindex modification time@r{, sorting files by}
+Sort by modification time (the @samp{mtime} in the inode), newest first.
+
+@item -u
+@itemx --time=atime
+@itemx --time=access
+@itemx --time=use
+@opindex -u
+@opindex --time
+@opindex use time@r{, printing or sorting files by}
+@opindex atime@r{, printing or sorting files by}
+@opindex access time@r{, printing or sorting files by}
+If the long listing format (e.g., @option{--format=long}) is being used,
+print the last access time (the @samp{atime} in the inode).
+When explicitly sorting by time (@option{--sort=time} or @option{-t})
+or when not using a long listing format, sort according to the access time.
+
+@item -U
+@itemx --sort=none
+@opindex -U
+@opindex --sort
+@opindex none@r{, sorting option for @command{ls}}
+Do not sort; list the files in whatever order they are
+stored in the directory. (Do not do any of the other unrelated things
+that @option{-f} does.) This is especially useful when listing very large
+directories, since not doing any sorting can be noticeably faster.
+
+@item -v
+@itemx --sort=version
+@opindex -v
+@opindex --sort
+@opindex version@r{, sorting option for @command{ls}}
+Sort by version name and number, lowest first. It behaves like a default
+sort, except that each sequence of decimal digits is treated numerically
+as an index/version number. (@xref{More details about version sort}.)
+
+@item -X
+@itemx --sort=extension
+@opindex -X
+@opindex --sort
+@opindex extension@r{, sorting files by}
+Sort directory contents alphabetically by file extension (characters
+after the last @samp{.}); files with no extension are sorted first.
+
+@end table
+
+
+@node More details about version sort
+@subsection More details about version sort
+
+The version sort takes into account the fact that file names frequently include
+indices or version numbers. Standard sorting functions usually do not produce
+the ordering that people expect because comparisons are made on a
+character-by-character basis. The version
+sort addresses this problem, and is especially useful when browsing
+directories that contain many files with indices/version numbers in their
+names:
+
+@example
+$ ls -1 $ ls -1v
+foo.zml-1.gz foo.zml-1.gz
+foo.zml-100.gz foo.zml-2.gz
+foo.zml-12.gz foo.zml-6.gz
+foo.zml-13.gz foo.zml-12.gz
+foo.zml-2.gz foo.zml-13.gz
+foo.zml-25.gz foo.zml-25.gz
+foo.zml-6.gz foo.zml-100.gz
+@end example
+
+Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
+are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
+the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
+@var{ver1} < @var{ver2} implies that the name composed of
+``@var{prefix} @var{ver1} @var{suffix}'' sorts before
+``@var{prefix} @var{ver2} @var{suffix}''.
+
+Note also that leading zeros of numeric parts are ignored:
+
+@example
+$ ls -1 $ ls -1v
+abc-1.007.tgz abc-1.01a.tgz
+abc-1.012b.tgz abc-1.007.tgz
+abc-1.01a.tgz abc-1.012b.tgz
+@end example
+
+This functionality is implemented using gnulib's @code{filevercmp} function.
+One result of that implementation decision is that @samp{ls -v}
+and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
+which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
+to @samp{C}.
+
+@node General output formatting
+@subsection General output formatting
+
+These options affect the appearance of the overall output.
+
+@table @samp
+
+@item -1
+@itemx --format=single-column
+@opindex -1
+@opindex --format
+@opindex single-column @r{output of files}
+List one file per line. This is the default for @command{ls} when standard
+output is not a terminal.
+
+@item -C
+@itemx --format=vertical
+@opindex -C
+@opindex --format
+@opindex vertical @r{sorted files in columns}
+List files in columns, sorted vertically. This is the default for
+@command{ls} if standard output is a terminal. It is always the default
+for the @command{dir} program.
+@sc{gnu} @command{ls} uses variable width columns to display as many files as
+possible in the fewest lines.
+
+@item --color [=@var{when}]
+@opindex --color
+@cindex color, distinguishing file types with
+Specify whether to use color for distinguishing file types. @var{when}
+may be omitted, or one of:
+@itemize @bullet
+@item none
+@vindex none @r{color option}
+- Do not use color at all. This is the default.
+@item auto
+@vindex auto @r{color option}
+@cindex terminal, using color iff
+- Only use color if standard output is a terminal.
+@item always
+@vindex always @r{color option}
+- Always use color.
+@end itemize
+Specifying @option{--color} and no @var{when} is equivalent to
+@option{--color=always}.
+Piping a colorized listing through a pager like @command{more} or
+@command{less} usually produces unreadable results. However, using
+@code{more -f} does seem to work.
+
+@item -F
+@itemx --classify
+@itemx --indicator-style=classify
+@opindex -F
+@opindex --classify
+@opindex --indicator-style
+@cindex file type and executables, marking
+@cindex executables and file type, marking
+Append a character to each file name indicating the file type. Also,
+for regular files that are executable, append @samp{*}. The file type
+indicators are @samp{/} for directories, @samp{@@} for symbolic links,
+@samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
+and nothing for regular files.
+@c The following sentence is the same as the one for -d.
+Do not follow symbolic links listed on the
+command line unless the @option{--dereference-command-line} (@option{-H}),
+@option{--dereference} (@option{-L}), or
+@option{--dereference-command-line-symlink-to-dir} options are specified.
+
+@item --file-type
+@itemx --indicator-style=file-type
+@opindex --file-type
+@opindex --indicator-style
+@cindex file type, marking
+Append a character to each file name indicating the file type. This is
+like @option{-F}, except that executables are not marked.
+
+@item --indicator-style=@var{word}
+@opindex --indicator-style
+Append a character indicator with style @var{word} to entry names,
+as follows:
+
+@table @samp
+@item none
+Do not append any character indicator; this is the default.
+@item slash
+Append @samp{/} for directories. This is the same as the @option{-p}
+option.
+@item file-type
+Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
+for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
+the same as the @option{--file-type} option.
+@item classify
+Append @samp{*} for executable regular files, otherwise behave as for
+@samp{file-type}. This is the same as the @option{-F} or
+@option{--classify} option.
+@end table
+
+@item -k
+@opindex -k
+Print file sizes in 1024-byte blocks, overriding the default block
+size (@pxref{Block size}).
+This option is equivalent to @option{--block-size=1K}.
+
+@item -m
+@itemx --format=commas
+@opindex -m
+@opindex --format
+@opindex commas@r{, outputting between files}
+List files horizontally, with as many as will fit on each line,
+separated by @samp{, } (a comma and a space).
+
+@item -p
+@itemx --indicator-style=slash
+@opindex -p
+@opindex --indicator-style
+@cindex file type, marking
+Append a @samp{/} to directory names.
+
+@item -x
+@itemx --format=across
+@itemx --format=horizontal
+@opindex -x
+@opindex --format
+@opindex across@r{, listing files}
+@opindex horizontal@r{, listing files}
+List the files in columns, sorted horizontally.
+
+@item -T @var{cols}
+@itemx --tabsize=@var{cols}
+@opindex -T
+@opindex --tabsize
+Assume that each tab stop is @var{cols} columns wide. The default is 8.
+@command{ls} uses tabs where possible in the output, for efficiency. If
+@var{cols} is zero, do not use tabs at all.
+
+@c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
+Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
+do not properly align columns to the right of a TAB following a
+non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
+@option{-T0} option or put @code{TABSIZE=0} in your environment to tell
+@command{ls} to align using spaces, not tabs.
+
+@item -w
+@itemx --width=@var{cols}
+@opindex -w
+@opindex --width
+@vindex COLUMNS
+Assume the screen is @var{cols} columns wide. The default is taken
+from the terminal settings if possible; otherwise the environment
+variable @env{COLUMNS} is used if it is set; otherwise the default
+is 80.
+
+@end table
+
+
+@node Formatting file timestamps
+@subsection Formatting file timestamps
+
+By default, file timestamps are listed in abbreviated form. Most
+locales use a timestamp like @samp{2002-03-30 23:45}. However, the
+default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
+for non-recent timestamps, and a date-without-year and time like
+@samp{Mar 30 23:45} for recent timestamps.
+
+A timestamp is considered to be @dfn{recent} if it is less than six
+months old, and is not dated in the future. If a timestamp dated
+today is not listed in recent form, the timestamp is in the future,
+which means you probably have clock skew problems which may break
+programs like @command{make} that rely on file timestamps.
+
+@vindex TZ
+Time stamps are listed according to the time zone rules specified by
+the @env{TZ} environment variable, or by the system default rules if
+@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
+with @env{TZ}, libc, The GNU C Library Reference Manual}.
+
+The following option changes how file timestamps are printed.
+
+@table @samp
+@item --time-style=@var{style}
+@opindex --time-style
+@cindex time style
+List timestamps in style @var{style}. The @var{style} should
+be one of the following:
+
+@table @samp
+@item +@var{format}
+@vindex LC_TIME
+List timestamps using @var{format}, where @var{format} is interpreted
+like the format argument of @command{date} (@pxref{date invocation}).
+For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
+@command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
+with @command{date}, @var{format}'s interpretation is affected by the
+@env{LC_TIME} locale category.
+
+If @var{format} contains two format strings separated by a newline,
+the former is used for non-recent files and the latter for recent
+files; if you want output columns to line up, you may need to insert
+spaces in one of the two formats.
+
+@item full-iso
+List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
+format with nanosecond precision, e.g., @samp{2002-03-30
+23:45:56.477817180 -0700}. This style is equivalent to
+@samp{+%Y-%m-%d %H:%M:%S.%N %z}.
+
+This is useful because the time output includes all the information that
+is available from the operating system. For example, this can help
+explain @command{make}'s behavior, since @acronym{GNU} @command{make}
+uses the full timestamp to determine whether a file is out of date.
+
+@item long-iso
+List @acronym{ISO} 8601 date and time in minutes, e.g.,
+@samp{2002-03-30 23:45}. These timestamps are shorter than
+@samp{full-iso} timestamps, and are usually good enough for everyday
+work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
+
+@item iso
+List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
+@samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
+minute for recent timestamps (e.g., @samp{03-30 23:45}). These
+timestamps are uglier than @samp{long-iso} timestamps, but they carry
+nearly the same information in a smaller space and their brevity helps
+@command{ls} output fit within traditional 80-column output lines.
+The following two @command{ls} invocations are equivalent:
+
+@example
+newline='
+'
+ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
+ls -l --time-style="iso"
+@end example
+
+@item locale
+@vindex LC_TIME
+List timestamps in a locale-dependent form. For example, a Finnish
+locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
+and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
+timestamps typically consume more space than @samp{iso} timestamps and
+are harder for programs to parse because locale conventions vary so
+widely, but they are easier for many people to read.
+
+The @env{LC_TIME} locale category specifies the timestamp format. The
+default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
+@ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
+@command{ls} invocations are equivalent:
+
+@example
+newline='
+'
+ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
+ls -l --time-style="locale"
+@end example
+
+Other locales behave differently. For example, in a German locale,
+@option{--time-style="locale"} might be equivalent to
+@option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
+and might generate timestamps like @samp{30. M@"ar 2002@ } and
+@samp{30. M@"ar 23:45}.
+
+@item posix-@var{style}
+@vindex LC_TIME
+List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
+category is @acronym{POSIX}, @var{style} timestamps otherwise. For
+example, the @samp{posix-long-iso} style lists
+timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
+the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
+@end table
+@end table
+
+@vindex TIME_STYLE
+You can specify the default value of the @option{--time-style} option
+with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
+the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
+later use the @option{--dired} option and therefore can parse any date
+format, but if you are using Emacs 21.1 or 21.2 and specify a
+non-@acronym{POSIX} locale you may need to set
+@samp{TIME_STYLE="posix-long-iso"}.
+
+To avoid certain denial-of-service attacks, timestamps that would be
+longer than 1000 bytes may be treated as errors.
+
+
+@node Formatting the file names
+@subsection Formatting the file names
+
+These options change how file names themselves are printed.
+
+@table @samp
+
+@item -b
+@itemx --escape
+@itemx --quoting-style=escape
+@opindex -b
+@opindex --escape
+@opindex --quoting-style
+@cindex backslash sequences for file names
+Quote nongraphic characters in file names using alphabetic and octal
+backslash sequences like those used in C.
+
+@item -N
+@itemx --literal
+@itemx --quoting-style=literal
+@opindex -N
+@opindex --literal
+@opindex --quoting-style
+Do not quote file names. However, with @command{ls} nongraphic
+characters are still printed as question marks if the output is a
+terminal and you do not specify the @option{--show-control-chars}
+option.
+
+@item -q
+@itemx --hide-control-chars
+@opindex -q
+@opindex --hide-control-chars
+Print question marks instead of nongraphic characters in file names.
+This is the default if the output is a terminal and the program is
+@command{ls}.
+
+@item -Q
+@itemx --quote-name
+@itemx --quoting-style=c
+@opindex -Q
+@opindex --quote-name
+@opindex --quoting-style
+Enclose file names in double quotes and quote nongraphic characters as
+in C.
+
+@item --quoting-style=@var{word}
+@opindex --quoting-style
+@cindex quoting style
+Use style @var{word} to quote file names and other strings that may
+contain arbitrary characters. The @var{word} should
+be one of the following:
+
+@table @samp
+@item literal
+Output strings as-is; this is the same as the @option{-N} or
+@option{--literal} option.
+@item shell
+Quote strings for the shell if they contain shell metacharacters or would
+cause ambiguous output.
+The quoting is suitable for @acronym{POSIX}-compatible shells like
+@command{bash}, but it does not always work for incompatible shells
+like @command{csh}.
+@item shell-always
+Quote strings for the shell, even if they would normally not require quoting.
+@item c
+Quote strings as for C character string literals, including the
+surrounding double-quote characters; this is the same as the
+@option{-Q} or @option{--quote-name} option.
+@item escape
+Quote strings as for C character string literals, except omit the
+surrounding double-quote
+characters; this is the same as the @option{-b} or @option{--escape} option.
+@item clocale
+Quote strings as for C character string literals, except use
+surrounding quotation marks appropriate for the
+locale.
+@item locale
+@c Use @t instead of @samp to avoid duplicate quoting in some output styles.
+Quote strings as for C character string literals, except use
+surrounding quotation marks appropriate for the locale, and quote
+@t{`like this'} instead of @t{"like
+this"} in the default C locale. This looks nicer on many displays.
+@end table
+
+You can specify the default value of the @option{--quoting-style} option
+with the environment variable @env{QUOTING_STYLE}. If that environment
+variable is not set, the default value is @samp{literal}, but this
+default may change to @samp{shell} in a future version of this package.
+
+@item --show-control-chars
+@opindex --show-control-chars
+Print nongraphic characters as-is in file names.
+This is the default unless the output is a terminal and the program is
+@command{ls}.
+
+@end table
+
+
+@node dir invocation
+@section @command{dir}: Briefly list directory contents
+
+@pindex dir
+@cindex directory listing, brief
+
+@command{dir} is equivalent to @code{ls -C
+-b}; that is, by default files are listed in columns, sorted vertically,
+and special characters are represented by backslash escape sequences.
+
+@xref{ls invocation, @command{ls}}.
+
+
+@node vdir invocation
+@section @command{vdir}: Verbosely list directory contents
+
+@pindex vdir
+@cindex directory listing, verbose
+
+@command{vdir} is equivalent to @code{ls -l
+-b}; that is, by default files are listed in long format and special
+characters are represented by backslash escape sequences.
+
+@node dircolors invocation
+@section @command{dircolors}: Color setup for @command{ls}
+
+@pindex dircolors
+@cindex color setup
+@cindex setup for color
+
+@command{dircolors} outputs a sequence of shell commands to set up the
+terminal for color output from @command{ls} (and @command{dir}, etc.).
+Typical usage:
+
+@example
+eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
+@end example
+
+If @var{file} is specified, @command{dircolors} reads it to determine which
+colors to use for which file types and extensions. Otherwise, a
+precompiled database is used. For details on the format of these files,
+run @samp{dircolors --print-database}.
+
+To make @command{dircolors} read a @file{~/.dircolors} file if it
+exists, you can put the following lines in your @file{~/.bashrc} (or
+adapt them to your favorite shell):
+
+@example
+d=.dircolors
+test -r $d && eval "$(dircolors $d)"
+@end example
+
+@vindex LS_COLORS
+@vindex SHELL @r{environment variable, and color}
+The output is a shell command to set the @env{LS_COLORS} environment
+variable. You can specify the shell syntax to use on the command line,
+or @command{dircolors} will guess it from the value of the @env{SHELL}
+environment variable.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -b
+@itemx --sh
+@itemx --bourne-shell
+@opindex -b
+@opindex --sh
+@opindex --bourne-shell
+@cindex Bourne shell syntax for color setup
+@cindex @command{sh} syntax for color setup
+Output Bourne shell commands. This is the default if the @env{SHELL}
+environment variable is set and does not end with @samp{csh} or
+@samp{tcsh}.
+
+@item -c
+@itemx --csh
+@itemx --c-shell
+@opindex -c
+@opindex --csh
+@opindex --c-shell
+@cindex C shell syntax for color setup
+@cindex @command{csh} syntax for color setup
+Output C shell commands. This is the default if @code{SHELL} ends with
+@command{csh} or @command{tcsh}.
+
+@item -p
+@itemx --print-database
+@opindex -p
+@opindex --print-database
+@cindex color database, printing
+@cindex database for color setup, printing
+@cindex printing color database
+Print the (compiled-in) default color configuration database. This
+output is itself a valid configuration file, and is fairly descriptive
+of the possibilities.
+
+@end table
+
+@exitstatus
+
+
+@node Basic operations
+@chapter Basic operations
+
+@cindex manipulating files
+
+This chapter describes the commands for basic file manipulation:
+copying, moving (renaming), and deleting (removing).
+
+@menu
+* cp invocation:: Copy files.
+* dd invocation:: Convert and copy a file.
+* install invocation:: Copy files and set attributes.
+* mv invocation:: Move (rename) files.
+* rm invocation:: Remove files or directories.
+* shred invocation:: Remove files more securely.
+@end menu
+
+
+@node cp invocation
+@section @command{cp}: Copy files and directories
+
+@pindex cp
+@cindex copying files and directories
+@cindex files, copying
+@cindex directories, copying
+
+@command{cp} copies files (or, optionally, directories). The copy is
+completely independent of the original. You can either copy one file to
+another, or copy arbitrarily many files to a destination directory.
+Synopses:
+
+@example
+cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
+cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
+@end example
+
+@itemize @bullet
+@item
+If two file names are given, @command{cp} copies the first file to the
+second.
+
+@item
+If the @option{--target-directory} (@option{-t}) option is given, or
+failing that if the last file is a directory and the
+@option{--no-target-directory} (@option{-T}) option is not given,
+@command{cp} copies each @var{source} file to the specified directory,
+using the @var{source}s' names.
+@end itemize
+
+Generally, files are written just as they are read. For exceptions,
+see the @option{--sparse} option below.
+
+By default, @command{cp} does not copy directories. However, the
+@option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
+copy recursively by descending into source directories and copying files
+to corresponding destination directories.
+
+When copying from a symbolic link, @command{cp} normally follows the
+link only when not copying
+recursively. This default can be overridden with the
+@option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
+(@option{-L}), @option{--no-dereference} (@option{-P}), and
+@option{-H} options. If more than one of these options is specified,
+the last one silently overrides the others.
+
+When copying to a symbolic link, @command{cp} follows the
+link only when it refers to an existing regular file.
+However, when copying to a dangling symbolic link, @command{cp}
+refuses by default, and fails with a diagnostic, since the operation
+is inherently dangerous. This behavior is contrary to historical
+practice and to @acronym{POSIX}.
+Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
+the target of a dangling destination symlink, in spite of the possible risk.
+Also, when an option like
+@option{--backup} or @option{--link} acts to rename or remove the
+destination before copying, @command{cp} renames or removes the
+symbolic link rather than the file it points to.
+
+By default, @command{cp} copies the contents of special files only
+when not copying recursively. This default can be overridden with the
+@option{--copy-contents} option.
+
+@cindex self-backups
+@cindex backups, making only
+@command{cp} generally refuses to copy a file onto itself, with the
+following exception: if @option{--force --backup} is specified with
+@var{source} and @var{dest} identical, and referring to a regular file,
+@command{cp} will make a backup file, either regular or numbered, as
+specified in the usual ways (@pxref{Backup options}). This is useful when
+you simply want to make a backup of an existing file before changing it.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --archive
+@opindex -a
+@opindex --archive
+Preserve as much as possible of the structure and attributes of the
+original files in the copy (but do not attempt to preserve internal
+directory structure; i.e., @samp{ls -U} may list the entries in a copied
+directory in a different order).
+Try to preserve SELinux security context and extended attributes (xattr),
+but ignore any failure to do that and print no corresponding diagnostic.
+Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
+
+@item -b
+@itemx @w{@kbd{--backup}[=@var{method}]}
+@opindex -b
+@opindex --backup
+@vindex VERSION_CONTROL
+@cindex backups, making
+@xref{Backup options}.
+Make a backup of each file that would otherwise be overwritten or removed.
+As a special case, @command{cp} makes a backup of @var{source} when the force
+and backup options are given and @var{source} and @var{dest} are the same
+name for an existing, regular file. One useful application of this
+combination of options is this tiny Bourne shell script:
+
+@example
+#!/bin/sh
+# Usage: backup FILE...
+# Create a @sc{gnu}-style backup of each listed FILE.
+for i; do
+ cp --backup --force -- "$i" "$i"
+done
+@end example
+
+@item --copy-contents
+@cindex directories, copying recursively
+@cindex copying directories recursively
+@cindex recursively copying directories
+@cindex non-directories, copying as special files
+If copying recursively, copy the contents of any special files (e.g.,
+FIFOs and device files) as if they were regular files. This means
+trying to read the data in each source file and writing it to the
+destination. It is usually a mistake to use this option, as it
+normally has undesirable effects on special files like FIFOs and the
+ones typically found in the @file{/dev} directory. In most cases,
+@code{cp -R --copy-contents} will hang indefinitely trying to read
+from FIFOs and special files like @file{/dev/console}, and it will
+fill up your destination disk if you use it to copy @file{/dev/zero}.
+This option has no effect unless copying recursively, and it does not
+affect the copying of symbolic links.
+
+@item -d
+@opindex -d
+@cindex symbolic links, copying
+@cindex hard links, preserving
+Copy symbolic links as symbolic links rather than copying the files that
+they point to, and preserve hard links between source files in the copies.
+Equivalent to @option{--no-dereference --preserve=links}.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+When copying without this option and an existing destination file cannot
+be opened for writing, the copy fails. However, with @option{--force}),
+when a destination file cannot be opened, @command{cp} then removes it and
+tries to open it again. Contrast this behavior with that enabled by
+@option{--link} and @option{--symbolic-link}, whereby the destination file
+is never opened but rather is removed unconditionally. Also see the
+description of @option{--remove-destination}.
+
+This option is independent of the @option{--interactive} or
+@option{-i} option: neither cancels the effect of the other.
+
+This option is redundant if the @option{--no-clobber} or @option{-n} option is
+used.
+
+@item -H
+@opindex -H
+If a command line argument specifies a symbolic link, then copy the
+file it points to rather than the symbolic link itself. However,
+copy (preserving its nature) any symbolic link that is encountered
+via recursive traversal.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+When copying a file other than a directory, prompt whether to
+overwrite an existing destination file. The @option{-i} option overrides
+a previous @option{-n} option.
+
+@item -l
+@itemx --link
+@opindex -l
+@opindex --link
+Make hard links instead of copies of non-directories.
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+Follow symbolic links when copying from them.
+
+@item -n
+@itemx --no-clobber
+@opindex -n
+@opindex --no-clobber
+Do not overwrite an existing file. The @option{-n} option overrides a previous
+@option{-i} option. This option is mutually exclusive with @option{-b} or
+@option{--backup} option.
+
+@item -P
+@itemx --no-dereference
+@opindex -P
+@opindex --no-dereference
+@cindex symbolic links, copying
+Copy symbolic links as symbolic links rather than copying the files that
+they point to. This option affects only symbolic links in the source;
+symbolic links in the destination are always followed if possible.
+
+@item -p
+@itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
+@opindex -p
+@opindex --preserve
+@cindex file information, preserving, extended attributes, xattr
+Preserve the specified attributes of the original files.
+If specified, the @var{attribute_list} must be a comma-separated list
+of one or more of the following strings:
+
+@table @samp
+@itemx mode
+Preserve the file mode bits and access control lists.
+@itemx ownership
+Preserve the owner and group. On most modern systems,
+only users with appropriate privileges may change the owner of a file,
+and ordinary users
+may preserve the group ownership of a file only if they happen to be
+a member of the desired group.
+@itemx timestamps
+Preserve the times of last access and last modification, when possible.
+In general, it is not possible to preserve these attributes
+when the affected file is a symbolic link.
+However, FreeBSD now provides the @code{lutimes} function, which makes
+it possible even for symbolic links. However, this implementation does
+not yet take advantage of that.
+@c FIXME: once we provide lutimes support, update the above.
+@itemx links
+Preserve in the destination files
+any links between corresponding source files.
+@c Give examples illustrating how hard links are preserved.
+@c Also, show how soft links map to hard links with -L and -H.
+@itemx context
+Preserve SELinux security context of the file. @command{cp} will fail
+if the preserving of SELinux security context is not succesful.
+@itemx xattr
+Preserve extended attributes if @command{cp} is built with xattr support,
+and xattrs are supported and enabled on your file system.
+If SELinux context and/or ACLs are implemented using xattrs,
+they are preserved by this option as well.
+@itemx all
+Preserve all file attributes.
+Equivalent to specifying all of the above, but with the difference
+that failure to preserve SELinux security context or extended attributes
+does not change @command{cp}'s exit status.
+@command{cp} does diagnose such failures.
+@end table
+
+Using @option{--preserve} with no @var{attribute_list} is equivalent
+to @option{--preserve=mode,ownership,timestamps}.
+
+In the absence of this option, each destination file is created with the
+mode bits of the corresponding source file, minus the bits set in the
+umask and minus the set-user-ID and set-group-ID bits.
+@xref{File permissions}.
+
+@itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
+@cindex file information, preserving
+Do not preserve the specified attributes. The @var{attribute_list}
+has the same form as for @option{--preserve}.
+
+@itemx --parents
+@opindex --parents
+@cindex parent directories and @command{cp}
+Form the name of each destination file by appending to the target
+directory a slash and the specified name of the source file. The last
+argument given to @command{cp} must be the name of an existing directory.
+For example, the command:
+
+@example
+cp --parents a/b/c existing_dir
+@end example
+
+@noindent
+copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
+any missing intermediate directories.
+
+@item -R
+@itemx -r
+@itemx --recursive
+@opindex -R
+@opindex -r
+@opindex --recursive
+@cindex directories, copying recursively
+@cindex copying directories recursively
+@cindex recursively copying directories
+@cindex non-directories, copying as special files
+Copy directories recursively. By default, do not follow symbolic
+links in the source; see the @option{--archive} (@option{-a}), @option{-d},
+@option{--dereference} (@option{-L}), @option{--no-dereference}
+(@option{-P}), and @option{-H} options. Special files are copied by
+creating a destination file of the same type as the source; see the
+@option{--copy-contents} option. It is not portable to use
+@option{-r} to copy symbolic links or special files. On some
+non-@sc{gnu} systems, @option{-r} implies the equivalent of
+@option{-L} and @option{--copy-contents} for historical reasons.
+Also, it is not portable to use @option{-R} to copy symbolic links
+unless you also specify @option{-P}, as @acronym{POSIX} allows
+implementations that dereference symbolic links by default.
+
+@item --remove-destination
+@opindex --remove-destination
+Remove each existing destination file before attempting to open it
+(contrast with @option{-f} above).
+
+@item --sparse=@var{when}
+@opindex --sparse=@var{when}
+@cindex sparse files, copying
+@cindex holes, copying files with
+@findex read @r{system call, and holes}
+A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
+does not occupy any physical disk blocks; the @samp{read} system call
+reads these as zeros. This can both save considerable disk space and
+increase speed, since many binary files contain lots of consecutive zero
+bytes. By default, @command{cp} detects holes in input source files via a crude
+heuristic and makes the corresponding output file sparse as well.
+Only regular files may be sparse.
+
+The @var{when} value can be one of the following:
+
+@table @samp
+@item auto
+The default behavior: if the input file is sparse, attempt to make
+the output file sparse, too. However, if an output file exists but
+refers to a non-regular file, then do not attempt to make it sparse.
+
+@item always
+For each sufficiently long sequence of zero bytes in the input file,
+attempt to create a corresponding hole in the output file, even if the
+input file does not appear to be sparse.
+This is useful when the input file resides on a file system
+that does not support sparse files
+(for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
+but the output file is on a type of file system that does support them.
+Holes may be created only in regular files, so if the destination file
+is of some other type, @command{cp} does not even try to make it sparse.
+
+@item never
+Never make the output file sparse.
+This is useful in creating a file for use with the @command{mkswap} command,
+since such a file must not have any holes.
+@end table
+
+@optStripTrailingSlashes
+
+@item -s
+@itemx --symbolic-link
+@opindex -s
+@opindex --symbolic-link
+@cindex symbolic links, copying with
+Make symbolic links instead of copies of non-directories. All source
+file names must be absolute (starting with @samp{/}) unless the
+destination files are in the current directory. This option merely
+results in an error message on systems that do not support symbolic links.
+
+@optBackupSuffix
+
+@optTargetDirectory
+
+@optNoTargetDirectory
+
+@item -u
+@itemx --update
+@opindex -u
+@opindex --update
+@cindex newer files, copying only
+Do not copy a non-directory that has an existing destination with the
+same or newer modification time. If time stamps are being preserved,
+the comparison is to the source time stamp truncated to the
+resolutions of the destination file system and of the system calls
+used to update time stamps; this avoids duplicate work if several
+@samp{cp -pu} commands are executed with the same source and
+destination.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before copying it.
+
+@item -x
+@itemx --one-file-system
+@opindex -x
+@opindex --one-file-system
+@cindex file systems, omitting copying to different
+Skip subdirectories that are on different file systems from the one that
+the copy started on.
+However, mount point directories @emph{are} copied.
+
+@end table
+
+@exitstatus
+
+
+@node dd invocation
+@section @command{dd}: Convert and copy a file
+
+@pindex dd
+@cindex converting while copying a file
+
+@command{dd} copies a file (from standard input to standard output, by
+default) with a changeable I/O block size, while optionally performing
+conversions on it. Synopses:
+
+@example
+dd [@var{operand}]@dots{}
+dd @var{option}
+@end example
+
+The only options are @option{--help} and @option{--version}.
+@xref{Common options}. @command{dd} accepts the following operands.
+
+@table @samp
+
+@item if=@var{file}
+@opindex if
+Read from @var{file} instead of standard input.
+
+@item of=@var{file}
+@opindex of
+Write to @var{file} instead of standard output. Unless
+@samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
+bytes (or the size specified with @samp{seek=}).
+
+@item ibs=@var{bytes}
+@opindex ibs
+@cindex block size of input
+@cindex input block size
+Set the input block size to @var{bytes}.
+This makes @command{dd} read @var{bytes} per block.
+The default is 512 bytes.
+
+@item obs=@var{bytes}
+@opindex obs
+@cindex block size of output
+@cindex output block size
+Set the output block size to @var{bytes}.
+This makes @command{dd} write @var{bytes} per block.
+The default is 512 bytes.
+
+@item bs=@var{bytes}
+@opindex bs
+@cindex block size
+Set both input and output block sizes to @var{bytes}.
+This makes @command{dd} read and write @var{bytes} per block,
+overriding any @samp{ibs} and @samp{obs} settings.
+In addition, if no data-transforming @option{conv} option is specified,
+each input block is copied to the output as a single block,
+without aggregating short reads.
+
+@item cbs=@var{bytes}
+@opindex cbs
+@cindex block size of conversion
+@cindex conversion block size
+@cindex fixed-length records, converting to variable-length
+@cindex variable-length records, converting to fixed-length
+Set the conversion block size to @var{bytes}.
+When converting variable-length records to fixed-length ones
+(@option{conv=block}) or the reverse (@option{conv=unblock}),
+use @var{bytes} as the fixed record length.
+
+@item skip=@var{blocks}
+@opindex skip
+Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
+
+@item seek=@var{blocks}
+@opindex seek
+Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
+
+@item count=@var{blocks}
+@opindex count
+Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
+of everything until the end of the file.
+
+@item status=noxfer
+@opindex status
+Do not print the overall transfer rate and volume statistics
+that normally make up the third status line when @command{dd} exits.
+
+@item conv=@var{conversion}[,@var{conversion}]@dots{}
+@opindex conv
+Convert the file as specified by the @var{conversion} argument(s).
+(No spaces around any comma(s).)
+
+Conversions:
+
+@table @samp
+
+@item ascii
+@opindex ascii@r{, converting to}
+Convert @acronym{EBCDIC} to @acronym{ASCII},
+using the conversion table specified by @acronym{POSIX}.
+This provides a 1:1 translation for all 256 bytes.
+
+@item ebcdic
+@opindex ebcdic@r{, converting to}
+Convert @acronym{ASCII} to @acronym{EBCDIC}.
+This is the inverse of the @samp{ascii} conversion.
+
+@item ibm
+@opindex alternate ebcdic@r{, converting to}
+Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
+using the alternate conversion table specified by @acronym{POSIX}.
+This is not a 1:1 translation, but reflects common historical practice
+for @samp{~}, @samp{[}, and @samp{]}.
+
+The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
+mutually exclusive.
+
+@item block
+@opindex block @r{(space-padding)}
+For each line in the input, output @samp{cbs} bytes, replacing the
+input newline with a space and padding with spaces as necessary.
+
+@item unblock
+@opindex unblock
+Replace trailing spaces in each @samp{cbs}-sized input block with a
+newline.
+
+The @samp{block} and @samp{unblock} conversions are mutually exclusive.
+
+@item lcase
+@opindex lcase@r{, converting to}
+Change uppercase letters to lowercase.
+
+@item ucase
+@opindex ucase@r{, converting to}
+Change lowercase letters to uppercase.
+
+The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
+
+@item swab
+@opindex swab @r{(byte-swapping)}
+@cindex byte-swapping
+Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
+when an odd number of bytes are read---the last byte is simply copied
+(since there is nothing to swap it with).
+
+@item noerror
+@opindex noerror
+@cindex read errors, ignoring
+Continue after read errors.
+
+@item nocreat
+@opindex nocreat
+@cindex creating output file, avoiding
+Do not create the output file; the output file must already exist.
+
+@item excl
+@opindex excl
+@cindex creating output file, requiring
+Fail if the output file already exists; @command{dd} must create the
+output file itself.
+
+The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
+
+@item notrunc
+@opindex notrunc
+@cindex truncating output file, avoiding
+Do not truncate the output file.
+
+@item sync
+@opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
+Pad every input block to size of @samp{ibs} with trailing zero bytes.
+When used with @samp{block} or @samp{unblock}, pad with spaces instead of
+zero bytes.
+
+@item fdatasync
+@opindex fdatasync
+@cindex synchronized data writes, before finishing
+Synchronize output data just before finishing. This forces a physical
+write of output data.
+
+@item fsync
+@opindex fsync
+@cindex synchronized data and metadata writes, before finishing
+Synchronize output data and metadata just before finishing. This
+forces a physical write of output data and metadata.
+
+@end table
+
+@item iflag=@var{flag}[,@var{flag}]@dots{}
+@opindex iflag
+Access the input file using the flags specified by the @var{flag}
+argument(s). (No spaces around any comma(s).)
+
+@item oflag=@var{flag}[,@var{flag}]@dots{}
+@opindex oflag
+Access the output file using the flags specified by the @var{flag}
+argument(s). (No spaces around any comma(s).)
+
+Here are the flags. Not every flag is supported on every operating
+system.
+
+@table @samp
+
+@item append
+@opindex append
+@cindex appending to the output file
+Write in append mode, so that even if some other process is writing to
+this file, every @command{dd} write will append to the current
+contents of the file. This flag makes sense only for output.
+If you combine this flag with the @samp{of=@var{file}} operand,
+you should also specify @samp{conv=notrunc} unless you want the
+output file to be truncated before being appended to.
+
+@item cio
+@opindex cio
+@cindex concurrent I/O
+Use concurrent I/O mode for data. This mode performs direct I/O
+and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
+A file cannot be opened in CIO mode and with a standard open at the
+same time.
+
+@item direct
+@opindex direct
+@cindex direct I/O
+Use direct I/O for data, avoiding the buffer cache.
+
+@item directory
+@opindex directory
+@cindex directory I/O
+
+Fail unless the file is a directory. Most operating systems do not
+allow I/O to a directory, so this flag has limited utility.
+
+@item dsync
+@opindex dsync
+@cindex synchronized data reads
+Use synchronized I/O for data. For the output file, this forces a
+physical write of output data on each write. For the input file,
+this flag can matter when reading from a remote file that has been
+written to synchronously by some other process. Metadata (e.g.,
+last-access and last-modified time) is not necessarily synchronized.
+
+@item sync
+@opindex sync
+@cindex synchronized data and metadata I/O
+Use synchronized I/O for both data and metadata.
+
+@item nonblock
+@opindex nonblock
+@cindex nonblocking I/O
+Use non-blocking I/O.
+
+@item noatime
+@opindex noatime
+@cindex access time
+Do not update the file's access time.
+Some older file systems silently ignore this flag, so it is a good
+idea to test it on your files before relying on it.
+
+@item noctty
+@opindex noctty
+@cindex controlling terminal
+Do not assign the file to be a controlling terminal for @command{dd}.
+This has no effect when the file is not a terminal.
+On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
+at all.
+
+@item nofollow
+@opindex nofollow
+@cindex symbolic links, following
+Do not follow symbolic links.
+
+@item nolinks
+@opindex nolinks
+@cindex hard links
+Fail if the file has multiple hard links.
+
+@item binary
+@opindex binary
+@cindex binary I/O
+Use binary I/O. This option has an effect only on nonstandard
+platforms that distinguish binary from text I/O.
+
+@item text
+@opindex text
+@cindex text I/O
+Use text I/O. Like @samp{binary}, this option has no effect on
+standard platforms.
+
+@item fullblock
+@opindex fullblock
+Accumulate full blocks from input. The @code{read} system call
+may return early if a full block is not available.
+When that happens, continue calling @code{read} to fill the remainder
+of the block.
+This flag can be used only with @code{iflag}.
+
+@end table
+
+These flags are not supported on all systems, and @samp{dd} rejects
+attempts to use them when they are not supported. When reading from
+standard input or writing to standard output, the @samp{nofollow} and
+@samp{noctty} flags should not be specified, and the other flags
+(e.g., @samp{nonblock}) can affect how other processes behave with the
+affected file descriptors, even after @command{dd} exits.
+
+@end table
+
+@cindex multipliers after numbers
+The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
+followed by a multiplier: @samp{b}=512, @samp{c}=1,
+@samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
+standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
+
+Use different @command{dd} invocations to use different block sizes for
+skipping and I/O@. For example, the following shell commands copy data
+in 512 KiB blocks between a disk and a tape, but do not save or restore a
+4 KiB label at the start of the disk:
+
+@example
+disk=/dev/rdsk/c0t1d0s2
+tape=/dev/rmt/0
+
+# Copy all but the label from disk to tape.
+(dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
+
+# Copy from tape back to disk, but leave the disk label alone.
+(dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
+@end example
+
+Sending an @samp{INFO} signal to a running @command{dd}
+process makes it print I/O statistics to standard error
+and then resume copying. In the example below,
+@command{dd} is run in the background to copy 10 million blocks.
+The @command{kill} command makes it output intermediate I/O statistics,
+and when @command{dd} completes normally or is killed by the
+@code{SIGINT} signal, it outputs the final statistics.
+
+@example
+$ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
+$ kill -s INFO $pid; wait $pid
+3385223+0 records in
+3385223+0 records out
+1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
+10000000+0 records in
+10000000+0 records out
+5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
+@end example
+
+@vindex POSIXLY_CORRECT
+On systems lacking the @samp{INFO} signal @command{dd} responds to the
+@samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
+environment variable is set.
+
+@exitstatus
+
+
+@node install invocation
+@section @command{install}: Copy files and set attributes
+
+@pindex install
+@cindex copying files and setting attributes
+
+@command{install} copies files while setting their file mode bits and, if
+possible, their owner and group. Synopses:
+
+@example
+install [@var{option}]@dots{} [-T] @var{source} @var{dest}
+install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
+install [@var{option}]@dots{} -d @var{directory}@dots{}
+@end example
+
+@itemize @bullet
+@item
+If two file names are given, @command{install} copies the first file to the
+second.
+
+@item
+If the @option{--target-directory} (@option{-t}) option is given, or
+failing that if the last file is a directory and the
+@option{--no-target-directory} (@option{-T}) option is not given,
+@command{install} copies each @var{source} file to the specified
+directory, using the @var{source}s' names.
+
+@item
+If the @option{--directory} (@option{-d}) option is given,
+@command{install} creates each @var{directory} and any missing parent
+directories. Parent directories are created with mode
+@samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
+current umask. @xref{Directory Setuid and Setgid}, for how the
+set-user-ID and set-group-ID bits of parent directories are inherited.
+@end itemize
+
+@cindex Makefiles, installing programs in
+@command{install} is similar to @command{cp}, but allows you to control the
+attributes of destination files. It is typically used in Makefiles to
+copy programs into their destination directories. It refuses to copy
+files onto themselves.
+
+@cindex extended attributes, xattr
+@command{install} never preserves extended attributes (xattr).
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@optBackup
+
+@item -c
+@opindex -c
+Ignored; for compatibility with old Unix versions of @command{install}.
+
+@item -D
+@opindex -D
+Create any missing parent directories of @var{dest},
+then copy @var{source} to @var{dest}.
+This option is ignored if a destination directory is specified
+via @option{--target-directory=DIR}.
+
+@item -d
+@itemx --directory
+@opindex -d
+@opindex --directory
+@cindex directories, creating with given attributes
+@cindex parent directories, creating missing
+@cindex leading directories, creating missing
+Create any missing parent directories, giving them the default
+attributes. Then create each given directory, setting their owner,
+group and mode as given on the command line or to the defaults.
+
+@item -g @var{group}
+@itemx --group=@var{group}
+@opindex -g
+@opindex --group
+@cindex group ownership of installed files, setting
+Set the group ownership of installed files or directories to
+@var{group}. The default is the process's current group. @var{group}
+may be either a group name or a numeric group ID.
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex permissions of installed files, setting
+Set the file mode bits for the installed file or directory to @var{mode},
+which can be either an octal number, or a symbolic mode as in
+@command{chmod}, with @samp{a=} (no access allowed to anyone) as the
+point of departure (@pxref{File permissions}).
+The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
+execute for the owner, read and execute for group and other, and with
+set-user-ID and set-group-ID disabled.
+This default is not quite the same as @samp{755}, since it disables
+instead of preserving set-user-ID and set-group-ID on directories.
+@xref{Directory Setuid and Setgid}.
+
+@item -o @var{owner}
+@itemx --owner=@var{owner}
+@opindex -o
+@opindex --owner
+@cindex ownership of installed files, setting
+@cindex appropriate privileges
+@vindex root @r{as default owner}
+If @command{install} has appropriate privileges (is run as root), set the
+ownership of installed files or directories to @var{owner}. The default
+is @code{root}. @var{owner} may be either a user name or a numeric user
+ID.
+
+@item -p
+@itemx --preserve-timestamps
+@opindex -p
+@opindex --preserve-timestamps
+@cindex timestamps of installed files, preserving
+Set the time of last access and the time of last modification of each
+installed file to match those of each corresponding original file.
+When a file is installed without this option, its last access and
+last modification times are both set to the time of installation.
+This option is useful if you want to use the last modification times
+of installed files to keep track of when they were last built as opposed
+to when they were last installed.
+
+@item -s
+@itemx --strip
+@opindex -s
+@opindex --strip
+@cindex symbol table information, stripping
+@cindex stripping symbol table information
+Strip the symbol tables from installed binary executables.
+
+@itemx --strip-program=@var{program}
+@opindex --strip-program
+@cindex symbol table information, stripping, program
+Program used to strip binaries.
+
+@optBackupSuffix
+
+@optTargetDirectory
+
+@optNoTargetDirectory
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before copying it.
+
+@end table
+
+@exitstatus
+
+
+@node mv invocation
+@section @command{mv}: Move (rename) files
+
+@pindex mv
+
+@command{mv} moves or renames files (or directories). Synopses:
+
+@example
+mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
+mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
+mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
+@end example
+
+@itemize @bullet
+@item
+If two file names are given, @command{mv} moves the first file to the
+second.
+
+@item
+If the @option{--target-directory} (@option{-t}) option is given, or
+failing that if the last file is a directory and the
+@option{--no-target-directory} (@option{-T}) option is not given,
+@command{mv} moves each @var{source} file to the specified
+directory, using the @var{source}s' names.
+@end itemize
+
+@command{mv} can move any type of file from one file system to another.
+Prior to version @code{4.0} of the fileutils,
+@command{mv} could move only regular files between file systems.
+For example, now @command{mv} can move an entire directory hierarchy
+including special device files from one partition to another. It first
+uses some of the same code that's used by @code{cp -a} to copy the
+requested directories and files, then (assuming the copy succeeded)
+it removes the originals. If the copy fails, then the part that was
+copied to the destination partition is removed. If you were to copy
+three directories from one partition to another and the copy of the first
+directory succeeded, but the second didn't, the first would be left on
+the destination partition and the second and third would be left on the
+original partition.
+
+@cindex extended attributes, xattr
+@command{mv} always tries to copy extended attributes (xattr).
+
+@cindex prompting, and @command{mv}
+If a destination file exists but is normally unwritable, standard input
+is a terminal, and the @option{-f} or @option{--force} option is not given,
+@command{mv} prompts the user for whether to replace the file. (You might
+own the file, or have write permission on its directory.) If the
+response is not affirmative, the file is skipped.
+
+@emph{Warning}: Avoid specifying a source name with a trailing slash,
+when it might be a symlink to a directory.
+Otherwise, @command{mv} may do something very surprising, since
+its behavior depends on the underlying rename system call.
+On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
+However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
+renames not the symlink but rather the directory referenced by the symlink.
+@xref{Trailing slashes}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@optBackup
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+@cindex prompts, omitting
+Do not prompt the user before removing a destination file.
+@macro mvOptsIfn
+If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
+options, only the final one takes effect.
+@end macro
+@mvOptsIfn
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+@cindex prompts, forcing
+Prompt whether to overwrite each existing destination file, regardless
+of its permissions.
+If the response is not affirmative, the file is skipped.
+@mvOptsIfn
+
+@item -n
+@itemx --no-clobber
+@opindex -n
+@opindex --no-clobber
+@cindex prompts, omitting
+Do not overwrite an existing file.
+@mvOptsIfn
+This option is mutually exclusive with @option{-b} or @option{--backup} option.
+
+@item -u
+@itemx --update
+@opindex -u
+@opindex --update
+@cindex newer files, moving only
+Do not move a non-directory that has an existing destination with the
+same or newer modification time.
+If the move is across file system boundaries, the comparison is to the
+source time stamp truncated to the resolutions of the destination file
+system and of the system calls used to update time stamps; this avoids
+duplicate work if several @samp{mv -u} commands are executed with the
+same source and destination.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before moving it.
+
+@optStripTrailingSlashes
+
+@optBackupSuffix
+
+@optTargetDirectory
+
+@optNoTargetDirectory
+
+@end table
+
+@exitstatus
+
+
+@node rm invocation
+@section @command{rm}: Remove files or directories
+
+@pindex rm
+@cindex removing files or directories
+
+@command{rm} removes each given @var{file}. By default, it does not remove
+directories. Synopsis:
+
+@example
+rm [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+@cindex prompting, and @command{rm}
+If the @option{-I} or @option{--interactive=once} option is given,
+and there are more than three files or the @option{-r}, @option{-R},
+or @option{--recursive} are given, then @command{rm} prompts the user
+for whether to proceed with the entire operation. If the response is
+not affirmative, the entire command is aborted.
+
+Otherwise, if a file is unwritable, standard input is a terminal, and
+the @option{-f} or @option{--force} option is not given, or the
+@option{-i} or @option{--interactive=always} option @emph{is} given,
+@command{rm} prompts the user for whether to remove the file.
+If the response is not affirmative, the file is skipped.
+
+Any attempt to remove a file whose last file name component is
+@file{.} or @file{..} is rejected without any prompting.
+
+@emph{Warning}: If you use @command{rm} to remove a file, it is usually
+possible to recover the contents of that file. If you want more assurance
+that the contents are truly unrecoverable, consider using @command{shred}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+Ignore nonexistent files and never prompt the user.
+Ignore any previous @option{--interactive} (@option{-i}) option.
+
+@item -i
+@opindex -i
+Prompt whether to remove each file.
+If the response is not affirmative, the file is skipped.
+Ignore any previous @option{--force} (@option{-f}) option.
+Equivalent to @option{--interactive=always}.
+
+@item -I
+@opindex -I
+Prompt once whether to proceed with the command, if more than three
+files are named or if a recursive removal is requested. Ignore any
+previous @option{--force} (@option{-f}) option. Equivalent to
+@option{--interactive=once}.
+
+@itemx --interactive [=@var{when}]
+@opindex --interactive
+Specify when to issue an interactive prompt. @var{when} may be
+omitted, or one of:
+@itemize @bullet
+@item never
+@vindex never @r{interactive option}
+- Do not prompt at all.
+@item once
+@vindex once @r{interactive option}
+- Prompt once if more than three files are named or if a recursive
+removal is requested. Equivalent to @option{-I}.
+@item always
+@vindex always @r{interactive option}
+- Prompt for every file being removed. Equivalent to @option{-i}.
+@end itemize
+@option{--interactive} with no @var{when} is equivalent to
+@option{--interactive=always}.
+
+@itemx --one-file-system
+@opindex --one-file-system
+@cindex one file system, restricting @command{rm} to
+When removing a hierarchy recursively, skip any directory that is on a
+file system different from that of the corresponding command line argument.
+
+This option is useful when removing a build ``chroot'' hierarchy,
+which normally contains no valuable data. However, it is not uncommon
+to bind-mount @file{/home} into such a hierarchy, to make it easier to
+use one's start-up file. The catch is that it's easy to forget to
+unmount @file{/home}. Then, when you use @command{rm -rf} to remove
+your normally throw-away chroot, that command will remove everything
+under @file{/home}, too.
+Use the @option{--one-file-system} option, and it will
+warn about and skip directories on other file systems.
+Of course, this will not save your @file{/home} if it and your
+chroot happen to be on the same file system.
+
+@itemx --preserve-root
+@opindex --preserve-root
+@cindex root directory, disallow recursive destruction
+Fail upon any attempt to remove the root directory, @file{/},
+when used with the @option{--recursive} option.
+This is the default behavior.
+@xref{Treating / specially}.
+
+@itemx --no-preserve-root
+@opindex --no-preserve-root
+@cindex root directory, allow recursive destruction
+Do not treat @file{/} specially when removing recursively.
+This option is not recommended unless you really want to
+remove all the files on your computer.
+@xref{Treating / specially}.
+
+@item -r
+@itemx -R
+@itemx --recursive
+@opindex -r
+@opindex -R
+@opindex --recursive
+@cindex directories, removing (recursively)
+Remove the listed directories and their contents recursively.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file before removing it.
+
+@end table
+
+@cindex files beginning with @samp{-}, removing
+@cindex @samp{-}, removing files beginning with
+One common question is how to remove files whose names begin with a
+@samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
+function to parse its arguments, lets you use the @samp{--} option to
+indicate that all following arguments are non-options. To remove a file
+called @file{-f} in the current directory, you could type either:
+
+@example
+rm -- -f
+@end example
+
+@noindent
+or:
+
+@example
+rm ./-f
+@end example
+
+@opindex - @r{and Unix @command{rm}}
+The Unix @command{rm} program's use of a single @samp{-} for this purpose
+predates the development of the getopt standard syntax.
+
+@exitstatus
+
+
+@node shred invocation
+@section @command{shred}: Remove files more securely
+
+@pindex shred
+@cindex data, erasing
+@cindex erasing data
+
+@command{shred} overwrites devices or files, to help prevent even
+very expensive hardware from recovering the data.
+
+Ordinarily when you remove a file (@pxref{rm invocation}), the data is
+not actually destroyed. Only the index listing where the file is
+stored is destroyed, and the storage is made available for reuse.
+There are undelete utilities that will attempt to reconstruct the index
+and can bring the file back if the parts were not reused.
+
+On a busy system with a nearly-full drive, space can get reused in a few
+seconds. But there is no way to know for sure. If you have sensitive
+data, you may want to be sure that recovery is not possible by actually
+overwriting the file with non-sensitive data.
+
+However, even after doing that, it is possible to take the disk back
+to a laboratory and use a lot of sensitive (and expensive) equipment
+to look for the faint ``echoes'' of the original data underneath the
+overwritten data. If the data has only been overwritten once, it's not
+even that hard.
+
+The best way to remove something irretrievably is to destroy the media
+it's on with acid, melt it down, or the like. For cheap removable media
+like floppy disks, this is the preferred method. However, hard drives
+are expensive and hard to melt, so the @command{shred} utility tries
+to achieve a similar effect non-destructively.
+
+This uses many overwrite passes, with the data patterns chosen to
+maximize the damage they do to the old data. While this will work on
+floppies, the patterns are designed for best effect on hard drives.
+For more details, see the source code and Peter Gutmann's paper
+@uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
+@cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
+from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
+California, July 22--25, 1996).
+
+@strong{Please note} that @command{shred} relies on a very important assumption:
+that the file system overwrites data in place. This is the traditional
+way to do things, but many modern file system designs do not satisfy this
+assumption. Exceptions include:
+
+@itemize @bullet
+
+@item
+Log-structured or journaled file systems, such as those supplied with
+AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
+BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
+
+@item
+File systems that write redundant data and carry on even if some writes
+fail, such as RAID-based file systems.
+
+@item
+File systems that make snapshots, such as Network Appliance's NFS server.
+
+@item
+File systems that cache in temporary locations, such as NFS version 3
+clients.
+
+@item
+Compressed file systems.
+@end itemize
+
+In the particular case of ext3 file systems, the above disclaimer applies (and
+@command{shred} is thus of limited effectiveness) only in @code{data=journal}
+mode, which journals file data in addition to just metadata. In both
+the @code{data=ordered} (default) and @code{data=writeback} modes,
+@command{shred} works as usual. Ext3 journaling modes can be changed
+by adding the @code{data=something} option to the mount options for a
+particular file system in the @file{/etc/fstab} file, as documented in
+the mount man page (man mount).
+
+If you are not sure how your file system operates, then you should assume
+that it does not overwrite data in place, which means that shred cannot
+reliably operate on regular files in your file system.
+
+Generally speaking, it is more reliable to shred a device than a file,
+since this bypasses the problem of file system design mentioned above.
+However, even shredding devices is not always completely reliable. For
+example, most disks map out bad sectors invisibly to the application; if
+the bad sectors contain sensitive data, @command{shred} won't be able to
+destroy it.
+
+@command{shred} makes no attempt to detect or report this problem, just as
+it makes no attempt to do anything about backups. However, since it is
+more reliable to shred devices than files, @command{shred} by default does
+not truncate or remove the output file. This default is more suitable
+for devices, which typically cannot be truncated and should not be
+removed.
+
+Finally, consider the risk of backups and mirrors.
+File system backups and remote mirrors may contain copies of the
+file that cannot be removed, and that will allow a shredded file
+to be recovered later. So if you keep any data you may later want
+to destroy using @command{shred}, be sure that it is not backed up or mirrored.
+
+@example
+shred [@var{option}]@dots{} @var{file}[@dots{}]
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+@cindex force deletion
+Override file permissions if necessary to allow overwriting.
+
+@item -@var{number}
+@itemx -n @var{number}
+@itemx --iterations=@var{number}
+@opindex -n @var{number}
+@opindex --iterations=@var{number}
+@cindex iterations, selecting the number of
+By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
+overwrite. You can reduce this to save time, or increase it if you think it's
+appropriate. After 25 passes all of the internal overwrite patterns will have
+been used at least once.
+
+@item --random-source=@var{file}
+@opindex --random-source
+@cindex random source for shredding
+Use @var{file} as a source of random data used to overwrite and to
+choose pass ordering. @xref{Random sources}.
+
+@item -s @var{bytes}
+@itemx --size=@var{bytes}
+@opindex -s @var{bytes}
+@opindex --size=@var{bytes}
+@cindex size of file to shred
+Shred the first @var{bytes} bytes of the file. The default is to shred
+the whole file. @var{bytes} can be followed by a size specification like
+@samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
+
+@item -u
+@itemx --remove
+@opindex -u
+@opindex --remove
+@cindex removing files after shredding
+After shredding a file, truncate it (if possible) and then remove it.
+If a file has multiple links, only the named links will be removed.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Display to standard error all status updates as sterilization proceeds.
+
+@item -x
+@itemx --exact
+@opindex -x
+@opindex --exact
+By default, @command{shred} rounds the size of a regular file up to the next
+multiple of the file system block size to fully erase the last block of the file.
+Use @option{--exact} to suppress that behavior.
+Thus, by default if you shred a 10-byte regular file on a system with 512-byte
+blocks, the resulting file will be 512 bytes long. With this option,
+shred does not increase the apparent size of the file.
+
+@item -z
+@itemx --zero
+@opindex -z
+@opindex --zero
+Normally, the last pass that @command{shred} writes is made up of
+random data. If this would be conspicuous on your hard drive (for
+example, because it looks like encrypted data), or you just think
+it's tidier, the @option{--zero} option adds an additional overwrite pass with
+all zero bits. This is in addition to the number of passes specified
+by the @option{--iterations} option.
+
+@end table
+
+You might use the following command to erase all trace of the
+file system you'd created on the floppy disk in your first drive.
+That command takes about 20 minutes to erase a ``1.44MB'' (actually
+1440 KiB) floppy.
+
+@example
+shred --verbose /dev/fd0
+@end example
+
+Similarly, to erase all data on a selected partition of
+your hard disk, you could give a command like this:
+
+@example
+shred --verbose /dev/sda5
+@end example
+
+A @var{file} of @samp{-} denotes standard output.
+The intended use of this is to shred a removed temporary file.
+For example:
+
+@example
+i=`tempfile -m 0600`
+exec 3<>"$i"
+rm -- "$i"
+echo "Hello, world" >&3
+shred - >&3
+exec 3>-
+@end example
+
+However, the command @samp{shred - >file} does not shred the contents
+of @var{file}, since the shell truncates @var{file} before invoking
+@command{shred}. Use the command @samp{shred file} or (if using a
+Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
+
+@exitstatus
+
+
+@node Special file types
+@chapter Special file types
+
+@cindex special file types
+@cindex file types, special
+
+This chapter describes commands which create special types of files (and
+@command{rmdir}, which removes directories, one special file type).
+
+@cindex special file types
+@cindex file types
+Although Unix-like operating systems have markedly fewer special file
+types than others, not @emph{everything} can be treated only as the
+undifferentiated byte stream of @dfn{normal files}. For example, when a
+file is created or removed, the system must record this information,
+which it does in a @dfn{directory}---a special type of file. Although
+you can read directories as normal files, if you're curious, in order
+for the system to do its job it must impose a structure, a certain
+order, on the bytes of the file. Thus it is a ``special'' type of file.
+
+Besides directories, other special file types include named pipes
+(FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
+
+@menu
+* link invocation:: Make a hard link via the link syscall
+* ln invocation:: Make links between files.
+* mkdir invocation:: Make directories.
+* mkfifo invocation:: Make FIFOs (named pipes).
+* mknod invocation:: Make block or character special files.
+* readlink invocation:: Print the referent of a symbolic link.
+* rmdir invocation:: Remove empty directories.
+* unlink invocation:: Remove files via the unlink syscall
+@end menu
+
+
+@node link invocation
+@section @command{link}: Make a hard link via the link syscall
+
+@pindex link
+@cindex links, creating
+@cindex hard links, creating
+@cindex creating links (hard only)
+
+@command{link} creates a single hard link at a time.
+It is a minimalist interface to the system-provided
+@code{link} function. @xref{Hard Links, , , libc,
+The GNU C Library Reference Manual}.
+It avoids the bells and whistles of the more commonly-used
+@command{ln} command (@pxref{ln invocation}).
+Synopsis:
+
+@example
+link @var{filename} @var{linkname}
+@end example
+
+@var{filename} must specify an existing file, and @var{linkname}
+must specify a nonexistent entry in an existing directory.
+@command{link} simply calls @code{link (@var{filename}, @var{linkname})}
+to create the link.
+
+On a @acronym{GNU} system, this command acts like @samp{ln --directory
+--no-target-directory @var{filename} @var{linkname}}. However, the
+@option{--directory} and @option{--no-target-directory} options are
+not specified by @acronym{POSIX}, and the @command{link} command is
+more portable in practice.
+
+@exitstatus
+
+
+@node ln invocation
+@section @command{ln}: Make links between files
+
+@pindex ln
+@cindex links, creating
+@cindex hard links, creating
+@cindex symbolic (soft) links, creating
+@cindex creating links (hard or soft)
+
+@cindex file systems and hard links
+@command{ln} makes links between files. By default, it makes hard links;
+with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
+Synopses:
+
+@example
+ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
+ln [@var{option}]@dots{} @var{target}
+ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
+ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
+@end example
+
+@itemize @bullet
+
+@item
+If two file names are given, @command{ln} creates a link to the first
+file from the second.
+
+@item
+If one @var{target} is given, @command{ln} creates a link to that file
+in the current directory.
+
+@item
+If the @option{--target-directory} (@option{-t}) option is given, or
+failing that if the last file is a directory and the
+@option{--no-target-directory} (@option{-T}) option is not given,
+@command{ln} creates a link to each @var{target} file in the specified
+directory, using the @var{target}s' names.
+
+@end itemize
+
+Normally @command{ln} does not remove existing files. Use the
+@option{--force} (@option{-f}) option to remove them unconditionally,
+the @option{--interactive} (@option{-i}) option to remove them
+conditionally, and the @option{--backup} (@option{-b}) option to
+rename them.
+
+@cindex hard link, defined
+@cindex inode, and hard links
+A @dfn{hard link} is another name for an existing file; the link and the
+original are indistinguishable. Technically speaking, they share the
+same inode, and the inode contains all the information about a
+file---indeed, it is not incorrect to say that the inode @emph{is} the
+file. On all existing implementations, you cannot make a hard link to
+a directory, and hard links cannot cross file system boundaries. (These
+restrictions are not mandated by @acronym{POSIX}, however.)
+
+@cindex dereferencing symbolic links
+@cindex symbolic link, defined
+@dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
+a special file type (which not all kernels support: System V release 3
+(and older) systems lack symlinks) in which the link file actually
+refers to a different file, by name. When most operations (opening,
+reading, writing, and so on) are passed the symbolic link file, the
+kernel automatically @dfn{dereferences} the link and operates on the
+target of the link. But some operations (e.g., removing) work on the
+link file itself, rather than on its target. The owner, group, and
+mode of a symlink are not significant to file access performed through
+the link. @xref{Symbolic Links,,,
+libc, The GNU C Library Reference Manual}.
+
+Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
+occurs when the string in the symlink does not resolve to a file.
+There are no restrictions against creating dangling symbolic links.
+There are trade-offs to using absolute or relative symlinks. An
+absolute symlink always points to the same file, even if the directory
+containing the link is moved. However, if the symlink is visible from
+more than one machine (such as on a networked file system), the file
+pointed to might not always be the same. A relative symbolic link is
+resolved in relation to the directory that contains the link, and is
+often useful in referring to files on the same device without regards
+to what name that device is mounted on when accessed via networked
+machines.
+
+When creating a relative symlink in a different location than the
+current directory, the resolution of the symlink will be different
+than the resolution of the same string from the current directory.
+Therefore, many users prefer to first change directories to the
+location where the relative symlink will be created, so that
+tab-completion or other file resolution will find the same target as
+what will be placed in the symlink.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@optBackup
+
+@item -d
+@itemx -F
+@itemx --directory
+@opindex -d
+@opindex -F
+@opindex --directory
+@cindex hard links to directories
+Allow users with appropriate privileges to attempt to make hard links
+to directories.
+However, note that this will probably fail due to
+system restrictions, even for the super-user.
+
+@item -f
+@itemx --force
+@opindex -f
+@opindex --force
+Remove existing destination files.
+
+@item -i
+@itemx --interactive
+@opindex -i
+@opindex --interactive
+@cindex prompting, and @command{ln}
+Prompt whether to remove existing destination files.
+
+@item -n
+@itemx --no-dereference
+@opindex -n
+@opindex --no-dereference
+Do not treat the last operand specially when it is a symbolic link to
+a directory. Instead, treat it as if it were a normal file.
+
+When the destination is an actual directory (not a symlink to one),
+there is no ambiguity. The link is created in that directory.
+But when the specified destination is a symlink to a directory,
+there are two ways to treat the user's request. @command{ln} can
+treat the destination just as it would a normal directory and create
+the link in it. On the other hand, the destination can be viewed as a
+non-directory---as the symlink itself. In that case, @command{ln}
+must delete or backup that symlink before creating the new link.
+The default is to treat a destination that is a symlink to a directory
+just like a directory.
+
+This option is weaker than the @option{--no-target-directory}
+(@option{-T}) option, so it has no effect if both options are given.
+
+@item -s
+@itemx --symbolic
+@opindex -s
+@opindex --symbolic
+Make symbolic links instead of hard links. This option merely produces
+an error message on systems that do not support symbolic links.
+
+@optBackupSuffix
+
+@optTargetDirectory
+
+@optNoTargetDirectory
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print the name of each file after linking it successfully.
+
+@end table
+
+@exitstatus
+
+Examples:
+
+@smallexample
+Bad Example:
+
+# Create link ../a pointing to a in that directory.
+# Not really useful because it points to itself.
+ln -s a ..
+
+Better Example:
+
+# Change to the target before creating symlinks to avoid being confused.
+cd ..
+ln -s adir/a .
+
+Bad Example:
+
+# Hard coded file names don't move well.
+ln -s $(pwd)/a /some/dir/
+
+Better Example:
+
+# Relative file names survive directory moves and also
+# work across networked file systems.
+ln -s afile anotherfile
+ln -s ../adir/afile yetanotherfile
+@end smallexample
+
+
+@node mkdir invocation
+@section @command{mkdir}: Make directories
+
+@pindex mkdir
+@cindex directories, creating
+@cindex creating directories
+
+@command{mkdir} creates directories with the specified names. Synopsis:
+
+@example
+mkdir [@var{option}]@dots{} @var{name}@dots{}
+@end example
+
+@command{mkdir} creates each directory @var{name} in the order given.
+It reports an error if @var{name} already exists, unless the
+@option{-p} option is given and @var{name} is a directory.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex modes of created directories, setting
+Set the file permission bits of created directories to @var{mode},
+which uses the same syntax as
+in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
+everyone) for the point of the departure. @xref{File permissions}.
+
+Normally the directory has the desired file mode bits at the moment it
+is created. As a @acronym{GNU} extension, @var{mode} may also mention
+special mode bits, but in this case there may be a temporary window
+during which the directory exists but its special mode bits are
+incorrect. @xref{Directory Setuid and Setgid}, for how the
+set-user-ID and set-group-ID bits of directories are inherited unless
+overridden in this way.
+
+@item -p
+@itemx --parents
+@opindex -p
+@opindex --parents
+@cindex parent directories, creating
+Make any missing parent directories for each argument, setting their
+file permission bits to the umask modified by @samp{u+wx}. Ignore
+existing parent directories, and do not change their file permission
+bits.
+
+To set the file permission bits of any newly-created parent
+directories to a value that includes @samp{u+wx}, you can set the
+umask before invoking @command{mkdir}. For example, if the shell
+command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
+@file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
+To set a parent's special mode bits as well, you can invoke
+@command{chmod} after @command{mkdir}. @xref{Directory Setuid and
+Setgid}, for how the set-user-ID and set-group-ID bits of
+newly-created parent directories are inherited.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Print a message for each created directory. This is most useful with
+@option{--parents}.
+@end table
+
+@exitstatus
+
+
+@node mkfifo invocation
+@section @command{mkfifo}: Make FIFOs (named pipes)
+
+@pindex mkfifo
+@cindex FIFOs, creating
+@cindex named pipes, creating
+@cindex creating FIFOs (named pipes)
+
+@command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
+specified names. Synopsis:
+
+@example
+mkfifo [@var{option}] @var{name}@dots{}
+@end example
+
+A @dfn{FIFO} is a special file type that permits independent processes
+to communicate. One process opens the FIFO file for writing, and
+another for reading, after which data can flow as with the usual
+anonymous pipe in shells or elsewhere.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+@cindex modes of created FIFOs, setting
+Set the mode of created FIFOs to @var{mode}, which is symbolic as in
+@command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
+for the point of departure. @var{mode} should specify only file
+permission bits. @xref{File permissions}.
+
+@end table
+
+@exitstatus
+
+
+@node mknod invocation
+@section @command{mknod}: Make block or character special files
+
+@pindex mknod
+@cindex block special files, creating
+@cindex character special files, creating
+
+@command{mknod} creates a FIFO, character special file, or block special
+file with the specified name. Synopsis:
+
+@example
+mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
+@end example
+
+@cindex special files
+@cindex block special files
+@cindex character special files
+Unlike the phrase ``special file type'' above, the term @dfn{special
+file} has a technical meaning on Unix: something that can generate or
+receive data. Usually this corresponds to a physical piece of hardware,
+e.g., a printer or a disk. (These files are typically created at
+system-configuration time.) The @command{mknod} command is what creates
+files of this type. Such devices can be read either a character at a
+time or a ``block'' (many characters) at a time, hence we say there are
+@dfn{block special} files and @dfn{character special} files.
+
+@c mknod is a shell built-in at least with OpenBSD's /bin/sh
+@mayConflictWithShellBuiltIn{mknod}
+
+The arguments after @var{name} specify the type of file to make:
+
+@table @samp
+
+@item p
+@opindex p @r{for FIFO file}
+for a FIFO
+
+@item b
+@opindex b @r{for block special file}
+for a block special file
+
+@item c
+@c Don't document the `u' option -- it's just a synonym for `c'.
+@c Do *any* versions of mknod still use it?
+@c @itemx u
+@opindex c @r{for character special file}
+@c @opindex u @r{for character special file}
+for a character special file
+
+@end table
+
+When making a block or character special file, the major and minor
+device numbers must be given after the file type.
+If a major or minor device number begins with @samp{0x} or @samp{0X},
+it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
+as octal; otherwise, as decimal.
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -m @var{mode}
+@itemx --mode=@var{mode}
+@opindex -m
+@opindex --mode
+Set the mode of created files to @var{mode}, which is symbolic as in
+@command{chmod} and uses @samp{a=rw} as the point of departure.
+@var{mode} should specify only file permission bits.
+@xref{File permissions}.
+
+@end table
+
+@exitstatus
+
+
+@node readlink invocation
+@section @command{readlink}: Print the referent of a symbolic link
+
+@pindex readlink
+@cindex displaying value of a symbolic link
+
+@command{readlink} may work in one of two supported modes:
+
+@table @samp
+
+@item Readlink mode
+
+@command{readlink} outputs the value of the given symbolic link.
+If @command{readlink} is invoked with an argument other than the name
+of a symbolic link, it produces no output and exits with a nonzero exit code.
+
+@item Canonicalize mode
+
+@command{readlink} outputs the absolute name of the given file which contains
+no @file{.}, @file{..} components nor any repeated separators
+(@file{/}) or symbolic links.
+
+@end table
+
+@example
+readlink [@var{option}] @var{file}
+@end example
+
+By default, @command{readlink} operates in readlink mode.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -f
+@itemx --canonicalize
+@opindex -f
+@opindex --canonicalize
+Activate canonicalize mode.
+If any component of the file name except the last one is missing or unavailable,
+@command{readlink} produces no output and exits with a nonzero exit code.
+
+@item -e
+@itemx --canonicalize-existing
+@opindex -e
+@opindex --canonicalize-existing
+Activate canonicalize mode.
+If any component is missing or unavailable, @command{readlink} produces
+no output and exits with a nonzero exit code.
+
+@item -m
+@itemx --canonicalize-missing
+@opindex -m
+@opindex --canonicalize-missing
+Activate canonicalize mode.
+If any component is missing or unavailable, @command{readlink} treats it
+as a directory.
+
+@item -n
+@itemx --no-newline
+@opindex -n
+@opindex --no-newline
+Do not output the trailing newline.
+
+@item -s
+@itemx -q
+@itemx --silent
+@itemx --quiet
+@opindex -s
+@opindex -q
+@opindex --silent
+@opindex --quiet
+Suppress most error messages.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Report error messages.
+
+@end table
+
+The @command{readlink} utility first appeared in OpenBSD 2.1.
+
+@exitstatus
+
+
+@node rmdir invocation
+@section @command{rmdir}: Remove empty directories
+
+@pindex rmdir
+@cindex removing empty directories
+@cindex directories, removing empty
+
+@command{rmdir} removes empty directories. Synopsis:
+
+@example
+rmdir [@var{option}]@dots{} @var{directory}@dots{}
+@end example
+
+If any @var{directory} argument does not refer to an existing empty
+directory, it is an error.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item --ignore-fail-on-non-empty
+@opindex --ignore-fail-on-non-empty
+@cindex directory deletion, ignoring failures
+Ignore each failure to remove a directory that is solely because
+the directory is non-empty.
+
+@item -p
+@itemx --parents
+@opindex -p
+@opindex --parents
+@cindex parent directories, removing
+Remove @var{directory}, then try to remove each component of @var{directory}.
+So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
+As such, it fails if any of those directories turns out not to be empty.
+Use the @option{--ignore-fail-on-non-empty} option to make it so such
+a failure does not evoke a diagnostic and does not cause @command{rmdir} to
+exit unsuccessfully.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+@cindex directory deletion, reporting
+Give a diagnostic for each successful removal.
+@var{directory} is removed.
+
+@end table
+
+@xref{rm invocation}, for how to remove non-empty directories (recursively).
+
+@exitstatus
+
+
+@node unlink invocation
+@section @command{unlink}: Remove files via the unlink syscall
+
+@pindex unlink
+@cindex removing files or directories (via the unlink syscall)
+
+@command{unlink} deletes a single specified file name.
+It is a minimalist interface to the system-provided
+@code{unlink} function. @xref{Deleting Files, , , libc,
+The GNU C Library Reference Manual}. Synopsis:
+It avoids the bells and whistles of the more commonly-used
+@command{rm} command (@pxref{rm invocation}).
+
+@example
+unlink @var{filename}
+@end example
+
+On some systems @code{unlink} can be used to delete the name of a
+directory. On others, it can be used that way only by a privileged user.
+In the GNU system @code{unlink} can never delete the name of a directory.
+
+The @command{unlink} command honors the @option{--help} and
+@option{--version} options. To remove a file whose name begins with
+@samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
+
+@exitstatus
+
+
+@node Changing file attributes
+@chapter Changing file attributes
+
+@cindex changing file attributes
+@cindex file attributes, changing
+@cindex attributes, file
+
+A file is not merely its contents, a name, and a file type
+(@pxref{Special file types}). A file also has an owner (a user ID), a
+group (a group ID), permissions (what the owner can do with the file,
+what people in the group can do, and what everyone else can do), various
+timestamps, and other information. Collectively, we call these a file's
+@dfn{attributes}.
+
+These commands change file attributes.
+
+@menu
+* chgrp invocation:: Change file groups.
+* chmod invocation:: Change access permissions.
+* chown invocation:: Change file owners and groups.
+* touch invocation:: Change file timestamps.
+@end menu
+
+
+@node chown invocation
+@section @command{chown}: Change file owner and group
+
+@pindex chown
+@cindex file ownership, changing
+@cindex group ownership, changing
+@cindex changing file ownership
+@cindex changing group ownership
+
+@command{chown} changes the user and/or group ownership of each given @var{file}
+to @var{new-owner} or to the user and group of an existing reference file.
+Synopsis:
+
+@example
+chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+If used, @var{new-owner} specifies the new owner and/or group as follows
+(with no embedded white space):
+
+@example
+[@var{owner}] [ : [@var{group}] ]
+@end example
+
+Specifically:
+
+@table @var
+@item owner
+If only an @var{owner} (a user name or numeric user ID) is given, that
+user is made the owner of each given file, and the files' group is not
+changed.
+
+@item owner@samp{:}group
+If the @var{owner} is followed by a colon and a @var{group} (a
+group name or numeric group ID), with no spaces between them, the group
+ownership of the files is changed as well (to @var{group}).
+
+@item owner@samp{:}
+If a colon but no group name follows @var{owner}, that user is
+made the owner of the files and the group of the files is changed to
+@var{owner}'s login group.
+
+@item @samp{:}group
+If the colon and following @var{group} are given, but the owner
+is omitted, only the group of the files is changed; in this case,
+@command{chown} performs the same function as @command{chgrp}.
+
+@item @samp{:}
+If only a colon is given, or if @var{new-owner} is empty, neither the
+owner nor the group is changed.
+
+@end table
+
+If @var{owner} or @var{group} is intended to represent a numeric user
+or group ID, then you may specify it with a leading @samp{+}.
+@xref{Disambiguating names and IDs}.
+
+Some older scripts may still use @samp{.} in place of the @samp{:} separator.
+@acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
+require support for that, but for backward compatibility @acronym{GNU}
+@command{chown} supports @samp{.} so long as no ambiguity results.
+New scripts should avoid the use of @samp{.} because it is not
+portable, and because it has undesirable results if the entire
+@var{owner@samp{.}group} happens to identify a user whose name
+contains @samp{.}.
+
+The @command{chown} command sometimes clears the set-user-ID or
+set-group-ID permission bits. This behavior depends on the policy and
+functionality of the underlying @code{chown} system call, which may
+make system-dependent file mode modifications outside the control of
+the @command{chown} command. For example, the @command{chown} command
+might not affect those bits when invoked by a user with appropriate
+privileges, or when the
+bits signify some function other than executable permission (e.g.,
+mandatory locking).
+When in doubt, check the underlying system behavior.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+@cindex changed owners, verbosely describing
+Verbosely describe the action for each @var{file} whose ownership
+actually changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose ownership cannot be
+changed.
+
+@itemx @w{@kbd{--from}=@var{old-owner}}
+@opindex --from
+@cindex symbolic links, changing owner
+Change a @var{file}'s ownership only if it has current attributes specified
+by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
+described above.
+This option is useful primarily from a security standpoint in that
+it narrows considerably the window of potential abuse.
+For example, to reflect a user ID numbering change for one user's files
+without an option like this, @code{root} might run
+
+@smallexample
+find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
+@end smallexample
+
+But that is dangerous because the interval between when the @command{find}
+tests the existing file's owner and when the @command{chown} is actually run
+may be quite large.
+One way to narrow the gap would be to invoke chown for each file
+as it is found:
+
+@example
+find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
+@end example
+
+But that is very slow if there are many affected files.
+With this option, it is safer (the gap is narrower still)
+though still not perfect:
+
+@example
+chown -h -R --from=OLDUSER NEWUSER /
+@end example
+
+@item --dereference
+@opindex --dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Do not act on symbolic links themselves but rather on what they point to.
+This is the default.
+
+@item -h
+@itemx --no-dereference
+@opindex -h
+@opindex --no-dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Act on symbolic links themselves instead of what they point to.
+This mode relies on the @code{lchown} system call.
+On systems that do not provide the @code{lchown} system call,
+@command{chown} fails when a file specified on the command line
+is a symbolic link.
+By default, no diagnostic is issued for symbolic links encountered
+during a recursive traversal, but see @option{--verbose}.
+
+@itemx --preserve-root
+@opindex --preserve-root
+@cindex root directory, disallow recursive modification
+Fail upon any attempt to recursively change the root directory, @file{/}.
+Without @option{--recursive}, this option has no effect.
+@xref{Treating / specially}.
+
+@itemx --no-preserve-root
+@opindex --no-preserve-root
+@cindex root directory, allow recursive modification
+Cancel the effect of any preceding @option{--preserve-root} option.
+@xref{Treating / specially}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the user and group of each @var{file} to be the same as those of
+@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
+user and group of the symbolic link, but rather those of the file it
+refers to.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Output a diagnostic for every file processed.
+If a symbolic link is encountered during a recursive traversal
+on a system without the @code{lchown} system call, and @option{--no-dereference}
+is in effect, then issue a diagnostic saying neither the symbolic link nor
+its referent is being changed.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing file ownership
+Recursively change ownership of directories and their contents.
+
+@choptH
+@xref{Traversing symlinks}.
+
+@choptL
+@xref{Traversing symlinks}.
+
+@choptP
+@xref{Traversing symlinks}.
+
+@end table
+
+@exitstatus
+
+Examples:
+
+@smallexample
+# Change the owner of /u to "root".
+chown root /u
+
+# Likewise, but also change its group to "staff".
+chown root:staff /u
+
+# Change the owner of /u and subfiles to "root".
+chown -hR root /u
+@end smallexample
+
+
+@node chgrp invocation
+@section @command{chgrp}: Change group ownership
+
+@pindex chgrp
+@cindex group ownership, changing
+@cindex changing group ownership
+
+@command{chgrp} changes the group ownership of each given @var{file}
+to @var{group} (which can be either a group name or a numeric group ID)
+or to the group of an existing reference file. Synopsis:
+
+@example
+chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+If @var{group} is intended to represent a
+numeric group ID, then you may specify it with a leading @samp{+}.
+@xref{Disambiguating names and IDs}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+@cindex changed files, verbosely describing
+Verbosely describe the action for each @var{file} whose group actually
+changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose group cannot be
+changed.
+
+@item --dereference
+@opindex --dereference
+@cindex symbolic links, changing owner
+@findex lchown
+Do not act on symbolic links themselves but rather on what they point to.
+This is the default.
+
+@item -h
+@itemx --no-dereference
+@opindex -h
+@opindex --no-dereference
+@cindex symbolic links, changing group
+@findex lchown
+Act on symbolic links themselves instead of what they point to.
+This mode relies on the @code{lchown} system call.
+On systems that do not provide the @code{lchown} system call,
+@command{chgrp} fails when a file specified on the command line
+is a symbolic link.
+By default, no diagnostic is issued for symbolic links encountered
+during a recursive traversal, but see @option{--verbose}.
+
+@itemx --preserve-root
+@opindex --preserve-root
+@cindex root directory, disallow recursive modification
+Fail upon any attempt to recursively change the root directory, @file{/}.
+Without @option{--recursive}, this option has no effect.
+@xref{Treating / specially}.
+
+@itemx --no-preserve-root
+@opindex --no-preserve-root
+@cindex root directory, allow recursive modification
+Cancel the effect of any preceding @option{--preserve-root} option.
+@xref{Treating / specially}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the group of each @var{file} to be the same as that of
+@var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
+group of the symbolic link, but rather that of the file it refers to.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Output a diagnostic for every file processed.
+If a symbolic link is encountered during a recursive traversal
+on a system without the @code{lchown} system call, and @option{--no-dereference}
+is in effect, then issue a diagnostic saying neither the symbolic link nor
+its referent is being changed.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing group ownership
+Recursively change the group ownership of directories and their contents.
+
+@choptH
+@xref{Traversing symlinks}.
+
+@choptL
+@xref{Traversing symlinks}.
+
+@choptP
+@xref{Traversing symlinks}.
+
+@end table
+
+@exitstatus
+
+Examples:
+
+@smallexample
+# Change the group of /u to "staff".
+chgrp staff /u
+
+# Change the group of /u and subfiles to "staff".
+chgrp -hR staff /u
+@end smallexample
+
+
+@node chmod invocation
+@section @command{chmod}: Change access permissions
+
+@pindex chmod
+@cindex changing access permissions
+@cindex access permissions, changing
+@cindex permissions, changing access
+
+@command{chmod} changes the access permissions of the named files. Synopsis:
+
+@example
+chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
+@end example
+
+@cindex symbolic links, permissions of
+@command{chmod} never changes the permissions of symbolic links, since
+the @command{chmod} system call cannot change their permissions.
+This is not a problem since the permissions of symbolic links are
+never used. However, for each symbolic link listed on the command
+line, @command{chmod} changes the permissions of the pointed-to file.
+In contrast, @command{chmod} ignores symbolic links encountered during
+recursive directory traversals.
+
+A successful use of @command{chmod} clears the set-group-ID bit of a
+regular file if the file's group ID does not match the user's
+effective group ID or one of the user's supplementary group IDs,
+unless the user has appropriate privileges. Additional restrictions
+may cause the set-user-ID and set-group-ID bits of @var{mode} or
+@var{ref_file} to be ignored. This behavior depends on the policy and
+functionality of the underlying @code{chmod} system call. When in
+doubt, check the underlying system behavior.
+
+If used, @var{mode} specifies the new file mode bits.
+For details, see the section on @ref{File permissions}.
+If you really want @var{mode} to have a leading @samp{-}, you should
+use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
+though, @samp{chmod a-w file} is preferable, and @command{chmod -w
+file} (without the @option{--}) complains if it behaves differently
+from what @samp{chmod a-w file} would do.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --changes
+@opindex -c
+@opindex --changes
+Verbosely describe the action for each @var{file} whose permissions
+actually changes.
+
+@item -f
+@itemx --silent
+@itemx --quiet
+@opindex -f
+@opindex --silent
+@opindex --quiet
+@cindex error messages, omitting
+Do not print error messages about files whose permissions cannot be
+changed.
+
+@itemx --preserve-root
+@opindex --preserve-root
+@cindex root directory, disallow recursive modification
+Fail upon any attempt to recursively change the root directory, @file{/}.
+Without @option{--recursive}, this option has no effect.
+@xref{Treating / specially}.
+
+@itemx --no-preserve-root
+@opindex --no-preserve-root
+@cindex root directory, allow recursive modification
+Cancel the effect of any preceding @option{--preserve-root} option.
+@xref{Treating / specially}.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+Verbosely describe the action or non-action taken for every @var{file}.
+
+@item --reference=@var{ref_file}
+@opindex --reference
+Change the mode of each @var{file} to be the same as that of @var{ref_file}.
+@xref{File permissions}.
+If @var{ref_file} is a symbolic link, do not use the mode
+of the symbolic link, but rather that of the file it refers to.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+@cindex recursively changing access permissions
+Recursively change permissions of directories and their contents.
+
+@end table
+
+@exitstatus
+
+
+@node touch invocation
+@section @command{touch}: Change file timestamps
+
+@pindex touch
+@cindex changing file timestamps
+@cindex file timestamps, changing
+@cindex timestamps, changing file
+
+@command{touch} changes the access and/or modification times of the
+specified files. Synopsis:
+
+@example
+touch [@var{option}]@dots{} @var{file}@dots{}
+@end example
+
+@cindex empty files, creating
+Any @var{file} argument that does not exist is created empty.
+
+A @var{file} argument string of @samp{-} is handled specially and
+causes @command{touch} to change the times of the file associated with
+standard output.
+
+@cindex permissions, for changing file timestamps
+If changing both the access and modification times to the current
+time, @command{touch} can change the timestamps for files that the user
+running it does not own but has write permission for. Otherwise, the
+user must own the files.
+
+Although @command{touch} provides options for changing two of the times---the
+times of last access and modification---of a file, there is actually
+a third one as well: the inode change time. This is often referred to
+as a file's @code{ctime}.
+The inode change time represents the time when the file's meta-information
+last changed. One common example of this is when the permissions of a
+file change. Changing the permissions doesn't access the file, so
+the atime doesn't change, nor does it modify the file, so the mtime
+doesn't change. Yet, something about the file itself has changed,
+and this must be noted somewhere. This is the job of the ctime field.
+This is necessary, so that, for example, a backup program can make a
+fresh copy of the file, including the new permissions value.
+Another operation that modifies a file's ctime without affecting
+the others is renaming. In any case, it is not possible, in normal
+operations, for a user to change the ctime field to a user-specified value.
+
+@vindex TZ
+Time stamps assume the time zone rules specified by the @env{TZ}
+environment variable, or by the system default rules if @env{TZ} is
+not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
+libc, The GNU C Library Reference Manual}.
+You can avoid ambiguities during
+daylight saving transitions by using @sc{utc} time stamps.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --time=atime
+@itemx --time=access
+@itemx --time=use
+@opindex -a
+@opindex --time
+@opindex atime@r{, changing}
+@opindex access @r{time, changing}
+@opindex use @r{time, changing}
+Change the access time only.
+
+@item -c
+@itemx --no-create
+@opindex -c
+@opindex --no-create
+Do not create files that do not exist.
+
+@item -d
+@itemx --date=@var{time}
+@opindex -d
+@opindex --date
+@opindex time
+Use @var{time} instead of the current time. It can contain month names,
+time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
+example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
+specifies the instant of time that is 489,392,193 nanoseconds after
+February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
+minutes east of @acronym{UTC}. @xref{Date input formats}.
+File systems that do not support high-resolution time stamps
+silently ignore any excess precision here.
+
+@item -f
+@opindex -f
+@cindex BSD @command{touch} compatibility
+Ignored; for compatibility with BSD versions of @command{touch}.
+
+@item -m
+@itemx --time=mtime
+@itemx --time=modify
+@opindex -m
+@opindex --time
+@opindex mtime@r{, changing}
+@opindex modify @r{time, changing}
+Change the modification time only.
+
+@item -r @var{file}
+@itemx --reference=@var{file}
+@opindex -r
+@opindex --reference
+Use the times of the reference @var{file} instead of the current time.
+If this option is combined with the @option{--date=@var{time}}
+(@option{-d @var{time}}) option, the reference @var{file}'s time is
+the origin for any relative @var{time}s given, but is otherwise ignored.
+For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
+equal to five seconds before the corresponding time stamp for @file{foo}.
+
+@item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
+Use the argument (optional four-digit or two-digit years, months,
+days, hours, minutes, optional seconds) instead of the current time.
+If the year is specified with only two digits, then @var{cc}
+is 20 for years in the range 0 @dots{} 68, and 19 for years in
+69 @dots{} 99. If no digits of the year are specified,
+the argument is interpreted as a date in the current year.
+
+@end table
+
+@vindex _POSIX2_VERSION
+On older systems, @command{touch} supports an obsolete syntax, as follows.
+If no timestamp is given with any of the @option{-d}, @option{-r}, or
+@option{-t} options, and if there are two or more @var{file}s and the
+first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
+would be a valid argument to the @option{-t} option (if the @var{yy}, if
+any, were moved to the front), and if the represented year
+is in the range 1969--1999, that argument is interpreted as the time
+for the other files instead of as a file name.
+This obsolete behavior can be enabled or disabled with the
+@env{_POSIX2_VERSION} environment variable (@pxref{Standards
+conformance}), but portable scripts should avoid commands whose
+behavior depends on this variable.
+For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
+12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
+
+@exitstatus
+
+
+@node Disk usage
+@chapter Disk usage
+
+@cindex disk usage
+
+No disk can hold an infinite amount of data. These commands report
+how much disk storage is in use or available, report other file and
+file status information, and write buffers to disk.
+
+@menu
+* df invocation:: Report file system disk space usage.
+* du invocation:: Estimate file space usage.
+* stat invocation:: Report file or file system status.
+* sync invocation:: Synchronize memory and disk.
+* truncate invocation:: Shrink or extend the size of a file.
+@end menu
+
+
+@node df invocation
+@section @command{df}: Report file system disk space usage
+
+@pindex df
+@cindex file system disk usage
+@cindex disk usage by file system
+
+@command{df} reports the amount of disk space used and available on
+file systems. Synopsis:
+
+@example
+df [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+With no arguments, @command{df} reports the space used and available on all
+currently mounted file systems (of all types). Otherwise, @command{df}
+reports on the file system containing each argument @var{file}.
+
+Normally the disk space is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+Non-integer quantities are rounded up to the next higher unit.
+
+@cindex disk device file
+@cindex device file, disk
+If an argument @var{file} is a disk device file containing a mounted
+file system, @command{df} shows the space available on that file system
+rather than on the file system containing the device node (i.e., the root
+file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
+on unmounted file systems, because on most kinds of systems doing so
+requires extremely nonportable intimate knowledge of file system
+structures.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+@cindex automounter file systems
+@cindex ignore file systems
+Include in the listing dummy file systems, which
+are omitted by default. Such file systems are typically special-purpose
+pseudo-file-systems, such as automounter entries.
+
+@item -B @var{size}
+@itemx --block-size=@var{size}
+@opindex -B
+@opindex --block-size
+@cindex file system sizes
+Scale sizes by @var{size} before printing them (@pxref{Block size}).
+For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
+
+@itemx --total
+@opindex --total
+@cindex grand total of disk size, usage and available space
+Print a grand total of all arguments after all arguments have
+been processed. This can be used to find out the total disk size, usage
+and available space of all listed devices.
+
+@optHumanReadable
+
+@item -H
+@opindex -H
+Equivalent to @option{--si}.
+
+@item -i
+@itemx --inodes
+@opindex -i
+@opindex --inodes
+@cindex inode usage
+List inode usage information instead of block usage. An inode (short
+for index node) contains information about a file such as its owner,
+permissions, timestamps, and location on the disk.
+
+@item -k
+@opindex -k
+@cindex kibibytes for file system sizes
+Print sizes in 1024-byte blocks, overriding the default block size
+(@pxref{Block size}).
+This option is equivalent to @option{--block-size=1K}.
+
+@item -l
+@itemx --local
+@opindex -l
+@opindex --local
+@cindex file system types, limiting output to certain
+Limit the listing to local file systems. By default, remote file systems
+are also listed.
+
+@item --no-sync
+@opindex --no-sync
+@cindex file system space, retrieving old data more quickly
+Do not invoke the @code{sync} system call before getting any usage data.
+This may make @command{df} run significantly faster on systems with many
+disks, but on some systems (notably SunOS) the results may be slightly
+out of date. This is the default.
+
+@item -P
+@itemx --portability
+@opindex -P
+@opindex --portability
+@cindex one-line output format
+@cindex @acronym{POSIX} output format
+@cindex portable output format
+@cindex output format, portable
+Use the @acronym{POSIX} output format. This is like the default format except
+for the following:
+
+@enumerate
+@item
+The information about each file system is always printed on exactly
+one line; a mount device is never put on a line by itself. This means
+that if the mount device name is more than 20 characters long (e.g., for
+some network mounts), the columns are misaligned.
+
+@item
+The labels in the header output line are changed to conform to @acronym{POSIX}.
+
+@item
+The default block size and output format are unaffected by the
+@env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
+variables. However, the default block size is still affected by
+@env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
+otherwise. @xref{Block size}.
+@end enumerate
+
+@optSi
+
+@item --sync
+@opindex --sync
+@cindex file system space, retrieving current data more slowly
+Invoke the @code{sync} system call before getting any usage data. On
+some systems (notably SunOS), doing this yields more up to date results,
+but in general this option makes @command{df} much slower, especially when
+there are many or very busy file systems.
+
+@item -t @var{fstype}
+@itemx --type=@var{fstype}
+@opindex -t
+@opindex --type
+@cindex file system types, limiting output to certain
+Limit the listing to file systems of type @var{fstype}. Multiple
+file system types can be specified by giving multiple @option{-t} options.
+By default, nothing is omitted.
+
+@item -T
+@itemx --print-type
+@opindex -T
+@opindex --print-type
+@cindex file system types, printing
+Print each file system's type. The types printed here are the same ones
+you can include or exclude with @option{-t} and @option{-x}. The particular
+types printed are whatever is supported by the system. Here are some of
+the common names (this list is certainly not exhaustive):
+
+@table @samp
+
+@item nfs
+@cindex @acronym{NFS} file system type
+An @acronym{NFS} file system, i.e., one mounted over a network from another
+machine. This is the one type name which seems to be used uniformly by
+all systems.
+
+@item 4.2@r{, }ufs@r{, }efs@dots{}
+@cindex Linux file system types
+@cindex local file system types
+@opindex 4.2 @r{file system type}
+@opindex ufs @r{file system type}
+@opindex efs @r{file system type}
+A file system on a locally-mounted hard disk. (The system might even
+support more than one type here; Linux does.)
+
+@item hsfs@r{, }cdfs
+@cindex CD-ROM file system type
+@cindex High Sierra file system
+@opindex hsfs @r{file system type}
+@opindex cdfs @r{file system type}
+A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
+systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
+
+@item pcfs
+@cindex PC file system
+@cindex DOS file system
+@cindex MS-DOS file system
+@cindex diskette file system
+@opindex pcfs
+An MS-DOS file system, usually on a diskette.
+
+@end table
+
+@item -x @var{fstype}
+@itemx --exclude-type=@var{fstype}
+@opindex -x
+@opindex --exclude-type
+Limit the listing to file systems not of type @var{fstype}.
+Multiple file system types can be eliminated by giving multiple
+@option{-x} options. By default, no file system types are omitted.
+
+@item -v
+Ignored; for compatibility with System V versions of @command{df}.
+
+@end table
+
+@exitstatus
+Failure includes the case where no output is generated, so you can
+inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
+@var{dir}} to test whether @var{dir} is on a file system of type
+@samp{ext3} or @samp{reiserfs}.
+
+
+@node du invocation
+@section @command{du}: Estimate file space usage
+
+@pindex du
+@cindex file space usage
+@cindex disk usage for files
+
+@command{du} reports the amount of disk space used by the specified files
+and for each subdirectory (of directory arguments). Synopsis:
+
+@example
+du [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+With no arguments, @command{du} reports the disk space for the current
+directory. Normally the disk space is printed in units of
+1024 bytes, but this can be overridden (@pxref{Block size}).
+Non-integer quantities are rounded up to the next higher unit.
+
+If two or more hard links point to the same file, only one of the hard
+links is counted. The @var{file} argument order affects which links
+are counted, and changing the argument order may change the numbers
+that @command{du} outputs.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Show counts for all files, not just directories.
+
+@itemx --apparent-size
+@opindex --apparent-size
+Print apparent sizes, rather than disk usage. The apparent size of a
+file is the number of bytes reported by @code{wc -c} on regular files,
+or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
+For example, a file containing the word @samp{zoo} with no newline would,
+of course, have an apparent size of 3. Such a small file may require
+anywhere from 0 to 16 KiB or more of disk space, depending on
+the type and configuration of the file system on which the file resides.
+However, a sparse file created with this command:
+
+@example
+dd bs=1 seek=2GiB if=/dev/null of=big
+@end example
+
+@noindent
+has an apparent size of 2 GiB, yet on most modern
+systems, it actually uses almost no disk space.
+
+@item -b
+@itemx --bytes
+@opindex -b
+@opindex --bytes
+Equivalent to @code{--apparent-size --block-size=1}.
+
+@item -B @var{size}
+@itemx --block-size=@var{size}
+@opindex -B
+@opindex --block-size
+@cindex file sizes
+Scale sizes by @var{size} before printing them (@pxref{Block size}).
+For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
+
+@item -c
+@itemx --total
+@opindex -c
+@opindex --total
+@cindex grand total of disk space
+Print a grand total of all arguments after all arguments have
+been processed. This can be used to find out the total disk usage of
+a given set of files or directories.
+
+@item -D
+@itemx --dereference-args
+@opindex -D
+@opindex --dereference-args
+Dereference symbolic links that are command line arguments.
+Does not affect other symbolic links. This is helpful for finding
+out the disk usage of directories, such as @file{/usr/tmp}, which
+are often symbolic links.
+
+@c --files0-from=FILE
+@filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
+
+@optHumanReadable
+
+@item -H
+@opindex -H
+Equivalent to @option{--dereference-args} (@option{-D}).
+
+@item -k
+@opindex -k
+@cindex kibibytes for file sizes
+Print sizes in 1024-byte blocks, overriding the default block size
+(@pxref{Block size}).
+This option is equivalent to @option{--block-size=1K}.
+
+@item -l
+@itemx --count-links
+@opindex -l
+@opindex --count-links
+@cindex hard links, counting in @command{du}
+Count the size of all files, even if they have appeared already (as a
+hard link).
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+@cindex symbolic links, dereferencing in @command{du}
+Dereference symbolic links (show the disk space used by the file
+or directory that the link points to instead of the space used by
+the link).
+
+@item -m
+@opindex -m
+@cindex mebibytes for file sizes
+Print sizes in 1,048,576-byte blocks, overriding the default block size
+(@pxref{Block size}).
+This option is equivalent to @option{--block-size=1M}.
+
+@item -P
+@itemx --no-dereference
+@opindex -P
+@opindex --no-dereference
+@cindex symbolic links, dereferencing in @command{du}
+For each symbolic links encountered by @command{du},
+consider the disk space used by the symbolic link.
+
+@item --max-depth=@var{depth}
+@opindex --max-depth=@var{depth}
+@cindex limiting output of @command{du}
+Show the total for each directory (and file if --all) that is at
+most MAX_DEPTH levels down from the root of the hierarchy. The root
+is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
+
+@item -0
+@opindex -0
+@itemx --null
+@opindex --null
+@cindex output null-byte-terminated lines
+Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
+rather than a newline. This option enables other programs to parse the
+output of @command{du} even when that output would contain file names
+with embedded newlines.
+
+@optSi
+
+@item -s
+@itemx --summarize
+@opindex -s
+@opindex --summarize
+Display only a total for each argument.
+
+@item -S
+@itemx --separate-dirs
+@opindex -S
+@opindex --separate-dirs
+Normally, in the output of @command{du} (when not using @option{--summarize}),
+the size listed next to a directory name, @var{d}, represents the sum
+of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
+With @option{--separate-dirs}, the size reported for a directory name,
+@var{d}, is merely the @code{stat.st_size}-derived size of the directory
+entry, @var{d}.
+
+@itemx --time
+@opindex --time
+@cindex last modified dates, displaying in @command{du}
+Show time of the most recent modification of any file in the directory,
+or any of its subdirectories.
+
+@itemx --time=ctime
+@itemx --time=status
+@itemx --time=use
+@opindex --time
+@opindex ctime@r{, show the most recent}
+@opindex status time@r{, show the most recent}
+@opindex use time@r{, show the most recent}
+Show the most recent status change time (the @samp{ctime} in the inode) of
+any file in the directory, instead of the modification time.
+
+@itemx --time=atime
+@itemx --time=access
+@opindex --time
+@opindex atime@r{, show the most recent}
+@opindex access time@r{, show the most recent}
+Show the most recent access time (the @samp{atime} in the inode) of
+any file in the directory, instead of the modification time.
+
+@item --time-style=@var{style}
+@opindex --time-style
+@cindex time style
+List timestamps in style @var{style}. This option has an effect only if
+the @option{--time} option is also specified. The @var{style} should
+be one of the following:
+
+@table @samp
+@item +@var{format}
+@vindex LC_TIME
+List timestamps using @var{format}, where @var{format} is interpreted
+like the format argument of @command{date} (@pxref{date invocation}).
+For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
+@command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
+with @command{date}, @var{format}'s interpretation is affected by the
+@env{LC_TIME} locale category.
+
+@item full-iso
+List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
+format with nanosecond precision, e.g., @samp{2002-03-30
+23:45:56.477817180 -0700}. This style is equivalent to
+@samp{+%Y-%m-%d %H:%M:%S.%N %z}.
+
+@item long-iso
+List @acronym{ISO} 8601 date and time in minutes, e.g.,
+@samp{2002-03-30 23:45}. These timestamps are shorter than
+@samp{full-iso} timestamps, and are usually good enough for everyday
+work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
+
+@item iso
+List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
+This style is equivalent to @samp{+%Y-%m-%d}.
+@end table
+
+@vindex TIME_STYLE
+You can specify the default value of the @option{--time-style} option
+with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
+the default style is @samp{long-iso}. For compatibility with @command{ls},
+if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
+the newline and any later characters are ignored; if @env{TIME_STYLE}
+begins with @samp{posix-} the @samp{posix-} is ignored; and if
+@env{TIME_STYLE} is @samp{locale} it is ignored.
+
+@item -x
+@itemx --one-file-system
+@opindex -x
+@opindex --one-file-system
+@cindex one file system, restricting @command{du} to
+Skip directories that are on different file systems from the one that
+the argument being processed is on.
+
+@item --exclude=@var{pattern}
+@opindex --exclude=@var{pattern}
+@cindex excluding files from @command{du}
+When recursing, skip subdirectories or files matching @var{pattern}.
+For example, @code{du --exclude='*.o'} excludes files whose names
+end in @samp{.o}.
+
+@item -X @var{file}
+@itemx --exclude-from=@var{file}
+@opindex -X @var{file}
+@opindex --exclude-from=@var{file}
+@cindex excluding files from @command{du}
+Like @option{--exclude}, except take the patterns to exclude from @var{file},
+one per line. If @var{file} is @samp{-}, take the patterns from standard
+input.
+
+@end table
+
+@cindex NFS mounts from BSD to HP-UX
+On BSD systems, @command{du} reports sizes that are half the correct
+values for files that are NFS-mounted from HP-UX systems. On HP-UX
+systems, it reports sizes that are twice the correct values for
+files that are NFS-mounted from BSD systems. This is due to a flaw
+in HP-UX; it also affects the HP-UX @command{du} program.
+
+@exitstatus
+
+
+@node stat invocation
+@section @command{stat}: Report file or file system status
+
+@pindex stat
+@cindex file status
+@cindex file system status
+
+@command{stat} displays information about the specified file(s). Synopsis:
+
+@example
+stat [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+With no option, @command{stat} reports all information about the given files.
+But it also can be used to report the information of the file systems the
+given files are located on. If the files are links, @command{stat} can
+also give information about the files the links point to.
+
+@mayConflictWithShellBuiltIn{stat}
+
+@table @samp
+
+@item -L
+@itemx --dereference
+@opindex -L
+@opindex --dereference
+@cindex symbolic links, dereferencing in @command{stat}
+Change how @command{stat} treats symbolic links.
+With this option, @command{stat} acts on the file referenced
+by each symbolic link argument.
+Without it, @command{stat} acts on any symbolic link argument directly.
+
+@item -f
+@itemx --file-system
+@opindex -f
+@opindex --file-system
+@cindex file systems
+Report information about the file systems where the given files are located
+instead of information about the files themselves.
+
+@item -c
+@itemx --format=@var{format}
+@opindex -c
+@opindex --format=@var{format}
+@cindex output format
+Use @var{format} rather than the default format.
+@var{format} is automatically newline-terminated, so
+running a command like the following with two or more @var{file}
+operands produces a line of output for each operand:
+@example
+$ stat --format=%d:%i / /usr
+2050:2
+2057:2
+@end example
+
+@itemx --printf=@var{format}
+@opindex --printf=@var{format}
+@cindex output format
+Use @var{format} rather than the default format.
+Like @option{--format}, but interpret backslash escapes,
+and do not output a mandatory trailing newline.
+If you want a newline, include @samp{\n} in the @var{format}.
+Here's how you would use @option{--printf} to print the device
+and inode numbers of @file{/} and @file{/usr}:
+@example
+$ stat --printf='%d:%i\n' / /usr
+2050:2
+2057:2
+@end example
+
+@item -t
+@itemx --terse
+@opindex -t
+@opindex --terse
+@cindex terse output
+Print the information in terse form, suitable for parsing by other programs.
+
+@end table
+
+The valid @var{format} directives for files with @option{--format} and
+@option{--printf} are:
+
+@itemize @bullet
+@item %a - Access rights in octal
+@item %A - Access rights in human readable form
+@item %b - Number of blocks allocated (see @samp{%B})
+@item %B - The size in bytes of each block reported by @samp{%b}
+@item %d - Device number in decimal
+@item %D - Device number in hex
+@item %f - Raw mode in hex
+@item %F - File type
+@item %g - Group ID of owner
+@item %G - Group name of owner
+@item %h - Number of hard links
+@item %i - Inode number
+@item %n - File name
+@item %N - Quoted file name with dereference if symbolic link
+@item %o - I/O block size
+@item %s - Total size, in bytes
+@item %t - Major device type in hex
+@item %T - Minor device type in hex
+@item %u - User ID of owner
+@item %U - User name of owner
+@item %x - Time of last access
+@item %X - Time of last access as seconds since Epoch
+@item %y - Time of last modification
+@item %Y - Time of last modification as seconds since Epoch
+@item %z - Time of last change
+@item %Z - Time of last change as seconds since Epoch
+@end itemize
+
+When listing file system information (@option{--file-system} (@option{-f})),
+you must use a different set of @var{format} directives:
+
+@itemize @bullet
+@item %a - Free blocks available to non-super-user
+@item %b - Total data blocks in file system
+@item %c - Total file nodes in file system
+@item %d - Free file nodes in file system
+@item %f - Free blocks in file system
+@item %i - File System ID in hex
+@item %l - Maximum length of file names
+@item %n - File name
+@item %s - Block size (for faster transfers)
+@item %S - Fundamental block size (for block counts)
+@item %t - Type in hex
+@item %T - Type in human readable form
+@end itemize
+
+@vindex TZ
+Time stamps are listed according to the time zone rules specified by
+the @env{TZ} environment variable, or by the system default rules if
+@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
+with @env{TZ}, libc, The GNU C Library Reference Manual}.
+
+@exitstatus
+
+
+@node sync invocation
+@section @command{sync}: Synchronize data on disk with memory
+
+@pindex sync
+@cindex synchronize disk and memory
+
+@cindex superblock, writing
+@cindex inodes, written buffered
+@command{sync} writes any data buffered in memory out to disk. This can
+include (but is not limited to) modified superblocks, modified inodes,
+and delayed reads and writes. This must be implemented by the kernel;
+The @command{sync} program does nothing but exercise the @code{sync} system
+call.
+
+@cindex crashes and corruption
+The kernel keeps data in memory to avoid doing (relatively slow) disk
+reads and writes. This improves performance, but if the computer
+crashes, data may be lost or the file system corrupted as a
+result. The @command{sync} command ensures everything in memory
+is written to disk.
+
+Any arguments are ignored, except for a lone @option{--help} or
+@option{--version} (@pxref{Common options}).
+
+@exitstatus
+
+
+@node truncate invocation
+@section @command{truncate}: Shrink or extend the size of a file
+
+@pindex truncate
+@cindex truncating, file sizes
+
+@command{truncate} shrinks or extends the size of each @var{file} to the
+specified size. Synopsis:
+
+@example
+truncate @var{option}@dots{} @var{file}@dots{}
+@end example
+
+@cindex files, creating
+Any @var{file} that does not exist is created.
+
+@cindex sparse files, creating
+@cindex holes, creating files with
+If a @var{file} is larger than the specified size, the extra data is lost.
+If a @var{file} is shorter, it is extended and the extended part (or hole)
+reads as zero bytes.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --no-create
+@opindex -c
+@opindex --no-create
+Do not create files that do not exist.
+
+@item -o
+@itemx --io-blocks
+@opindex -o
+@opindex --io-blocks
+Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
+
+@item -r @var{rfile}
+@itemx --reference=@var{rfile}
+@opindex -r
+@opindex --reference
+Set the size of each @var{file} to the same size as @var{rfile}.
+
+@item -s @var{size}
+@itemx --size=@var{size}
+@opindex -s
+@opindex --size
+Set the size of each @var{file} to this @var{size}.
+@multiplierSuffixesNoBlocks{size}
+
+@var{size} may also be prefixed by one of the following to adjust
+the size of each @var{file} based on their current size:
+@example
+@samp{+} => extend by
+@samp{-} => reduce by
+@samp{<} => at most
+@samp{>} => at least
+@samp{/} => round down to multiple of
+@samp{%} => round up to multiple of
+@end example
+
+@end table
+
+@exitstatus
+
+
+@node Printing text
+@chapter Printing text
+
+@cindex printing text, commands for
+@cindex commands for printing text
+
+This section describes commands that display text strings.
+
+@menu
+* echo invocation:: Print a line of text.
+* printf invocation:: Format and print data.
+* yes invocation:: Print a string until interrupted.
+@end menu
+
+
+@node echo invocation
+@section @command{echo}: Print a line of text
+
+@pindex echo
+@cindex displaying text
+@cindex printing text
+@cindex text, displaying
+@cindex arbitrary text, displaying
+
+@command{echo} writes each given @var{string} to standard output, with a
+space between each and a newline after the last one. Synopsis:
+
+@example
+echo [@var{option}]@dots{} [@var{string}]@dots{}
+@end example
+
+@mayConflictWithShellBuiltIn{echo}
+
+The program accepts the following options. Also see @ref{Common options}.
+Options must precede operands, and the normally-special argument
+@samp{--} has no special meaning and is treated like any other
+@var{string}.
+
+@table @samp
+@item -n
+@opindex -n
+Do not output the trailing newline.
+
+@item -e
+@opindex -e
+@cindex backslash escapes
+Enable interpretation of the following backslash-escaped characters in
+each @var{string}:
+
+@table @samp
+@item \a
+alert (bell)
+@item \b
+backspace
+@item \c
+produce no further output
+@item \f
+form feed
+@item \n
+newline
+@item \r
+carriage return
+@item \t
+horizontal tab
+@item \v
+vertical tab
+@item \\
+backslash
+@item \0@var{nnn}
+the eight-bit value that is the octal number @var{nnn}
+(zero to three octal digits)
+@item \@var{nnn}
+the eight-bit value that is the octal number @var{nnn}
+(one to three octal digits)
+@item \x@var{hh}
+the eight-bit value that is the hexadecimal number @var{hh}
+(one or two hexadecimal digits)
+@end table
+
+@item -E
+@opindex -E
+@cindex backslash escapes
+Disable interpretation of backslash escapes in each @var{string}.
+This is the default. If @option{-e} and @option{-E} are both
+specified, the last one given takes effect.
+
+@end table
+
+@vindex POSIXLY_CORRECT
+If the @env{POSIXLY_CORRECT} environment variable is set, then when
+@command{echo}'s first argument is not @option{-n} it outputs
+option-like arguments instead of treating them as options. For
+example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
+plain @samp{hello}.
+
+@acronym{POSIX} does not require support for any options, and says
+that the behavior of @command{echo} is implementation-defined if any
+@var{string} contains a backslash or if the first argument is
+@option{-n}. Portable programs can use the @command{printf} command
+if they need to omit trailing newlines or output control characters or
+backslashes. @xref{printf invocation}.
+
+@exitstatus
+
+
+@node printf invocation
+@section @command{printf}: Format and print data
+
+@pindex printf
+@command{printf} does formatted printing of text. Synopsis:
+
+@example
+printf @var{format} [@var{argument}]@dots{}
+@end example
+
+@command{printf} prints the @var{format} string, interpreting @samp{%}
+directives and @samp{\} escapes to format numeric and string arguments
+in a way that is mostly similar to the C @samp{printf} function.
+@xref{Output Conversion Syntax,, @command{printf} format directives,
+libc, The GNU C Library Reference Manual}, for details.
+The differences are listed below.
+
+@mayConflictWithShellBuiltIn{printf}
+
+@itemize @bullet
+
+@item
+The @var{format} argument is reused as necessary to convert all the
+given @var{argument}s. For example, the command @samp{printf %s a b}
+outputs @samp{ab}.
+
+@item
+Missing @var{argument}s are treated as null strings or as zeros,
+depending on whether the context expects a string or a number. For
+example, the command @samp{printf %sx%d} prints @samp{x0}.
+
+@item
+@kindex \c
+An additional escape, @samp{\c}, causes @command{printf} to produce no
+further output. For example, the command @samp{printf 'A%sC\cD%sF' B
+E} prints @samp{ABC}.
+
+@item
+The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
+digits, as opposed to C where it can have an unlimited number of
+digits. For example, the command @samp{printf '\x07e'} prints two
+bytes, whereas the C statement @samp{printf ("\x07e")} prints just
+one.
+
+@item
+@kindex %b
+@command{printf} has an additional directive, @samp{%b}, which prints its
+argument string with @samp{\} escapes interpreted in the same way as in
+the @var{format} string, except that octal escapes are of the form
+@samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
+If a precision is also given, it limits the number of bytes printed
+from the converted string.
+
+@item
+Numeric arguments must be single C constants, possibly with leading
+@samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
+@samp{-0003}.
+
+@item
+@vindex POSIXLY_CORRECT
+If the leading character of a numeric argument is @samp{"} or @samp{'}
+then its value is the numeric value of the immediately following
+character. Any remaining characters are silently ignored if the
+@env{POSIXLY_CORRECT} environment variable is set; otherwise, a
+warning is printed. For example, @samp{printf "%d" "'a"} outputs
+@samp{97} on hosts that use the @acronym{ASCII} character set, since
+@samp{a} has the numeric value 97 in @acronym{ASCII}.
+
+@end itemize
+
+@vindex LC_NUMERIC
+A floating-point argument must use a period before any fractional
+digits, but is printed according to the @env{LC_NUMERIC} category of the
+current locale. For example, in a locale whose radix character is a
+comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
+the command @samp{printf %g 3,14} is an error.
+
+@kindex \@var{ooo}
+@kindex \x@var{hh}
+@command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
+(if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
+and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
+digits) specifying a character to print.
+
+@kindex \uhhhh
+@kindex \Uhhhhhhhh
+@cindex Unicode
+@cindex ISO/IEC 10646
+@vindex LC_CTYPE
+@command{printf} interprets two character syntaxes introduced in
+@acronym{ISO} C 99:
+@samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
+characters, specified as
+four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
+characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
+@command{printf} outputs the Unicode characters
+according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
+U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
+for U+0024 ($), U+0040 (@@), and U+0060 (@`).
+
+The processing of @samp{\u} and @samp{\U} requires a full-featured
+@code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
+or when @code{libiconv} is installed prior to this package. Otherwise
+@samp{\u} and @samp{\U} will print as-is.
+
+The only options are a lone @option{--help} or
+@option{--version}. @xref{Common options}.
+Options must precede operands.
+
+The Unicode character syntaxes are useful for writing strings in a locale
+independent way. For example, a string containing the Euro currency symbol
+
+@example
+$ env printf '\u20AC 14.95'
+@end example
+
+@noindent
+will be output correctly in all locales supporting the Euro symbol
+(@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
+
+@example
+$ env printf '\u4e2d\u6587'
+@end example
+
+@noindent
+will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
+
+Note that in these examples, the @command{printf} command has been
+invoked via @command{env} to ensure that we run the program found via
+your shell's search path, and not a shell alias or a built-in function.
+
+For larger strings, you don't need to look up the hexadecimal code
+values of each character one by one. @acronym{ASCII} characters mixed with \u
+escape sequences is also known as the JAVA source file encoding. You can
+use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
+is how to convert a piece of text into a shell script which will output
+this text in a locale-independent way:
+
+@smallexample
+$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
+ '\u4e2d\u6587\n' > sample.txt
+$ recode BIG5..JAVA < sample.txt \
+ | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
+ > sample.sh
+@end smallexample
+
+@exitstatus
+
+
+@node yes invocation
+@section @command{yes}: Print a string until interrupted
+
+@pindex yes
+@cindex repeated output of a string
+
+@command{yes} prints the command line arguments, separated by spaces and
+followed by a newline, forever until it is killed. If no arguments are
+given, it prints @samp{y} followed by a newline forever until killed.
+
+Upon a write error, @command{yes} exits with status @samp{1}.
+
+The only options are a lone @option{--help} or @option{--version}.
+To output an argument that begins with
+@samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
+@xref{Common options}.
+
+
+@node Conditions
+@chapter Conditions
+
+@cindex conditions
+@cindex commands for exit status
+@cindex exit status commands
+
+This section describes commands that are primarily useful for their exit
+status, rather than their output. Thus, they are often used as the
+condition of shell @code{if} statements, or as the last command in a
+pipeline.
+
+@menu
+* false invocation:: Do nothing, unsuccessfully.
+* true invocation:: Do nothing, successfully.
+* test invocation:: Check file types and compare values.
+* expr invocation:: Evaluate expressions.
+@end menu
+
+
+@node false invocation
+@section @command{false}: Do nothing, unsuccessfully
+
+@pindex false
+@cindex do nothing, unsuccessfully
+@cindex failure exit status
+@cindex exit status of @command{false}
+
+@command{false} does nothing except return an exit status of 1, meaning
+@dfn{failure}. It can be used as a place holder in shell scripts
+where an unsuccessful command is needed.
+In most modern shells, @command{false} is a built-in command, so when
+you use @samp{false} in a script, you're probably using the built-in
+command, not the one documented here.
+
+@command{false} honors the @option{--help} and @option{--version} options.
+
+This version of @command{false} is implemented as a C program, and is thus
+more secure and faster than a shell script implementation, and may safely
+be used as a dummy shell for the purpose of disabling accounts.
+
+Note that @command{false} (unlike all other programs documented herein)
+exits unsuccessfully, even when invoked with
+@option{--help} or @option{--version}.
+
+Portable programs should not assume that the exit status of
+@command{false} is 1, as it is greater than 1 on some
+non-@acronym{GNU} hosts.
+
+
+@node true invocation
+@section @command{true}: Do nothing, successfully
+
+@pindex true
+@cindex do nothing, successfully
+@cindex no-op
+@cindex successful exit
+@cindex exit status of @command{true}
+
+@command{true} does nothing except return an exit status of 0, meaning
+@dfn{success}. It can be used as a place holder in shell scripts
+where a successful command is needed, although the shell built-in
+command @code{:} (colon) may do the same thing faster.
+In most modern shells, @command{true} is a built-in command, so when
+you use @samp{true} in a script, you're probably using the built-in
+command, not the one documented here.
+
+@command{true} honors the @option{--help} and @option{--version} options.
+
+Note, however, that it is possible to cause @command{true}
+to exit with nonzero status: with the @option{--help} or @option{--version}
+option, and with standard
+output already closed or redirected to a file that evokes an I/O error.
+For example, using a Bourne-compatible shell:
+
+@example
+$ ./true --version >&-
+./true: write error: Bad file number
+$ ./true --version > /dev/full
+./true: write error: No space left on device
+@end example
+
+This version of @command{true} is implemented as a C program, and is thus
+more secure and faster than a shell script implementation, and may safely
+be used as a dummy shell for the purpose of disabling accounts.
+
+@node test invocation
+@section @command{test}: Check file types and compare values
+
+@pindex test
+@cindex check file types
+@cindex compare values
+@cindex expression evaluation
+
+@command{test} returns a status of 0 (true) or 1 (false) depending on the
+evaluation of the conditional expression @var{expr}. Each part of the
+expression must be a separate argument.
+
+@command{test} has file status checks, string operators, and numeric
+comparison operators.
+
+@command{test} has an alternate form that uses opening and closing
+square brackets instead a leading @samp{test}. For example, instead
+of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
+brackets must be separate arguments; for example, @samp{[-d /]} does
+not have the desired effect. Since @samp{test @var{expr}} and @samp{[
+@var{expr} ]} have the same meaning, only the former form is discussed
+below.
+
+Synopses:
+
+@example
+test @var{expression}
+test
+[ @var{expression} ]
+[ ]
+[ @var{option}
+@end example
+
+@mayConflictWithShellBuiltIn{test}
+
+If @var{expression} is omitted, @command{test} returns false.
+If @var{expression} is a single argument,
+@command{test} returns false if the argument is null and true otherwise. The argument
+can be any string, including strings like @samp{-d}, @samp{-1},
+@samp{--}, @samp{--help}, and @samp{--version} that most other
+programs would treat as options. To get help and version information,
+invoke the commands @samp{[ --help} and @samp{[ --version}, without
+the usual closing brackets. @xref{Common options}.
+
+@cindex exit status of @command{test}
+Exit status:
+
+@display
+0 if the expression is true,
+1 if the expression is false,
+2 if an error occurred.
+@end display
+
+@menu
+* File type tests:: -[bcdfhLpSt]
+* Access permission tests:: -[gkruwxOG]
+* File characteristic tests:: -e -s -nt -ot -ef
+* String tests:: -z -n = !=
+* Numeric tests:: -eq -ne -lt -le -gt -ge
+* Connectives for test:: ! -a -o
+@end menu
+
+
+@node File type tests
+@subsection File type tests
+
+@cindex file type tests
+
+These options test for particular types of files. (Everything's a file,
+but not all files are the same!)
+
+@table @samp
+
+@item -b @var{file}
+@opindex -b
+@cindex block special check
+True if @var{file} exists and is a block special device.
+
+@item -c @var{file}
+@opindex -c
+@cindex character special check
+True if @var{file} exists and is a character special device.
+
+@item -d @var{file}
+@opindex -d
+@cindex directory check
+True if @var{file} exists and is a directory.
+
+@item -f @var{file}
+@opindex -f
+@cindex regular file check
+True if @var{file} exists and is a regular file.
+
+@item -h @var{file}
+@itemx -L @var{file}
+@opindex -L
+@opindex -h
+@cindex symbolic link check
+True if @var{file} exists and is a symbolic link.
+Unlike all other file-related tests, this test does not dereference
+@var{file} if it is a symbolic link.
+
+@item -p @var{file}
+@opindex -p
+@cindex named pipe check
+True if @var{file} exists and is a named pipe.
+
+@item -S @var{file}
+@opindex -S
+@cindex socket check
+True if @var{file} exists and is a socket.
+
+@item -t @var{fd}
+@opindex -t
+@cindex terminal check
+True if @var{fd} is a file descriptor that is associated with a
+terminal.
+
+@end table
+
+
+@node Access permission tests
+@subsection Access permission tests
+
+@cindex access permission tests
+@cindex permission tests
+
+These options test for particular access permissions.
+
+@table @samp
+
+@item -g @var{file}
+@opindex -g
+@cindex set-group-ID check
+True if @var{file} exists and has its set-group-ID bit set.
+
+@item -k @var{file}
+@opindex -k
+@cindex sticky bit check
+True if @var{file} exists and has its @dfn{sticky} bit set.
+
+@item -r @var{file}
+@opindex -r
+@cindex readable file check
+True if @var{file} exists and read permission is granted.
+
+@item -u @var{file}
+@opindex -u
+@cindex set-user-ID check
+True if @var{file} exists and has its set-user-ID bit set.
+
+@item -w @var{file}
+@opindex -w
+@cindex writable file check
+True if @var{file} exists and write permission is granted.
+
+@item -x @var{file}
+@opindex -x
+@cindex executable file check
+True if @var{file} exists and execute permission is granted
+(or search permission, if it is a directory).
+
+@item -O @var{file}
+@opindex -O
+@cindex owned by effective user ID check
+True if @var{file} exists and is owned by the current effective user ID.
+
+@item -G @var{file}
+@opindex -G
+@cindex owned by effective group ID check
+True if @var{file} exists and is owned by the current effective group ID.
+
+@end table
+
+@node File characteristic tests
+@subsection File characteristic tests
+
+@cindex file characteristic tests
+
+These options test other file characteristics.
+
+@table @samp
+
+@item -e @var{file}
+@opindex -e
+@cindex existence-of-file check
+True if @var{file} exists.
+
+@item -s @var{file}
+@opindex -s
+@cindex nonempty file check
+True if @var{file} exists and has a size greater than zero.
+
+@item @var{file1} -nt @var{file2}
+@opindex -nt
+@cindex newer-than file check
+True if @var{file1} is newer (according to modification date) than
+@var{file2}, or if @var{file1} exists and @var{file2} does not.
+
+@item @var{file1} -ot @var{file2}
+@opindex -ot
+@cindex older-than file check
+True if @var{file1} is older (according to modification date) than
+@var{file2}, or if @var{file2} exists and @var{file1} does not.
+
+@item @var{file1} -ef @var{file2}
+@opindex -ef
+@cindex same file check
+@cindex hard link check
+True if @var{file1} and @var{file2} have the same device and inode
+numbers, i.e., if they are hard links to each other.
+
+@end table
+
+
+@node String tests
+@subsection String tests
+
+@cindex string tests
+
+These options test string characteristics. You may need to quote
+@var{string} arguments for the shell. For example:
+
+@example
+test -n "$V"
+@end example
+
+The quotes here prevent the wrong arguments from being passed to
+@command{test} if @samp{$V} is empty or contains special characters.
+
+@table @samp
+
+@item -z @var{string}
+@opindex -z
+@cindex zero-length string check
+True if the length of @var{string} is zero.
+
+@item -n @var{string}
+@itemx @var{string}
+@opindex -n
+@cindex nonzero-length string check
+True if the length of @var{string} is nonzero.
+
+@item @var{string1} = @var{string2}
+@opindex =
+@cindex equal string check
+True if the strings are equal.
+
+@item @var{string1} != @var{string2}
+@opindex !=
+@cindex not-equal string check
+True if the strings are not equal.
+
+@end table
+
+
+@node Numeric tests
+@subsection Numeric tests
+
+@cindex numeric tests
+@cindex arithmetic tests
+
+Numeric relational operators. The arguments must be entirely numeric
+(possibly negative), or the special expression @w{@code{-l @var{string}}},
+which evaluates to the length of @var{string}.
+
+@table @samp
+
+@item @var{arg1} -eq @var{arg2}
+@itemx @var{arg1} -ne @var{arg2}
+@itemx @var{arg1} -lt @var{arg2}
+@itemx @var{arg1} -le @var{arg2}
+@itemx @var{arg1} -gt @var{arg2}
+@itemx @var{arg1} -ge @var{arg2}
+@opindex -eq
+@opindex -ne
+@opindex -lt
+@opindex -le
+@opindex -gt
+@opindex -ge
+These arithmetic binary operators return true if @var{arg1} is equal,
+not-equal, less-than, less-than-or-equal, greater-than, or
+greater-than-or-equal than @var{arg2}, respectively.
+
+@end table
+
+For example:
+
+@example
+test -1 -gt -2 && echo yes
+@result{} yes
+test -l abc -gt 1 && echo yes
+@result{} yes
+test 0x100 -eq 1
+@error{} test: integer expression expected before -eq
+@end example
+
+
+@node Connectives for test
+@subsection Connectives for @command{test}
+
+@cindex logical connectives
+@cindex connectives, logical
+
+The usual logical connectives.
+
+@table @samp
+
+@item ! @var{expr}
+@opindex !
+True if @var{expr} is false.
+
+@item @var{expr1} -a @var{expr2}
+@opindex -a
+@cindex logical and operator
+@cindex and operator
+True if both @var{expr1} and @var{expr2} are true.
+
+@item @var{expr1} -o @var{expr2}
+@opindex -o
+@cindex logical or operator
+@cindex or operator
+True if either @var{expr1} or @var{expr2} is true.
+
+@end table
+
+
+@node expr invocation
+@section @command{expr}: Evaluate expressions
+
+@pindex expr
+@cindex expression evaluation
+@cindex evaluation of expressions
+
+@command{expr} evaluates an expression and writes the result on standard
+output. Each token of the expression must be a separate argument.
+
+Operands are either integers or strings. Integers consist of one or
+more decimal digits, with an optional leading @samp{-}.
+@command{expr} converts
+anything appearing in an operand position to an integer or a string
+depending on the operation being applied to it.
+
+Strings are not quoted for @command{expr} itself, though you may need to
+quote them to protect characters with special meaning to the shell,
+e.g., spaces. However, regardless of whether it is quoted, a string
+operand should not be a parenthesis or any of @command{expr}'s
+operators like @code{+}, so you cannot safely pass an arbitrary string
+@code{$str} to expr merely by quoting it to the shell. One way to
+work around this is to use the @sc{gnu} extension @code{+},
+(e.g., @code{+ "$str" = foo}); a more portable way is to use
+@code{@w{" $str"}} and to adjust the rest of the expression to take
+the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
+
+You should not pass a negative integer or a string with leading
+@samp{-} as @command{expr}'s first argument, as it might be
+misinterpreted as an option; this can be avoided by parenthesization.
+Also, portable scripts should not use a string operand that happens to
+take the form of an integer; this can be worked around by inserting
+leading spaces as mentioned above.
+
+@cindex parentheses for grouping
+Operators may be given as infix symbols or prefix keywords. Parentheses
+may be used for grouping in the usual manner. You must quote
+parentheses and many operators to avoid the shell evaluating them,
+however.
+
+When built with support for the GNU MP library, @command{expr} uses
+arbitrary-precision arithmetic; otherwise, it uses native arithmetic
+types and may fail due to arithmetic overflow.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}. Options must precede operands.
+
+@cindex exit status of @command{expr}
+Exit status:
+
+@display
+0 if the expression is neither null nor 0,
+1 if the expression is null or 0,
+2 if the expression is invalid,
+3 if an internal error occurred (e.g., arithmetic overflow).
+@end display
+
+@menu
+* String expressions:: + : match substr index length
+* Numeric expressions:: + - * / %
+* Relations for expr:: | & < <= = == != >= >
+* Examples of expr:: Examples.
+@end menu
+
+
+@node String expressions
+@subsection String expressions
+
+@cindex string expressions
+@cindex expressions, string
+
+@command{expr} supports pattern matching and other string operators. These
+have higher precedence than both the numeric and relational operators (in
+the next sections).
+
+@table @samp
+
+@item @var{string} : @var{regex}
+@cindex pattern matching
+@cindex regular expression matching
+@cindex matching patterns
+Perform pattern matching. The arguments are converted to strings and the
+second is considered to be a (basic, a la GNU @code{grep}) regular
+expression, with a @code{^} implicitly prepended. The first argument is
+then matched against this regular expression.
+
+If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
+@code{:} expression returns the part of @var{string} that matched the
+subexpression; otherwise, it returns the number of characters matched.
+
+If the match fails, the @code{:} operator returns the null string if
+@samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
+
+@kindex \( @r{regexp operator}
+Only the first @samp{\( @dots{} \)} pair is relevant to the return
+value; additional pairs are meaningful only for grouping the regular
+expression operators.
+
+@kindex \+ @r{regexp operator}
+@kindex \? @r{regexp operator}
+@kindex \| @r{regexp operator}
+In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
+operators which respectively match one or more, zero or one, or separate
+alternatives. SunOS and other @command{expr}'s treat these as regular
+characters. (@acronym{POSIX} allows either behavior.)
+@xref{Top, , Regular Expression Library, regex, Regex}, for details of
+regular expression syntax. Some examples are in @ref{Examples of expr}.
+
+@item match @var{string} @var{regex}
+@findex match
+An alternative way to do pattern matching. This is the same as
+@w{@samp{@var{string} : @var{regex}}}.
+
+@item substr @var{string} @var{position} @var{length}
+@findex substr
+Returns the substring of @var{string} beginning at @var{position}
+with length at most @var{length}. If either @var{position} or
+@var{length} is negative, zero, or non-numeric, returns the null string.
+
+@item index @var{string} @var{charset}
+@findex index
+Returns the first position in @var{string} where the first character in
+@var{charset} was found. If no character in @var{charset} is found in
+@var{string}, return 0.
+
+@item length @var{string}
+@findex length
+Returns the length of @var{string}.
+
+@item + @var{token}
+@kindex +
+Interpret @var{token} as a string, even if it is a keyword like @var{match}
+or an operator like @code{/}.
+This makes it possible to test @code{expr length + "$x"} or
+@code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
+the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
+This operator is a @acronym{GNU} extension. Portable shell scripts should use
+@code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
+
+@end table
+
+To make @command{expr} interpret keywords as strings, you must use the
+@code{quote} operator.
+
+
+@node Numeric expressions
+@subsection Numeric expressions
+
+@cindex numeric expressions
+@cindex expressions, numeric
+
+@command{expr} supports the usual numeric operators, in order of increasing
+precedence. These numeric operators have lower precedence than the
+string operators described in the previous section, and higher precedence
+than the connectives (next section).
+
+@table @samp
+
+@item + -
+@kindex +
+@kindex -
+@cindex addition
+@cindex subtraction
+Addition and subtraction. Both arguments are converted to integers;
+an error occurs if this cannot be done.
+
+@item * / %
+@kindex *
+@kindex /
+@kindex %
+@cindex multiplication
+@cindex division
+@cindex remainder
+Multiplication, division, remainder. Both arguments are converted to
+integers; an error occurs if this cannot be done.
+
+@end table
+
+
+@node Relations for expr
+@subsection Relations for @command{expr}
+
+@cindex connectives, logical
+@cindex logical connectives
+@cindex relations, numeric or string
+
+@command{expr} supports the usual logical connectives and relations. These
+have lower precedence than the string and numeric operators
+(previous sections). Here is the list, lowest-precedence operator first.
+
+@table @samp
+
+@item |
+@kindex |
+@cindex logical or operator
+@cindex or operator
+Returns its first argument if that is neither null nor zero, otherwise
+its second argument if it is neither null nor zero, otherwise 0. It
+does not evaluate its second argument if its first argument is neither
+null nor zero.
+
+@item &
+@kindex &
+@cindex logical and operator
+@cindex and operator
+Return its first argument if neither argument is null or zero, otherwise
+0. It does not evaluate its second argument if its first argument is
+null or zero.
+
+@item < <= = == != >= >
+@kindex <
+@kindex <=
+@kindex =
+@kindex ==
+@kindex >
+@kindex >=
+@cindex comparison operators
+@vindex LC_COLLATE
+Compare the arguments and return 1 if the relation is true, 0 otherwise.
+@code{==} is a synonym for @code{=}. @command{expr} first tries to convert
+both arguments to integers and do a numeric comparison; if either
+conversion fails, it does a lexicographic comparison using the character
+collating sequence specified by the @env{LC_COLLATE} locale.
+
+@end table
+
+
+@node Examples of expr
+@subsection Examples of using @command{expr}
+
+@cindex examples of @command{expr}
+Here are a few examples, including quoting for shell metacharacters.
+
+To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
+
+@example
+foo=`expr $foo + 1`
+@end example
+
+To print the non-directory part of the file name stored in
+@code{$fname}, which need not contain a @code{/}:
+
+@example
+expr $fname : '.*/\(.*\)' '|' $fname
+@end example
+
+An example showing that @code{\+} is an operator:
+
+@example
+expr aaa : 'a\+'
+@result{} 3
+@end example
+
+@example
+expr abc : 'a\(.\)c'
+@result{} b
+expr index abcdef cz
+@result{} 3
+expr index index a
+@error{} expr: syntax error
+expr index + index a
+@result{} 0
+@end example
+
+
+@node Redirection
+@chapter Redirection
+
+@cindex redirection
+@cindex commands for redirection
+
+Unix shells commonly provide several forms of @dfn{redirection}---ways
+to change the input source or output destination of a command. But one
+useful redirection is performed by a separate command, not by the shell;
+it's described here.
+
+@menu
+* tee invocation:: Redirect output to multiple files or processes.
+@end menu
+
+
+@node tee invocation
+@section @command{tee}: Redirect output to multiple files or processes
+
+@pindex tee
+@cindex pipe fitting
+@cindex destinations, multiple output
+@cindex read from stdin and write to stdout and files
+
+The @command{tee} command copies standard input to standard output and also
+to any files given as arguments. This is useful when you want not only
+to send some data down a pipe, but also to save a copy. Synopsis:
+
+@example
+tee [@var{option}]@dots{} [@var{file}]@dots{}
+@end example
+
+If a file being written to does not already exist, it is created. If a
+file being written to already exists, the data it previously contained
+is overwritten unless the @option{-a} option is used.
+
+A @var{file} of @samp{-} causes @command{tee} to send another copy of
+input to standard output, but this is typically not that useful as the
+copies are interleaved.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --append
+@opindex -a
+@opindex --append
+Append standard input to the given files rather than overwriting
+them.
+
+@item -i
+@itemx --ignore-interrupts
+@opindex -i
+@opindex --ignore-interrupts
+Ignore interrupt signals.
+
+@end table
+
+The @command{tee} command is useful when you happen to be transferring a large
+amount of data and also want to summarize that data without reading
+it a second time. For example, when you are downloading a DVD image,
+you often want to verify its signature or checksum right away.
+The inefficient way to do it is simply:
+
+@example
+wget http://example.com/some.iso && sha1sum some.iso
+@end example
+
+One problem with the above is that it makes you wait for the
+download to complete before starting the time-consuming SHA1 computation.
+Perhaps even more importantly, the above requires reading
+the DVD image a second time (the first was from the network).
+
+The efficient way to do it is to interleave the download
+and SHA1 computation. Then, you'll get the checksum for
+free, because the entire process parallelizes so well:
+
+@example
+# slightly contrived, to demonstrate process substitution
+wget -O - http://example.com/dvd.iso \
+ | tee >(sha1sum > dvd.sha1) > dvd.iso
+@end example
+
+That makes @command{tee} write not just to the expected output file,
+but also to a pipe running @command{sha1sum} and saving the final
+checksum in a file named @file{dvd.sha1}.
+
+Note, however, that this example relies on a feature of modern shells
+called @dfn{process substitution}
+(the @samp{>(command)} syntax, above;
+@xref{Process Substitution,,Process Substitution, bashref,
+The Bash Reference Manual}.),
+so it works with @command{zsh}, @command{bash}, and @command{ksh},
+but not with @command{/bin/sh}. So if you write code like this
+in a shell script, be sure to start the script with @samp{#!/bin/bash}.
+
+Since the above example writes to one file and one process,
+a more conventional and portable use of @command{tee} is even better:
+
+@example
+wget -O - http://example.com/dvd.iso \
+ | tee dvd.iso | sha1sum > dvd.sha1
+@end example
+
+You can extend this example to make @command{tee} write to two processes,
+computing MD5 and SHA1 checksums in parallel. In this case,
+process substitution is required:
+
+@example
+wget -O - http://example.com/dvd.iso \
+ | tee >(sha1sum > dvd.sha1) \
+ >(md5sum > dvd.md5) \
+ > dvd.iso
+@end example
+
+This technique is also useful when you want to make a @emph{compressed}
+copy of the contents of a pipe.
+Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
+For a large hierarchy, @samp{du -ak} can run for a long time,
+and can easily produce terabytes of data, so you won't want to
+rerun the command unnecessarily. Nor will you want to save
+the uncompressed output.
+
+Doing it the inefficient way, you can't even start the GUI
+until after you've compressed all of the @command{du} output:
+
+@example
+du -ak | gzip -9 > /tmp/du.gz
+gzip -d /tmp/du.gz | xdiskusage -a
+@end example
+
+With @command{tee} and process substitution, you start the GUI
+right away and eliminate the decompression completely:
+
+@example
+du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
+@end example
+
+Finally, if you regularly create more than one type of
+compressed tarball at once, for example when @code{make dist} creates
+both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
+there may be a better way.
+Typical @command{automake}-generated @file{Makefile} rules create
+the two compressed tar archives with commands in sequence, like this
+(slightly simplified):
+
+@example
+tardir=your-pkg-M.N
+tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
+tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
+@end example
+
+However, if the hierarchy you are archiving and compressing is larger
+than a couple megabytes, and especially if you are using a multi-processor
+system with plenty of memory, then you can do much better by reading the
+directory contents only once and running the compression programs in parallel:
+
+@example
+tardir=your-pkg-M.N
+tar chof - "$tardir" \
+ | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
+ | bzip2 -9 -c > your-pkg-M.N.tar.bz2
+@end example
+
+@exitstatus
+
+
+@node File name manipulation
+@chapter File name manipulation
+
+@cindex file name manipulation
+@cindex manipulation of file names
+@cindex commands for file name manipulation
+
+This section describes commands that manipulate file names.
+
+@menu
+* basename invocation:: Strip directory and suffix from a file name.
+* dirname invocation:: Strip non-directory suffix from a file name.
+* pathchk invocation:: Check file name validity and portability.
+@end menu
+
+
+@node basename invocation
+@section @command{basename}: Strip directory and suffix from a file name
+
+@pindex basename
+@cindex strip directory and suffix from file names
+@cindex directory, stripping from file names
+@cindex suffix, stripping from file names
+@cindex file names, stripping directory and suffix
+@cindex leading directory components, stripping
+
+@command{basename} removes any leading directory components from
+@var{name}. Synopsis:
+
+@example
+basename @var{name} [@var{suffix}]
+@end example
+
+If @var{suffix} is specified and is identical to the end of @var{name},
+it is removed from @var{name} as well. Note that since trailing slashes
+are removed prior to suffix matching, @var{suffix} will do nothing if it
+contains slashes. @command{basename} prints the result on standard
+output.
+
+@c This test is used both here and in the section on dirname.
+@macro basenameAndDirname
+Together, @command{basename} and @command{dirname} are designed such
+that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
+"$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
+for everything except file names containing a trailing newline.
+@end macro
+@basenameAndDirname
+
+@acronym{POSIX} allows the implementation to define the results if
+@var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
+@command{basename} returns the empty string. In the latter case, the
+result is @samp{//} on platforms where @var{//} is distinct from
+@var{/}, and @samp{/} on platforms where there is no difference.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}. Options must precede operands.
+
+@exitstatus
+
+Examples:
+
+@smallexample
+# Output "sort".
+basename /usr/bin/sort
+
+# Output "stdio".
+basename include/stdio.h .h
+@end smallexample
+
+
+@node dirname invocation
+@section @command{dirname}: Strip non-directory suffix from a file name
+
+@pindex dirname
+@cindex directory components, printing
+@cindex stripping non-directory suffix
+@cindex non-directory suffix, stripping
+
+@command{dirname} prints all but the final slash-delimited component of
+a string (presumably a file name). Synopsis:
+
+@example
+dirname @var{name}
+@end example
+
+If @var{name} is a single component, @command{dirname} prints @samp{.}
+(meaning the current directory).
+
+@basenameAndDirname
+
+@acronym{POSIX} allows the implementation to define the results if
+@var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
+result is @samp{//} on platforms where @var{//} is distinct from
+@var{/}, and @samp{/} on platforms where there is no difference.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+Examples:
+
+@smallexample
+# Output "/usr/bin".
+dirname /usr/bin/sort
+
+# Output ".".
+dirname stdio.h
+@end smallexample
+
+
+@node pathchk invocation
+@section @command{pathchk}: Check file name validity and portability
+
+@pindex pathchk
+@cindex file names, checking validity and portability
+@cindex valid file names, checking for
+@cindex portable file names, checking for
+
+@command{pathchk} checks validity and portability of file names. Synopsis:
+
+@example
+pathchk [@var{option}]@dots{} @var{name}@dots{}
+@end example
+
+For each @var{name}, @command{pathchk} prints an error message if any of
+these conditions is true:
+
+@enumerate
+@item
+One of the existing directories in @var{name} does not have search
+(execute) permission,
+@item
+The length of @var{name} is larger than the maximum supported by the
+operating system.
+@item
+The length of one component of @var{name} is longer than
+its file system's maximum.
+@end enumerate
+
+A nonexistent @var{name} is not an error, so long a file with that
+name could be created under the above conditions.
+
+The program accepts the following options. Also see @ref{Common options}.
+Options must precede operands.
+
+@table @samp
+
+@item -p
+@opindex -p
+Instead of performing checks based on the underlying file system,
+print an error message if any of these conditions is true:
+
+@enumerate
+@item
+A file name is empty.
+
+@item
+A file name contains a character outside the @acronym{POSIX} portable file
+name character set, namely, the ASCII letters and digits, @samp{.},
+@samp{_}, @samp{-}, and @samp{/}.
+
+@item
+The length of a file name or one of its components exceeds the
+@acronym{POSIX} minimum limits for portability.
+@end enumerate
+
+@item -P
+@opindex -P
+Print an error message if a file name is empty, or if it contains a component
+that begins with @samp{-}.
+
+@item --portability
+@opindex --portability
+Print an error message if a file name is not portable to all @acronym{POSIX}
+hosts. This option is equivalent to @samp{-p -P}.
+
+@end table
+
+@cindex exit status of @command{pathchk}
+Exit status:
+
+@display
+0 if all specified file names passed all checks,
+1 otherwise.
+@end display
+
+
+@node Working context
+@chapter Working context
+
+@cindex working context
+@cindex commands for printing the working context
+
+This section describes commands that display or alter the context in
+which you are working: the current directory, the terminal settings, and
+so forth. See also the user-related commands in the next section.
+
+@menu
+* pwd invocation:: Print working directory.
+* stty invocation:: Print or change terminal characteristics.
+* printenv invocation:: Print environment variables.
+* tty invocation:: Print file name of terminal on standard input.
+@end menu
+
+
+@node pwd invocation
+@section @command{pwd}: Print working directory
+
+@pindex pwd
+@cindex print name of current directory
+@cindex current working directory, printing
+@cindex working directory, printing
+
+
+@command{pwd} prints the name of the current directory. Synopsis:
+
+@example
+pwd [@var{option}]@dots{}
+@end example
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -L
+@itemx --logical
+@opindex -L
+@opindex --logical
+If the contents of the environment variable @env{PWD} provide an
+absolute name of the current directory with no @samp{.} or @samp{..}
+components, but possibly with symbolic links, then output those
+contents. Otherwise, fall back to default @option{-P} handling.
+
+@item -P
+@itemx --physical
+@opindex -P
+@opindex --physical
+Print a fully resolved name for the current directory. That is, all
+components of the printed name will be actual directory names---none
+will be symbolic links.
+@end table
+
+@cindex symbolic links and @command{pwd}
+If @option{-L} and @option{-P} are both given, the last one takes
+precedence. If neither option is given, then this implementation uses
+@option{-P} as the default unless the @env{POSIXLY_CORRECT}
+environment variable is set.
+
+@mayConflictWithShellBuiltIn{pwd}
+
+@exitstatus
+
+
+@node stty invocation
+@section @command{stty}: Print or change terminal characteristics
+
+@pindex stty
+@cindex change or print terminal settings
+@cindex terminal settings
+@cindex line settings of terminal
+
+@command{stty} prints or changes terminal characteristics, such as baud rate.
+Synopses:
+
+@example
+stty [@var{option}] [@var{setting}]@dots{}
+stty [@var{option}]
+@end example
+
+If given no line settings, @command{stty} prints the baud rate, line
+discipline number (on systems that support it), and line settings
+that have been changed from the values set by @samp{stty sane}.
+By default, mode reading and setting are performed on the tty line
+connected to standard input, although this can be modified by the
+@option{--file} option.
+
+@command{stty} accepts many non-option arguments that change aspects of
+the terminal line operation, as described below.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Print all current settings in human-readable form. This option may not
+be used in combination with any line settings.
+
+@item -F @var{device}
+@itemx --file=@var{device}
+@opindex -F
+@opindex --file
+Set the line opened by the file name specified in @var{device} instead of
+the tty line connected to standard input. This option is necessary
+because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
+prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
+the @code{clocal} flag is not set. Hence, it is not always possible
+to allow the shell to open the device in the traditional manner.
+
+@item -g
+@itemx --save
+@opindex -g
+@opindex --save
+@cindex machine-readable @command{stty} output
+Print all current settings in a form that can be used as an argument to
+another @command{stty} command to restore the current settings. This option
+may not be used in combination with any line settings.
+
+@end table
+
+Many settings can be turned off by preceding them with a @samp{-}.
+Such arguments are marked below with ``May be negated'' in their
+description. The descriptions themselves refer to the positive
+case, that is, when @emph{not} negated (unless stated otherwise,
+of course).
+
+Some settings are not available on all @acronym{POSIX} systems, since they use
+extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
+description. On non-@acronym{POSIX} systems, those or other settings also may not
+be available, but it's not feasible to document all the variations: just
+try it and see.
+
+@exitstatus
+
+@menu
+* Control:: Control settings
+* Input:: Input settings
+* Output:: Output settings
+* Local:: Local settings
+* Combination:: Combination settings
+* Characters:: Special characters
+* Special:: Special settings
+@end menu
+
+
+@node Control
+@subsection Control settings
+
+@cindex control settings
+Control settings:
+
+@table @samp
+@item parenb
+@opindex parenb
+@cindex two-way parity
+Generate parity bit in output and expect parity bit in input.
+May be negated.
+
+@item parodd
+@opindex parodd
+@cindex odd parity
+@cindex even parity
+Set odd parity (even if negated). May be negated.
+
+@item cs5
+@itemx cs6
+@itemx cs7
+@itemx cs8
+@opindex cs@var{n}
+@cindex character size
+@cindex eight-bit characters
+Set character size to 5, 6, 7, or 8 bits.
+
+@item hup
+@itemx hupcl
+@opindex hup[cl]
+Send a hangup signal when the last process closes the tty. May be
+negated.
+
+@item cstopb
+@opindex cstopb
+@cindex stop bits
+Use two stop bits per character (one if negated). May be negated.
+
+@item cread
+@opindex cread
+Allow input to be received. May be negated.
+
+@item clocal
+@opindex clocal
+@cindex modem control
+Disable modem control signals. May be negated.
+
+@item crtscts
+@opindex crtscts
+@cindex hardware flow control
+@cindex flow control, hardware
+@cindex RTS/CTS flow control
+Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
+@end table
+
+
+@node Input
+@subsection Input settings
+
+@cindex input settings
+These settings control operations on data received from the terminal.
+
+@table @samp
+@item ignbrk
+@opindex ignbrk
+@cindex breaks, ignoring
+Ignore break characters. May be negated.
+
+@item brkint
+@opindex brkint
+@cindex breaks, cause interrupts
+Make breaks cause an interrupt signal. May be negated.
+
+@item ignpar
+@opindex ignpar
+@cindex parity, ignoring
+Ignore characters with parity errors. May be negated.
+
+@item parmrk
+@opindex parmrk
+@cindex parity errors, marking
+Mark parity errors (with a 255-0-character sequence). May be negated.
+
+@item inpck
+@opindex inpck
+Enable input parity checking. May be negated.
+
+@item istrip
+@opindex istrip
+@cindex eight-bit input
+Clear high (8th) bit of input characters. May be negated.
+
+@item inlcr
+@opindex inlcr
+@cindex newline, translating to return
+Translate newline to carriage return. May be negated.
+
+@item igncr
+@opindex igncr
+@cindex return, ignoring
+Ignore carriage return. May be negated.
+
+@item icrnl
+@opindex icrnl
+@cindex return, translating to newline
+Translate carriage return to newline. May be negated.
+
+@item iutf8
+@opindex iutf8
+@cindex input encoding, UTF-8
+Assume input characters are UTF-8 encoded. May be negated.
+
+@item ixon
+@opindex ixon
+@kindex C-s/C-q flow control
+@cindex XON/XOFF flow control
+Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
+be negated.
+
+@item ixoff
+@itemx tandem
+@opindex ixoff
+@opindex tandem
+@cindex software flow control
+@cindex flow control, software
+Enable sending of @code{stop} character when the system input buffer
+is almost full, and @code{start} character when it becomes almost
+empty again. May be negated.
+
+@item iuclc
+@opindex iuclc
+@cindex uppercase, translating to lowercase
+Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
+negated. Note ilcuc is not implemented, as one would not be able to issue
+almost any (lowercase) Unix command, after invoking it.
+
+@item ixany
+@opindex ixany
+Allow any character to restart output (only the start character
+if negated). Non-@acronym{POSIX}. May be negated.
+
+@item imaxbel
+@opindex imaxbel
+@cindex beeping at input buffer full
+Enable beeping and not flushing input buffer if a character arrives
+when the input buffer is full. Non-@acronym{POSIX}. May be negated.
+@end table
+
+
+@node Output
+@subsection Output settings
+
+@cindex output settings
+These settings control operations on data sent to the terminal.
+
+@table @samp
+@item opost
+@opindex opost
+Postprocess output. May be negated.
+
+@item olcuc
+@opindex olcuc
+@cindex lowercase, translating to output
+Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
+negated. (Note ouclc is not currently implemented.)
+
+@item ocrnl
+@opindex ocrnl
+@cindex return, translating to newline
+Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
+
+@item onlcr
+@opindex onlcr
+@cindex newline, translating to crlf
+Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
+negated.
+
+@item onocr
+@opindex onocr
+Do not print carriage returns in the first column. Non-@acronym{POSIX}.
+May be negated.
+
+@item onlret
+@opindex onlret
+Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
+
+@item ofill
+@opindex ofill
+@cindex pad instead of timing for delaying
+Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
+May be negated.
+
+@item ofdel
+@opindex ofdel
+@cindex pad character
+Use @acronym{ASCII} @sc{del} characters for fill instead of
+@acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
+May be negated.
+
+@item nl1
+@itemx nl0
+@opindex nl@var{n}
+Newline delay style. Non-@acronym{POSIX}.
+
+@item cr3
+@itemx cr2
+@itemx cr1
+@itemx cr0
+@opindex cr@var{n}
+Carriage return delay style. Non-@acronym{POSIX}.
+
+@item tab3
+@itemx tab2
+@itemx tab1
+@itemx tab0
+@opindex tab@var{n}
+Horizontal tab delay style. Non-@acronym{POSIX}.
+
+@item bs1
+@itemx bs0
+@opindex bs@var{n}
+Backspace delay style. Non-@acronym{POSIX}.
+
+@item vt1
+@itemx vt0
+@opindex vt@var{n}
+Vertical tab delay style. Non-@acronym{POSIX}.
+
+@item ff1
+@itemx ff0
+@opindex ff@var{n}
+Form feed delay style. Non-@acronym{POSIX}.
+@end table
+
+
+@node Local
+@subsection Local settings
+
+@cindex local settings
+
+@table @samp
+@item isig
+@opindex isig
+Enable @code{interrupt}, @code{quit}, and @code{suspend} special
+characters. May be negated.
+
+@item icanon
+@opindex icanon
+Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
+special characters. May be negated.
+
+@item iexten
+@opindex iexten
+Enable non-@acronym{POSIX} special characters. May be negated.
+
+@item echo
+@opindex echo
+Echo input characters. May be negated.
+
+@item echoe
+@itemx crterase
+@opindex echoe
+@opindex crterase
+Echo @code{erase} characters as backspace-space-backspace. May be
+negated.
+
+@item echok
+@opindex echok
+@cindex newline echoing after @code{kill}
+Echo a newline after a @code{kill} character. May be negated.
+
+@item echonl
+@opindex echonl
+@cindex newline, echoing
+Echo newline even if not echoing other characters. May be negated.
+
+@item noflsh
+@opindex noflsh
+@cindex flushing, disabling
+Disable flushing after @code{interrupt} and @code{quit} special
+characters. May be negated.
+
+@item xcase
+@opindex xcase
+@cindex case translation
+Enable input and output of uppercase characters by preceding their
+lowercase equivalents with @samp{\}, when @code{icanon} is set.
+Non-@acronym{POSIX}. May be negated.
+
+@item tostop
+@opindex tostop
+@cindex background jobs, stopping at terminal write
+Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
+May be negated.
+
+@item echoprt
+@itemx prterase
+@opindex echoprt
+@opindex prterase
+Echo erased characters backward, between @samp{\} and @samp{/}.
+Non-@acronym{POSIX}. May be negated.
+
+@item echoctl
+@itemx ctlecho
+@opindex echoctl
+@opindex ctlecho
+@cindex control characters, using @samp{^@var{c}}
+@cindex hat notation for control characters
+Echo control characters in hat notation (@samp{^@var{c}}) instead
+of literally. Non-@acronym{POSIX}. May be negated.
+
+@item echoke
+@itemx crtkill
+@opindex echoke
+@opindex crtkill
+Echo the @code{kill} special character by erasing each character on
+the line as indicated by the @code{echoprt} and @code{echoe} settings,
+instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
+May be negated.
+@end table
+
+
+@node Combination
+@subsection Combination settings
+
+@cindex combination settings
+Combination settings:
+
+@table @samp
+@item evenp
+@opindex evenp
+@itemx parity
+@opindex parity
+Same as @code{parenb -parodd cs7}. May be negated. If negated, same
+as @code{-parenb cs8}.
+
+@item oddp
+@opindex oddp
+Same as @code{parenb parodd cs7}. May be negated. If negated, same
+as @code{-parenb cs8}.
+
+@item nl
+@opindex nl
+Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
+@code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
+
+@item ek
+@opindex ek
+Reset the @code{erase} and @code{kill} special characters to their default
+values.
+
+@item sane
+@opindex sane
+Same as:
+
+@c This is too long to write inline.
+@example
+cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
+-iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
+-onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
+ff0 isig icanon iexten echo echoe echok -echonl
+-noflsh -xcase -tostop -echoprt echoctl echoke
+@end example
+
+@noindent
+and also sets all special characters to their default values.
+
+@item cooked
+@opindex cooked
+Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
+sets the @code{eof} and @code{eol} characters to their default values
+if they are the same as the @code{min} and @code{time} characters.
+May be negated. If negated, same as @code{raw}.
+
+@item raw
+@opindex raw
+Same as:
+
+@example
+-ignbrk -brkint -ignpar -parmrk -inpck -istrip
+-inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
+-imaxbel -opost -isig -icanon -xcase min 1 time 0
+@end example
+
+@noindent
+May be negated. If negated, same as @code{cooked}.
+
+@item cbreak
+@opindex cbreak
+Same as @option{-icanon}. May be negated. If negated, same as
+@code{icanon}.
+
+@item pass8
+@opindex pass8
+@cindex eight-bit characters
+Same as @code{-parenb -istrip cs8}. May be negated. If negated,
+same as @code{parenb istrip cs7}.
+
+@item litout
+@opindex litout
+Same as @option{-parenb -istrip -opost cs8}. May be negated.
+If negated, same as @code{parenb istrip opost cs7}.
+
+@item decctlq
+@opindex decctlq
+Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
+
+@item tabs
+@opindex tabs
+Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
+as @code{tab3}.
+
+@item lcase
+@itemx LCASE
+@opindex lcase
+@opindex LCASE
+Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
+(Used for terminals with uppercase characters only.)
+
+@item crt
+@opindex crt
+Same as @code{echoe echoctl echoke}.
+
+@item dec
+@opindex dec
+Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
+@end table
+
+
+@node Characters
+@subsection Special characters
+
+@cindex special characters
+@cindex characters, special
+
+The special characters' default values vary from system to system.
+They are set with the syntax @samp{name value}, where the names are
+listed below and the value can be given either literally, in hat
+notation (@samp{^@var{c}}), or as an integer which may start with
+@samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
+any other digit to indicate decimal.
+
+@cindex disabling special characters
+@kindex u@r{, and disabling special characters}
+For GNU stty, giving a value of @code{^-} or @code{undef} disables that
+special character. (This is incompatible with Ultrix @command{stty},
+which uses a value of @samp{u} to disable a special character. GNU
+@command{stty} treats a value @samp{u} like any other, namely to set that
+special character to @key{U}.)
+
+@table @samp
+
+@item intr
+@opindex intr
+Send an interrupt signal.
+
+@item quit
+@opindex quit
+Send a quit signal.
+
+@item erase
+@opindex erase
+Erase the last character typed.
+
+@item kill
+@opindex kill
+Erase the current line.
+
+@item eof
+@opindex eof
+Send an end of file (terminate the input).
+
+@item eol
+@opindex eol
+End the line.
+
+@item eol2
+@opindex eol2
+Alternate character to end the line. Non-@acronym{POSIX}.
+
+@item swtch
+@opindex swtch
+Switch to a different shell layer. Non-@acronym{POSIX}.
+
+@item start
+@opindex start
+Restart the output after stopping it.
+
+@item stop
+@opindex stop
+Stop the output.
+
+@item susp
+@opindex susp
+Send a terminal stop signal.
+
+@item dsusp
+@opindex dsusp
+Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
+
+@item rprnt
+@opindex rprnt
+Redraw the current line. Non-@acronym{POSIX}.
+
+@item werase
+@opindex werase
+Erase the last word typed. Non-@acronym{POSIX}.
+
+@item lnext
+@opindex lnext
+Enter the next character typed literally, even if it is a special
+character. Non-@acronym{POSIX}.
+@end table
+
+
+@node Special
+@subsection Special settings
+
+@cindex special settings
+
+@table @samp
+@item min @var{n}
+@opindex min
+Set the minimum number of characters that will satisfy a read until
+the time value has expired, when @option{-icanon} is set.
+
+@item time @var{n}
+@opindex time
+Set the number of tenths of a second before reads time out if the minimum
+number of characters have not been read, when @option{-icanon} is set.
+
+@item ispeed @var{n}
+@opindex ispeed
+Set the input speed to @var{n}.
+
+@item ospeed @var{n}
+@opindex ospeed
+Set the output speed to @var{n}.
+
+@item rows @var{n}
+@opindex rows
+Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
+
+@item cols @var{n}
+@itemx columns @var{n}
+@opindex cols
+@opindex columns
+Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
+
+@item size
+@opindex size
+@vindex LINES
+@vindex COLUMNS
+Print the number of rows and columns that the kernel thinks the
+terminal has. (Systems that don't support rows and columns in the kernel
+typically use the environment variables @env{LINES} and @env{COLUMNS}
+instead; however, GNU @command{stty} does not know anything about them.)
+Non-@acronym{POSIX}.
+
+@item line @var{n}
+@opindex line
+Use line discipline @var{n}. Non-@acronym{POSIX}.
+
+@item speed
+@opindex speed
+Print the terminal speed.
+
+@item @var{n}
+@cindex baud rate, setting
+Set the input and output speeds to @var{n}. @var{n} can be one of: 0
+50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
+38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
+@code{extb} is the same as 38400. Many systems, including GNU/Linux,
+support higher speeds. The @command{stty} command includes support
+for speeds of
+57600,
+115200,
+230400,
+460800,
+500000,
+576000,
+921600,
+1000000,
+1152000,
+1500000,
+2000000,
+2500000,
+3000000,
+3500000,
+or
+4000000 where the system supports these.
+0 hangs up the line if @option{-clocal} is set.
+@end table
+
+
+@node printenv invocation
+@section @command{printenv}: Print all or some environment variables
+
+@pindex printenv
+@cindex printing all or some environment variables
+@cindex environment variables, printing
+
+@command{printenv} prints environment variable values. Synopsis:
+
+@example
+printenv [@var{option}] [@var{variable}]@dots{}
+@end example
+
+If no @var{variable}s are specified, @command{printenv} prints the value of
+every environment variable. Otherwise, it prints the value of each
+@var{variable} that is set, and nothing for those that are not set.
+
+The only options are a lone @option{--help} or @option{--version}.
+@xref{Common options}.
+
+@cindex exit status of @command{printenv}
+Exit status:
+
+@display
+0 if all variables specified were found
+1 if at least one specified variable was not found
+2 if a write error occurred
+@end display
+
+
+@node tty invocation
+@section @command{tty}: Print file name of terminal on standard input
+
+@pindex tty
+@cindex print terminal file name
+@cindex terminal file name, printing
+
+@command{tty} prints the file name of the terminal connected to its standard
+input. It prints @samp{not a tty} if standard input is not a terminal.
+Synopsis:
+
+@example
+tty [@var{option}]@dots{}
+@end example
+
+The program accepts the following option. Also see @ref{Common options}.
+
+@table @samp
+
+@item -s
+@itemx --silent
+@itemx --quiet
+@opindex -s
+@opindex --silent
+@opindex --quiet
+Print nothing; only return an exit status.
+
+@end table
+
+@cindex exit status of @command{tty}
+Exit status:
+
+@display
+0 if standard input is a terminal
+1 if standard input is not a terminal
+2 if given incorrect arguments
+3 if a write error occurs
+@end display
+
+
+@node User information
+@chapter User information
+
+@cindex user information, commands for
+@cindex commands for printing user information
+
+This section describes commands that print user-related information:
+logins, groups, and so forth.
+
+@menu
+* id invocation:: Print user identity.
+* logname invocation:: Print current login name.
+* whoami invocation:: Print effective user ID.
+* groups invocation:: Print group names a user is in.
+* users invocation:: Print login names of users currently logged in.
+* who invocation:: Print who is currently logged in.
+@end menu
+
+
+@node id invocation
+@section @command{id}: Print user identity
+
+@pindex id
+@cindex real user and group IDs, printing
+@cindex effective user and group IDs, printing
+@cindex printing real and effective user and group IDs
+
+@command{id} prints information about the given user, or the process
+running it if no user is specified. Synopsis:
+
+@example
+id [@var{option}]@dots{} [@var{username}]
+@end example
+
+By default, it prints the real user ID, real group ID, effective user ID
+if different from the real user ID, effective group ID if different from
+the real group ID, and supplemental group IDs.
+
+Each of these numeric values is preceded by an identifying string and
+followed by the corresponding user or group name in parentheses.
+
+The options cause @command{id} to print only part of the above information.
+Also see @ref{Common options}.
+
+@table @samp
+@item -g
+@itemx --group
+@opindex -g
+@opindex --group
+Print only the group ID.
+
+@item -G
+@itemx --groups
+@opindex -G
+@opindex --groups
+Print only the group ID and the supplementary groups.
+
+@item -n
+@itemx --name
+@opindex -n
+@opindex --name
+Print the user or group name instead of the ID number. Requires
+@option{-u}, @option{-g}, or @option{-G}.
+
+@item -r
+@itemx --real
+@opindex -r
+@opindex --real
+Print the real, instead of effective, user or group ID. Requires
+@option{-u}, @option{-g}, or @option{-G}.
+
+@item -u
+@itemx --user
+@opindex -u
+@opindex --user
+Print only the user ID.
+
+@end table
+
+@exitstatus
+
+@macro primaryAndSupplementaryGroups{cmd,arg}
+Primary and supplementary groups for a process are normally inherited
+from its parent and are usually unchanged since login. This means
+that if you change the group database after logging in, @command{\cmd\}
+will not reflect your changes within your existing login session.
+Running @command{\cmd\} with a \arg\ causes the user and group
+database to be consulted afresh, and so will give a different result.
+@end macro
+@primaryAndSupplementaryGroups{id,user argument}
+
+@node logname invocation
+@section @command{logname}: Print current login name
+
+@pindex logname
+@cindex printing user's login name
+@cindex login name, printing
+@cindex user name, printing
+
+@flindex utmp
+@command{logname} prints the calling user's name, as found in a
+system-maintained file (often @file{/var/run/utmp} or
+@file{/etc/utmp}), and exits with a status of 0. If there is no entry
+for the calling process, @command{logname} prints
+an error message and exits with a status of 1.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node whoami invocation
+@section @command{whoami}: Print effective user ID
+
+@pindex whoami
+@cindex effective user ID, printing
+@cindex printing the effective user ID
+
+@command{whoami} prints the user name associated with the current
+effective user ID. It is equivalent to the command @samp{id -un}.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node groups invocation
+@section @command{groups}: Print group names a user is in
+
+@pindex groups
+@cindex printing groups a user is in
+@cindex supplementary groups, printing
+
+@command{groups} prints the names of the primary and any supplementary
+groups for each given @var{username}, or the current process if no names
+are given. If more than one name is given, the name of each user is
+printed before
+the list of that user's groups and the user name is separated from the
+group list by a colon. Synopsis:
+
+@example
+groups [@var{username}]@dots{}
+@end example
+
+The group lists are equivalent to the output of the command @samp{id -Gn}.
+
+@primaryAndSupplementaryGroups{groups,list of users}
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node users invocation
+@section @command{users}: Print login names of users currently logged in
+
+@pindex users
+@cindex printing current usernames
+@cindex usernames, printing current
+
+@cindex login sessions, printing users with
+@command{users} prints on a single line a blank-separated list of user
+names of users currently logged in to the current host. Each user name
+corresponds to a login session, so if a user has more than one login
+session, that user's name will appear the same number of times in the
+output. Synopsis:
+
+@example
+users [@var{file}]
+@end example
+
+@flindex utmp
+@flindex wtmp
+With no @var{file} argument, @command{users} extracts its information from
+a system-maintained file (often @file{/var/run/utmp} or
+@file{/etc/utmp}). If a file argument is given, @command{users} uses
+that file instead. A common choice is @file{/var/log/wtmp}.
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node who invocation
+@section @command{who}: Print who is currently logged in
+
+@pindex who
+@cindex printing current user information
+@cindex information, about current users
+
+@command{who} prints information about users who are currently logged on.
+Synopsis:
+
+@example
+@command{who} [@var{option}] [@var{file}] [am i]
+@end example
+
+@cindex terminal lines, currently used
+@cindex login time
+@cindex remote hostname
+If given no non-option arguments, @command{who} prints the following
+information for each user currently logged on: login name, terminal
+line, login time, and remote hostname or X display.
+
+@flindex utmp
+@flindex wtmp
+If given one non-option argument, @command{who} uses that instead of
+a default system-maintained file (often @file{/var/run/utmp} or
+@file{/etc/utmp}) as the name of the file containing the record of
+users logged on. @file{/var/log/wtmp} is commonly given as an argument
+to @command{who} to look at who has previously logged on.
+
+@opindex am i
+@opindex who am i
+If given two non-option arguments, @command{who} prints only the entry
+for the user running it (determined from its standard input), preceded
+by the hostname. Traditionally, the two arguments given are @samp{am
+i}, as in @samp{who am i}.
+
+@vindex TZ
+Time stamps are listed according to the time zone rules specified by
+the @env{TZ} environment variable, or by the system default rules if
+@env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
+with @env{TZ}, libc, The GNU C Library Reference Manual}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Same as @samp{-b -d --login -p -r -t -T -u}.
+
+@item -b
+@itemx --boot
+@opindex -b
+@opindex --boot
+Print the date and time of last system boot.
+
+@item -d
+@itemx --dead
+@opindex -d
+@opindex --dead
+Print information corresponding to dead processes.
+
+@item -H
+@itemx --heading
+@opindex -H
+@opindex --heading
+Print a line of column headings.
+
+@item -l
+@itemx --login
+@opindex -l
+@opindex --login
+List only the entries that correspond to processes via which the
+system is waiting for a user to login. The user name is always @samp{LOGIN}.
+
+@itemx --lookup
+@opindex --lookup
+Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
+is not the default because it can cause significant delays on systems with
+automatic dial-up internet access.
+
+@item -m
+@opindex -m
+Same as @samp{who am i}.
+
+@item -p
+@itemx --process
+@opindex -p
+@opindex --process
+List active processes spawned by init.
+
+@item -q
+@itemx --count
+@opindex -q
+@opindex --count
+Print only the login names and the number of users logged on.
+Overrides all other options.
+
+@item -r
+@itemx --runlevel
+@opindex -r
+@opindex --runlevel
+Print the current (and maybe previous) run-level of the init process.
+
+@item -s
+@opindex -s
+Ignored; for compatibility with other versions of @command{who}.
+
+@item -t
+@itemx --time
+@opindex -t
+@opindex --time
+Print last system clock change.
+
+@itemx -u
+@opindex -u
+@cindex idle time
+After the login time, print the number of hours and minutes that the
+user has been idle. @samp{.} means the user was active in the last minute.
+@samp{old} means the user has been idle for more than 24 hours.
+
+@item -w
+@itemx -T
+@itemx --mesg
+@itemx --message
+@itemx --writable
+@opindex -w
+@opindex -T
+@opindex --mesg
+@opindex --message
+@opindex --writable
+@cindex message status
+@pindex write@r{, allowed}
+After each login name print a character indicating the user's message status:
+
+@display
+@samp{+} allowing @code{write} messages
+@samp{-} disallowing @code{write} messages
+@samp{?} cannot find terminal device
+@end display
+
+@end table
+
+@exitstatus
+
+
+@node System context
+@chapter System context
+
+@cindex system context
+@cindex context, system
+@cindex commands for system context
+
+This section describes commands that print or change system-wide
+information.
+
+@menu
+* arch invocation:: Print machine hardware name.
+* date invocation:: Print or set system date and time.
+* uname invocation:: Print system information.
+* hostname invocation:: Print or set system name.
+* hostid invocation:: Print numeric host identifier.
+* uptime invocation:: Print system uptime and load
+@end menu
+
+@node SELinux context
+@chapter SELinux context
+
+@cindex SELinux context
+@cindex SELinux, context
+@cindex commands for SELinux context
+
+This section describes commands for operations with SELinux
+contexts.
+
+@menu
+* chcon invocation:: Change SELinux context of file
+* runcon invocation:: Run a command in specified SELinux context
+@end menu
+
+@node chcon invocation
+@section @command{chcon}: Change SELinux context of file.
+
+@pindex chcon
+@cindex changing security context
+@cindex change SELinux context
+
+@command{chcon} changes the SELinux security context of the selected files.
+Synopses:
+
+@smallexample
+chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
+chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
+chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
+@end smallexample
+
+Change the SELinux security context of each @var{file} to @var{context}.
+With @option{--reference}, change the security context of each @var{file}
+to that of @var{rfile}.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -h
+@itemx --no-dereference
+@opindex -h
+@opindex --no-dereference
+@cindex no dereference
+Affect symbolic links instead of any referenced file.
+
+@item --reference=@var{rfile}
+@opindex --reference
+@cindex reference file
+Use @var{rfile}'s security context rather than specifying a @var{context} value.
+
+@item -R
+@itemx --recursive
+@opindex -R
+@opindex --recursive
+Operate on files and directories recursively.
+
+@choptH
+@xref{Traversing symlinks}.
+
+@choptL
+@xref{Traversing symlinks}.
+
+@choptP
+@xref{Traversing symlinks}.
+
+@item -v
+@itemx --verbose
+@opindex -v
+@opindex --verbose
+@cindex diagnostic
+Output a diagnostic for every file processed.
+
+@item -u @var{user}
+@itemx --user=@var{user}
+@opindex -u
+@opindex --user
+Set user @var{user} in the target security context.
+
+@item -r @var{role}
+@itemx --role=@var{role}
+@opindex -r
+@opindex --role
+Set role @var{role} in the target security context.
+
+@item -t @var{type}
+@itemx --type=@var{type}
+@opindex -t
+@opindex --type
+Set type @var{type} in the target security context.
+
+@item -l @var{range}
+@itemx --range=@var{range}
+@opindex -l
+@opindex --range
+Set range @var{range} in the target security context.
+
+@end table
+
+@exitstatus
+
+@node runcon invocation
+@section @command{runcon}: Run a command in specified SELinux context
+
+@pindex runcon
+@cindex run with security context
+
+
+@command{runcon} runs file in specified SELinux security context.
+
+Synopses:
+@smallexample
+runcon @var{context} @var{command} [@var{args}]
+runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
+@end smallexample
+
+Run @var{command} with completely-specified @var{context}, or with
+current or transitioned security context modified by one or more of @var{level},
+@var{role}, @var{type} and @var{user}.
+
+If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
+is specified, the first argument is used as the complete context.
+Any additional arguments after @var{command}
+are interpreted as arguments to the command.
+
+With neither @var{context} nor @var{command}, print the current security context.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -c
+@itemx --compute
+@opindex -c
+@opindex --compute
+Compute process transition context before modifying.
+
+@item -u @var{user}
+@itemx --user=@var{user}
+@opindex -u
+@opindex --user
+Set user @var{user} in the target security context.
+
+@item -r @var{role}
+@itemx --role=@var{role}
+@opindex -r
+@opindex --role
+Set role @var{role} in the target security context.
+
+@item -t @var{type}
+@itemx --type=@var{type}
+@opindex -t
+@opindex --type
+Set type @var{type} in the target security context.
+
+@item -l @var{range}
+@itemx --range=@var{range}
+@opindex -l
+@opindex --range
+Set range @var{range} in the target security context.
+
+@end table
+
+@cindex exit status of @command{runcon}
+Exit status:
+
+@display
+126 if @var{command} is found but cannot be invoked
+127 if @command{runcon} itself fails or if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+@node date invocation
+@section @command{date}: Print or set system date and time
+
+@pindex date
+@cindex time, printing or setting
+@cindex printing the current time
+
+Synopses:
+
+@example
+date [@var{option}]@dots{} [+@var{format}]
+date [-u|--utc|--universal] @c this avoids a newline in the output
+[ MMDDhhmm[[CC]YY][.ss] ]
+@end example
+
+@vindex LC_TIME
+Invoking @command{date} with no @var{format} argument is equivalent to invoking
+it with a default format that depends on the @env{LC_TIME} locale category.
+In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
+so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
+
+@vindex TZ
+Normally, @command{date} uses the time zone rules indicated by the
+@env{TZ} environment variable, or the system default rules if @env{TZ}
+is not set. @xref{TZ Variable,, Specifying the Time Zone with
+@env{TZ}, libc, The GNU C Library Reference Manual}.
+
+@findex strftime @r{and @command{date}}
+@cindex time formats
+@cindex formatting times
+If given an argument that starts with a @samp{+}, @command{date} prints the
+current date and time (or the date and time specified by the
+@option{--date} option, see below) in the format defined by that argument,
+which is similar to that of the @code{strftime} function. Except for
+conversion specifiers, which start with @samp{%}, characters in the
+format string are printed unchanged. The conversion specifiers are
+described below.
+
+@exitstatus
+
+@menu
+* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
+* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
+* Literal conversion specifiers:: %[%nt]
+* Padding and other flags:: Pad with zeros, spaces, etc.
+* Setting the time:: Changing the system clock.
+* Options for date:: Instead of the current time.
+@detailmenu
+* Date input formats:: Specifying date strings.
+@end detailmenu
+* Examples of date:: Examples.
+@end menu
+
+@node Time conversion specifiers
+@subsection Time conversion specifiers
+
+@cindex time conversion specifiers
+@cindex conversion specifiers, time
+
+@command{date} conversion specifiers related to times.
+
+@table @samp
+@item %H
+hour (@samp{00}@dots{}@samp{23})
+@item %I
+hour (@samp{01}@dots{}@samp{12})
+@item %k
+hour (@samp{ 0}@dots{}@samp{23}).
+This is a @acronym{GNU} extension.
+@item %l
+hour (@samp{ 1}@dots{}@samp{12}).
+This is a @acronym{GNU} extension.
+@item %M
+minute (@samp{00}@dots{}@samp{59})
+@item %N
+nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
+This is a @acronym{GNU} extension.
+@item %p
+locale's equivalent of either @samp{AM} or @samp{PM};
+blank in many locales.
+Noon is treated as @samp{PM} and midnight as @samp{AM}.
+@item %P
+like @samp{%p}, except lower case.
+This is a @acronym{GNU} extension.
+@item %r
+locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
+@item %R
+24-hour hour and minute. Same as @samp{%H:%M}.
+This is a @acronym{GNU} extension.
+@item %s
+@cindex epoch, seconds since
+@cindex seconds since the epoch
+@cindex beginning of time
+seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
+Leap seconds are not counted unless leap second support is available.
+@xref{%s-examples}, for examples.
+This is a @acronym{GNU} extension.
+@item %S
+second (@samp{00}@dots{}@samp{60}).
+This may be @samp{60} if leap seconds are supported.
+@item %T
+24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
+@item %X
+locale's time representation (e.g., @samp{23:13:48})
+@item %z
+@w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
+(e.g., @samp{-0600} or @samp{+0530}), or nothing if no
+time zone is determinable. This value reflects the numeric time zone
+appropriate for the current time, using the time zone rules specified
+by the @env{TZ} environment variable.
+The time (and optionally, the time zone rules) can be overridden
+by the @option{--date} option.
+This is a @acronym{GNU} extension.
+@item %:z
+@w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
+@samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
+zone is determinable.
+This is a @acronym{GNU} extension.
+@item %::z
+Numeric time zone to the nearest second with @samp{:} (e.g.,
+@samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
+determinable.
+This is a @acronym{GNU} extension.
+@item %:::z
+Numeric time zone with @samp{:} using the minimum necessary precision
+(e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
+no time zone is determinable.
+This is a @acronym{GNU} extension.
+@item %Z
+alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
+time zone is determinable. See @samp{%z} for how it is determined.
+@end table
+
+
+@node Date conversion specifiers
+@subsection Date conversion specifiers
+
+@cindex date conversion specifiers
+@cindex conversion specifiers, date
+
+@command{date} conversion specifiers related to dates.
+
+@table @samp
+@item %a
+locale's abbreviated weekday name (e.g., @samp{Sun})
+@item %A
+locale's full weekday name, variable length (e.g., @samp{Sunday})
+@item %b
+locale's abbreviated month name (e.g., @samp{Jan})
+@item %B
+locale's full month name, variable length (e.g., @samp{January})
+@item %c
+locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
+@item %C
+century. This is like @samp{%Y}, except the last two digits are omitted.
+For example, it is @samp{20} if @samp{%Y} is @samp{2000},
+and is @samp{-0} if @samp{%Y} is @samp{-001}.
+It is normally at least two characters, but it may be more.
+@item %d
+day of month (e.g., @samp{01})
+@item %D
+date; same as @samp{%m/%d/%y}
+@item %e
+day of month, space padded; same as @samp{%_d}
+@item %F
+full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
+This is a good choice for a date format, as it is standard and
+is easy to sort in the usual case where years are in the range
+0000@dots{}9999.
+This is a @acronym{GNU} extension.
+@item %g
+year corresponding to the @acronym{ISO} week number, but without the century
+(range @samp{00} through @samp{99}). This has the same format and value
+as @samp{%y}, except that if the @acronym{ISO} week number (see
+@samp{%V}) belongs
+to the previous or next year, that year is used instead.
+This is a @acronym{GNU} extension.
+@item %G
+year corresponding to the @acronym{ISO} week number. This has the
+same format and value as @samp{%Y}, except that if the @acronym{ISO}
+week number (see
+@samp{%V}) belongs to the previous or next year, that year is used
+instead.
+It is normally useful only if @samp{%V} is also used;
+for example, the format @samp{%G-%m-%d} is probably a mistake,
+since it combines the ISO week number year with the conventional month and day.
+This is a @acronym{GNU} extension.
+@item %h
+same as @samp{%b}
+@item %j
+day of year (@samp{001}@dots{}@samp{366})
+@item %m
+month (@samp{01}@dots{}@samp{12})
+@item %u
+day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
+@item %U
+week number of year, with Sunday as the first day of the week
+(@samp{00}@dots{}@samp{53}).
+Days in a new year preceding the first Sunday are in week zero.
+@item %V
+@acronym{ISO} week number, that is, the
+week number of year, with Monday as the first day of the week
+(@samp{01}@dots{}@samp{53}).
+If the week containing January 1 has four or more days in
+the new year, then it is considered week 1; otherwise, it is week 53 of
+the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
+standard.)
+@item %w
+day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
+@item %W
+week number of year, with Monday as first day of week
+(@samp{00}@dots{}@samp{53}).
+Days in a new year preceding the first Monday are in week zero.
+@item %x
+locale's date representation (e.g., @samp{12/31/99})
+@item %y
+last two digits of year (@samp{00}@dots{}@samp{99})
+@item %Y
+year. This is normally at least four characters, but it may be more.
+Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
+precedes year @samp{0000}.
+@end table
+
+
+@node Literal conversion specifiers
+@subsection Literal conversion specifiers
+
+@cindex literal conversion specifiers
+@cindex conversion specifiers, literal
+
+@command{date} conversion specifiers that produce literal strings.
+
+@table @samp
+@item %%
+a literal %
+@item %n
+a newline
+@item %t
+a horizontal tab
+@end table
+
+
+@node Padding and other flags
+@subsection Padding and other flags
+
+@cindex numeric field padding
+@cindex padding of numeric fields
+@cindex fields, padding numeric
+
+Unless otherwise specified, @command{date} normally pads numeric fields
+with zeros, so that, for
+example, numeric months are always output as two digits.
+Seconds since the epoch are not padded, though,
+since there is no natural width for them.
+
+As a @acronym{GNU} extension, @command{date} recognizes any of the
+following optional flags after the @samp{%}:
+
+@table @samp
+@item -
+(hyphen) Do not pad the field; useful if the output is intended for
+human consumption.
+@item _
+(underscore) Pad with spaces; useful if you need a fixed
+number of characters in the output, but zeros are too distracting.
+@item 0
+(zero) Pad with zeros even if the conversion specifier
+would normally pad with spaces.
+@item ^
+Use upper case characters if possible.
+@item #
+Use opposite case characters if possible.
+A field that is normally upper case becomes lower case, and vice versa.
+@end table
+
+@noindent
+Here are some examples of padding:
+
+@example
+date +%d/%m -d "Feb 1"
+@result{} 01/02
+date +%-d/%-m -d "Feb 1"
+@result{} 1/2
+date +%_d/%_m -d "Feb 1"
+@result{} 1/ 2
+@end example
+
+As a @acronym{GNU} extension, you can specify the field width
+(after any flag, if present) as a decimal number. If the natural size of the
+output of the field has less than the specified number of characters,
+the result is written right adjusted and padded to the given
+size. For example, @samp{%9B} prints the right adjusted month name in
+a field of width 9.
+
+An optional modifier can follow the optional flag and width
+specification. The modifiers are:
+
+@table @samp
+@item E
+Use the locale's alternate representation for date and time. This
+modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
+@samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
+example, @samp{%Ex} might yield a date format based on the Japanese
+Emperors' reigns.
+
+@item O
+Use the locale's alternate numeric symbols for numbers. This modifier
+applies only to numeric conversion specifiers.
+@end table
+
+If the format supports the modifier but no alternate representation
+is available, it is ignored.
+
+
+@node Setting the time
+@subsection Setting the time
+
+@cindex setting the time
+@cindex time setting
+@cindex appropriate privileges
+
+If given an argument that does not start with @samp{+}, @command{date} sets
+the system clock to the date and time specified by that argument (as
+described below). You must have appropriate privileges to set the
+system clock. The @option{--date} and @option{--set} options may not be
+used with such an argument. The @option{--universal} option may be used
+with such an argument to indicate that the specified date and time are
+relative to Coordinated Universal Time rather than to the local time
+zone.
+
+The argument must consist entirely of digits, which have the following
+meaning:
+
+@table @samp
+@item MM
+month
+@item DD
+day within month
+@item hh
+hour
+@item mm
+minute
+@item CC
+first two digits of year (optional)
+@item YY
+last two digits of year (optional)
+@item ss
+second (optional)
+@end table
+
+The @option{--set} option also sets the system clock; see the next section.
+
+
+@node Options for date
+@subsection Options for @command{date}
+
+@cindex @command{date} options
+@cindex options for @command{date}
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -d @var{datestr}
+@itemx --date=@var{datestr}
+@opindex -d
+@opindex --date
+@cindex parsing date strings
+@cindex date strings, parsing
+@cindex arbitrary date strings, parsing
+@opindex yesterday
+@opindex tomorrow
+@opindex next @var{day}
+@opindex last @var{day}
+Display the date and time specified in @var{datestr} instead of the
+current date and time. @var{datestr} can be in almost any common
+format. It can contain month names, time zones, @samp{am} and @samp{pm},
+@samp{yesterday}, etc. For example, @option{--date="2004-02-27
+14:19:13.489392193 +0530"} specifies the instant of time that is
+489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
+time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
+Note: input currently must be in locale independent format. E.g., the
+LC_TIME=C below is needed to print back the correct date in many locales:
+@example
+date -d "$(LC_TIME=C date)"
+@end example
+@xref{Date input formats}.
+
+@item -f @var{datefile}
+@itemx --file=@var{datefile}
+@opindex -f
+@opindex --file
+Parse each line in @var{datefile} as with @option{-d} and display the
+resulting date and time. If @var{datefile} is @samp{-}, use standard
+input. This is useful when you have many dates to process, because the
+system overhead of starting up the @command{date} executable many times can
+be considerable.
+
+@item -r @var{file}
+@itemx --reference=@var{file}
+@opindex -r
+@opindex --reference
+Display the date and time of the last modification of @var{file},
+instead of the current date and time.
+
+@item -R
+@itemx --rfc-822
+@itemx --rfc-2822
+@opindex -R
+@opindex --rfc-822
+@opindex --rfc-2822
+Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
+%z}, evaluated in the C locale so abbreviations are always in English.
+For example:
+
+@example
+Fri, 09 Sep 2005 13:51:39 -0700
+@end example
+
+This format conforms to
+@uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
+@acronym{RFCs} 2822} and
+@uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
+current and previous standards for Internet email.
+
+@item --rfc-3339=@var{timespec}
+@opindex --rfc-3339=@var{timespec}
+Display the date using a format specified by
+@uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
+@acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
+format, except that it also permits applications to use a space rather
+than a @samp{T} to separate dates from times. Unlike the other
+standard formats, @acronym{RFC} 3339 format is always suitable as
+input for the @option{--date} (@option{-d}) and @option{--file}
+(@option{-f}) options, regardless of the current locale.
+
+The argument @var{timespec} specifies how much of the time to include.
+It can be one of the following:
+
+@table @samp
+@item date
+Print just the full-date, e.g., @samp{2005-09-14}.
+This is equivalent to the format @samp{%Y-%m-%d}.
+
+@item seconds
+Print the full-date and full-time separated by a space, e.g.,
+@samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
+time-offset; here the @samp{+05:30} means that local time is five
+hours and thirty minutes east of @acronym{UTC}. This is equivalent to
+the format @samp{%Y-%m-%d %H:%M:%S%:z}.
+
+@item ns
+Like @samp{seconds}, but also print nanoseconds, e.g.,
+@samp{2005-09-14 00:56:06.998458565+05:30}.
+This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
+
+@end table
+
+@item -s @var{datestr}
+@itemx --set=@var{datestr}
+@opindex -s
+@opindex --set
+Set the date and time to @var{datestr}. See @option{-d} above.
+
+@item -u
+@itemx --utc
+@itemx --universal
+@opindex -u
+@opindex --utc
+@opindex --universal
+@cindex Coordinated Universal Time
+@cindex UTC
+@cindex Greenwich Mean Time
+@cindex GMT
+@vindex TZ
+Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
+@env{TZ} environment variable were set to the string @samp{UTC0}.
+Coordinated
+Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
+historical reasons.
+@end table
+
+
+@node Examples of date
+@subsection Examples of @command{date}
+
+@cindex examples of @command{date}
+
+Here are a few examples. Also see the documentation for the @option{-d}
+option in the previous section.
+
+@itemize @bullet
+
+@item
+To print the date of the day before yesterday:
+
+@example
+date --date='2 days ago'
+@end example
+
+@item
+To print the date of the day three months and one day hence:
+
+@example
+date --date='3 months 1 day'
+@end example
+
+@item
+To print the day of year of Christmas in the current year:
+
+@example
+date --date='25 Dec' +%j
+@end example
+
+@item
+To print the current full month name and the day of the month:
+
+@example
+date '+%B %d'
+@end example
+
+But this may not be what you want because for the first nine days of
+the month, the @samp{%d} expands to a zero-padded two-digit field,
+for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
+
+@item
+To print a date without the leading zero for one-digit days
+of the month, you can use the (@acronym{GNU} extension)
+@samp{-} flag to suppress
+the padding altogether:
+
+@example
+date -d 1may '+%B %-d
+@end example
+
+@item
+To print the current date and time in the format required by many
+non-@acronym{GNU} versions of @command{date} when setting the system clock:
+
+@example
+date +%m%d%H%M%Y.%S
+@end example
+
+@item
+To set the system clock forward by two minutes:
+
+@example
+date --set='+2 minutes'
+@end example
+
+@item
+To print the date in @acronym{RFC} 2822 format,
+use @samp{date --rfc-2822}. Here is some example output:
+
+@example
+Fri, 09 Sep 2005 13:51:39 -0700
+@end example
+
+@anchor{%s-examples}
+@item
+To convert a date string to the number of seconds since the epoch
+(which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
+the @samp{%s} format. That can be useful in sorting and/or graphing
+and/or comparing data by date. The following command outputs the
+number of the seconds since the epoch for the time two minutes after the
+epoch:
+
+@example
+date --date='1970-01-01 00:02:00 +0000' +%s
+120
+@end example
+
+If you do not specify time zone information in the date string,
+@command{date} uses your computer's idea of the time zone when
+interpreting the string. For example, if your computer's time zone is
+that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
+seconds) behind UTC:
+
+@example
+# local time zone used
+date --date='1970-01-01 00:02:00' +%s
+18120
+@end example
+
+@item
+If you're sorting or graphing dated data, your raw date values may be
+represented as seconds since the epoch. But few people can look at
+the date @samp{946684800} and casually note ``Oh, that's the first second
+of the year 2000 in Greenwich, England.''
+
+@example
+date --date='2000-01-01 UTC' +%s
+946684800
+@end example
+
+An alternative is to use the @option{--utc} (@option{-u}) option.
+Then you may omit @samp{UTC} from the date string. Although this
+produces the same result for @samp{%s} and many other format sequences,
+with a time zone offset different from zero, it would give a different
+result for zone-dependent formats like @samp{%z}.
+
+@example
+date -u --date=2000-01-01 +%s
+946684800
+@end example
+
+To convert such an unwieldy number of seconds back to
+a more readable form, use a command like this:
+
+@smallexample
+# local time zone used
+date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
+1999-12-31 19:00:00 -0500
+@end smallexample
+
+Or if you do not mind depending on the @samp{@@} feature present since
+coreutils 5.3.0, you could shorten this to:
+
+@smallexample
+date -d @@946684800 +"%F %T %z"
+1999-12-31 19:00:00 -0500
+@end smallexample
+
+Often it is better to output UTC-relative date and time:
+
+@smallexample
+date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
+2000-01-01 00:00:00 +0000
+@end smallexample
+
+@end itemize
+
+
+@node arch invocation
+@section @command{arch}: Print machine hardware name
+
+@pindex arch
+@cindex print machine hardware name
+@cindex system information, printing
+
+@command{arch} prints the machine hardware name,
+and is equivalent to @samp{uname -m}.
+Synopsis:
+
+@example
+arch [@var{option}]
+@end example
+
+The program accepts the @ref{Common options} only.
+
+@exitstatus
+
+
+@node uname invocation
+@section @command{uname}: Print system information
+
+@pindex uname
+@cindex print system information
+@cindex system information, printing
+
+@command{uname} prints information about the machine and operating system
+it is run on. If no options are given, @command{uname} acts as if the
+@option{-s} option were given. Synopsis:
+
+@example
+uname [@var{option}]@dots{}
+@end example
+
+If multiple options or @option{-a} are given, the selected information is
+printed in this order:
+
+@example
+@var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
+@var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
+@end example
+
+The information may contain internal spaces, so such output cannot be
+parsed reliably. In the following example, @var{release} is
+@samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
+
+@smallexample
+uname -a
+@result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
+@end smallexample
+
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+
+@item -a
+@itemx --all
+@opindex -a
+@opindex --all
+Print all of the below information, except omit the processor type
+and the hardware platform name if they are unknown.
+
+@item -i
+@itemx --hardware-platform
+@opindex -i
+@opindex --hardware-platform
+@cindex implementation, hardware
+@cindex hardware platform
+@cindex platform, hardware
+Print the hardware platform name
+(sometimes called the hardware implementation).
+Print @samp{unknown} if the kernel does not make this information
+easily available, as is the case with Linux kernels.
+
+@item -m
+@itemx --machine
+@opindex -m
+@opindex --machine
+@cindex machine type
+@cindex hardware class
+@cindex hardware type
+Print the machine hardware name (sometimes called the hardware class
+or hardware type).
+
+@item -n
+@itemx --nodename
+@opindex -n
+@opindex --nodename
+@cindex hostname
+@cindex node name
+@cindex network node name
+Print the network node hostname.
+
+@item -p
+@itemx --processor
+@opindex -p
+@opindex --processor
+@cindex host processor type
+Print the processor type (sometimes called the instruction set
+architecture or ISA).
+Print @samp{unknown} if the kernel does not make this information
+easily available, as is the case with Linux kernels.
+
+@item -o
+@itemx --operating-system
+@opindex -o
+@opindex --operating-system
+@cindex operating system name
+Print the name of the operating system.
+
+@item -r
+@itemx --kernel-release
+@opindex -r
+@opindex --kernel-release
+@cindex kernel release
+@cindex release of kernel
+Print the kernel release.
+
+@item -s
+@itemx --kernel-name
+@opindex -s
+@opindex --kernel-name
+@cindex kernel name
+@cindex name of kernel
+Print the kernel name.
+@acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
+``the implementation of the operating system'', because the
+@acronym{POSIX} specification itself has no notion of ``kernel''.
+The kernel name might be the same as the operating system name printed
+by the @option{-o} or @option{--operating-system} option, but it might
+differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
+name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
+do not.
+
+@item -v
+@itemx --kernel-version
+@opindex -v
+@opindex --kernel-version
+@cindex kernel version
+@cindex version of kernel
+Print the kernel version.
+
+@end table
+
+@exitstatus
+
+
+@node hostname invocation
+@section @command{hostname}: Print or set system name
+
+@pindex hostname
+@cindex setting the hostname
+@cindex printing the hostname
+@cindex system name, printing
+@cindex appropriate privileges
+
+With no arguments, @command{hostname} prints the name of the current host
+system. With one argument, it sets the current host name to the
+specified string. You must have appropriate privileges to set the host
+name. Synopsis:
+
+@example
+hostname [@var{name}]
+@end example
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@exitstatus
+
+
+@node hostid invocation
+@section @command{hostid}: Print numeric host identifier.
+
+@pindex hostid
+@cindex printing the host identifier
+
+@command{hostid} prints the numeric identifier of the current host
+in hexadecimal. This command accepts no arguments.
+The only options are @option{--help} and @option{--version}.
+@xref{Common options}.
+
+For example, here's what it prints on one system I use:
+
+@example
+$ hostid
+1bac013d
+@end example
+
+On that system, the 32-bit quantity happens to be closely
+related to the system's Internet address, but that isn't always
+the case.
+
+@exitstatus
+
+@node uptime invocation
+@section @command{uptime}: Print system uptime and load
+
+@pindex uptime
+@cindex printing the system uptime and load
+
+@command{uptime} prints the current time, the system's uptime, the
+number of logged-in users and the current load average.
+
+If an argument is specified, it is used as the file to be read
+to discover how many users are logged in. If no argument is
+specified, a system default is used (@command{uptime --help} indicates
+the default setting).
+
+The only options are @option{--help} and @option{--version}.
+@xref{Common options}.
+
+For example, here's what it prints right now on one system I use:
+
+@example
+$ uptime
+ 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
+@end example
+
+The precise method of calculation of load average varies somewhat
+between systems. Some systems calculate it as the average number of
+runnable processes over the last 1, 5 and 15 minutes, but some systems
+also include processes in the uninterruptible sleep state (that is,
+those processes which are waiting for disk I/O). The Linux kernel
+includes uninterruptible processes.
+
+@node Modified command invocation
+@chapter Modified command invocation
+
+@cindex modified command invocation
+@cindex invocation of commands, modified
+@cindex commands for invoking other commands
+
+This section describes commands that run other commands in some context
+different than the current one: a modified environment, as a different
+user, etc.
+
+@menu
+* chroot invocation:: Modify the root directory.
+* env invocation:: Modify environment variables.
+* nice invocation:: Modify niceness.
+* nohup invocation:: Immunize to hangups.
+* su invocation:: Modify user and group ID.
+* timeout invocation:: Run with time limit.
+@end menu
+
+
+@node chroot invocation
+@section @command{chroot}: Run a command with a different root directory
+
+@pindex chroot
+@cindex running a program in a specified root directory
+@cindex root directory, running a program in a specified
+
+@command{chroot} runs a command with a specified root directory.
+On many systems, only the super-user can do this.@footnote{However,
+some systems (e.g., FreeBSD) can be configured to allow certain regular
+users to use the @code{chroot} system call, and hence to run this program.
+Also, on Cygwin, anyone can run the @command{chroot} command, because the
+underlying function is non-privileged due to lack of support in MS-Windows.}
+Synopses:
+
+@example
+chroot @var{newroot} [@var{command} [@var{args}]@dots{}]
+chroot @var{option}
+@end example
+
+Ordinarily, file names are looked up starting at the root of the
+directory structure, i.e., @file{/}. @command{chroot} changes the root to
+the directory @var{newroot} (which must exist) and then runs
+@var{command} with optional @var{args}. If @var{command} is not
+specified, the default is the value of the @env{SHELL} environment
+variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
+@var{command} must not be a special built-in utility
+(@pxref{Special built-in utilities}).
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}. Options must precede operands.
+
+Here are a few tips to help avoid common problems in using chroot.
+To start with a simple example, make @var{command} refer to a statically
+linked binary. If you were to use a dynamically linked executable, then
+you'd have to arrange to have the shared libraries in the right place under
+your new root directory.
+
+For example, if you create a statically linked @command{ls} executable,
+and put it in @file{/tmp/empty}, you can run this command as root:
+
+@example
+$ chroot /tmp/empty /ls -Rl /
+@end example
+
+Then you'll see output like this:
+
+@example
+/:
+total 1023
+-rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
+@end example
+
+If you want to use a dynamically linked executable, say @command{bash},
+then first run @samp{ldd bash} to see what shared objects it needs.
+Then, in addition to copying the actual binary, also copy the listed
+files to the required positions under your intended new root directory.
+Finally, if the executable requires any other files (e.g., data, state,
+device files), copy them into place, too.
+
+@cindex exit status of @command{chroot}
+Exit status:
+
+@display
+1 if @command{chroot} itself fails
+126 if @var{command} is found but cannot be invoked
+127 if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+
+@node env invocation
+@section @command{env}: Run a command in a modified environment
+
+@pindex env
+@cindex environment, running a program in a modified
+@cindex modified environment, running a program in a
+@cindex running a program in a modified environment
+
+@command{env} runs a command with a modified environment. Synopses:
+
+@example
+env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
+[@var{command} [@var{args}]@dots{}]
+env
+@end example
+
+Operands of the form @samp{@var{variable}=@var{value}} set
+the environment variable @var{variable} to value @var{value}.
+@var{value} may be empty (@samp{@var{variable}=}). Setting a variable
+to an empty value is different from unsetting it.
+These operands are evaluated left-to-right, so if two operands
+mention the same variable the earlier is ignored.
+
+Environment variable names can be empty, and can contain any
+characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
+However, it is wise to limit yourself to names that
+consist solely of underscores, digits, and @acronym{ASCII} letters,
+and that begin with a non-digit, as applications like the shell do not
+work well with other names.
+
+@vindex PATH
+The first operand that does not contain the character @samp{=}
+specifies the program to invoke; it is
+searched for according to the @env{PATH} environment variable. Any
+remaining arguments are passed as arguments to that program.
+The program should not be a special built-in utility
+(@pxref{Special built-in utilities}).
+
+@cindex environment, printing
+
+If no command name is specified following the environment
+specifications, the resulting environment is printed. This is like
+specifying the @command{printenv} program.
+
+The program accepts the following options. Also see @ref{Common options}.
+Options must precede operands.
+
+@table @samp
+
+@item -u @var{name}
+@itemx --unset=@var{name}
+@opindex -u
+@opindex --unset
+Remove variable @var{name} from the environment, if it was in the
+environment.
+
+@item -
+@itemx -i
+@itemx --ignore-environment
+@opindex -
+@opindex -i
+@opindex --ignore-environment
+Start with an empty environment, ignoring the inherited environment.
+
+@end table
+
+@cindex exit status of @command{env}
+Exit status:
+
+@display
+0 if no @var{command} is specified and the environment is output
+1 if @command{env} itself fails
+126 if @var{command} is found but cannot be invoked
+127 if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+
+@node nice invocation
+@section @command{nice}: Run a command with modified niceness
+
+@pindex nice
+@cindex niceness
+@cindex scheduling, affecting
+@cindex appropriate privileges
+
+@command{nice} prints or modifies a process's @dfn{niceness},
+a parameter that affects whether the process is scheduled favorably.
+Synopsis:
+
+@example
+nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
+@end example
+
+If no arguments are given, @command{nice} prints the current niceness.
+Otherwise, @command{nice} runs the given @var{command} with its
+niceness adjusted. By default, its niceness is incremented by 10.
+
+Niceness values range at least from @minus{}20 (process has high priority
+and gets more resources, thus slowing down other processes) through 19
+(process has lower priority and runs slowly itself, but has less impact
+on the speed of other running processes). Some systems
+may have a wider range of nicenesses; conversely, other systems may
+enforce more restrictive limits. An attempt to set the niceness
+outside the supported range is treated as an attempt to use the
+minimum or maximum supported value.
+
+A niceness should not be confused with a scheduling priority, which
+lets applications determine the order in which threads are scheduled
+to run. Unlike a priority, a niceness is merely advice to the
+scheduler, which the scheduler is free to ignore. Also, as a point of
+terminology, @acronym{POSIX} defines the behavior of @command{nice} in
+terms of a @dfn{nice value}, which is the nonnegative difference
+between a niceness and the minimum niceness. Though @command{nice}
+conforms to @acronym{POSIX}, its documentation and diagnostics use the
+term ``niceness'' for compatibility with historical practice.
+
+@var{command} must not be a special built-in utility (@pxref{Special
+built-in utilities}).
+
+@mayConflictWithShellBuiltIn{nice}
+
+The program accepts the following option. Also see @ref{Common options}.
+Options must precede operands.
+
+@table @samp
+@item -n @var{adjustment}
+@itemx --adjustment=@var{adjustment}
+@opindex -n
+@opindex --adjustment
+Add @var{adjustment} instead of 10 to the command's niceness. If
+@var{adjustment} is negative and you lack appropriate privileges,
+@command{nice} issues a warning but otherwise acts as if you specified
+a zero adjustment.
+
+For compatibility @command{nice} also supports an obsolete
+option syntax @option{-@var{adjustment}}. New scripts should use
+@option{-n @var{adjustment}} instead.
+
+@end table
+
+@cindex exit status of @command{nice}
+Exit status:
+
+@display
+0 if no @var{command} is specified and the niceness is output
+1 if @command{nice} itself fails
+126 if @var{command} is found but cannot be invoked
+127 if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+It is sometimes useful to run a non-interactive program with reduced niceness.
+
+@example
+$ nice factor 4611686018427387903
+@end example
+
+Since @command{nice} prints the current niceness,
+you can invoke it through itself to demonstrate how it works.
+
+The default behavior is to increase the niceness by @samp{10}:
+
+@example
+$ nice
+0
+$ nice nice
+10
+$ nice -n 10 nice
+10
+@end example
+
+The @var{adjustment} is relative to the current niceness. In the
+next example, the first @command{nice} invocation runs the second one
+with niceness 10, and it in turn runs the final one with a niceness
+that is 3 more:
+
+@example
+$ nice nice -n 3 nice
+13
+@end example
+
+Specifying a niceness larger than the supported range
+is the same as specifying the maximum supported value:
+
+@example
+$ nice -n 10000000000 nice
+19
+@end example
+
+Only a privileged user may run a process with lower niceness:
+
+@example
+$ nice -n -1 nice
+nice: cannot set niceness: Permission denied
+0
+$ sudo nice -n -1 nice
+-1
+@end example
+
+
+@node nohup invocation
+@section @command{nohup}: Run a command immune to hangups
+
+@pindex nohup
+@cindex hangups, immunity to
+@cindex immunity to hangups
+@cindex logging out and continuing to run
+
+@flindex nohup.out
+@command{nohup} runs the given @var{command} with hangup signals ignored,
+so that the command can continue running in the background after you log
+out. Synopsis:
+
+@example
+nohup @var{command} [@var{arg}]@dots{}
+@end example
+
+If standard input is a terminal, it is redirected from
+@file{/dev/null} so that terminal sessions do not mistakenly consider
+the terminal to be used by the command. This is a @acronym{GNU}
+extension; programs intended to be portable to non-@acronym{GNU} hosts
+should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
+instead.
+
+@flindex nohup.out
+If standard output is a terminal, the command's standard output is appended
+to the file @file{nohup.out}; if that cannot be written to, it is appended
+to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
+command is not run.
+Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
+@command{nohup} is made readable and writable only to the user,
+regardless of the current umask settings.
+
+If standard error is a terminal, it is normally redirected to the same file
+descriptor as the (possibly-redirected) standard output.
+However, if standard output is closed, standard error terminal output
+is instead appended to the file @file{nohup.out} or
+@file{$HOME/nohup.out} as above.
+
+To capture the command's output to a file other than @file{nohup.out}
+you can redirect it. For example, to capture the output of
+@command{make}:
+
+@example
+nohup make > make.log
+@end example
+
+@command{nohup} does not automatically put the command it runs in the
+background; you must do that explicitly, by ending the command line
+with an @samp{&}. Also, @command{nohup} does not alter the
+niceness of @var{command}; use @command{nice} for that,
+e.g., @samp{nohup nice @var{command}}.
+
+@var{command} must not be a special built-in utility (@pxref{Special
+built-in utilities}).
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}. Options must precede operands.
+
+@cindex exit status of @command{nohup}
+Exit status:
+
+@display
+126 if @var{command} is found but cannot be invoked
+127 if @command{nohup} itself fails or if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+
+@node su invocation
+@section @command{su}: Run a command with substitute user and group ID
+
+@pindex su
+@cindex substitute user and group IDs
+@cindex user ID, switching
+@cindex super-user, becoming
+@cindex root, becoming
+
+@command{su} allows one user to temporarily become another user. It runs a
+command (often an interactive shell) with the real and effective user
+ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
+
+@example
+su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
+@end example
+
+@cindex passwd entry, and @command{su} shell
+@flindex /bin/sh
+@flindex /etc/passwd
+If no @var{user} is given, the default is @code{root}, the super-user.
+The shell to use is taken from @var{user}'s @code{passwd} entry, or
+@file{/bin/sh} if none is specified there. If @var{user} has a
+password, @command{su} prompts for the password unless run by a user with
+effective user ID of zero (the super-user).
+
+@vindex HOME
+@vindex SHELL
+@vindex USER
+@vindex LOGNAME
+@cindex login shell
+By default, @command{su} does not change the current directory.
+It sets the environment variables @env{HOME} and @env{SHELL}
+from the password entry for @var{user}, and if @var{user} is not
+the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
+By default, the shell is not a login shell.
+
+Any additional @var{arg}s are passed as additional arguments to the
+shell.
+
+@cindex @option{-su}
+GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
+(e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
+to certain shells, etc.).
+
+@findex syslog
+@command{su} can optionally be compiled to use @code{syslog} to report
+failed, and optionally successful, @command{su} attempts. (If the system
+supports @code{syslog}.) However, GNU @command{su} does not check if the
+user is a member of the @code{wheel} group; see below.
+
+The program accepts the following options. Also see @ref{Common options}.
+
+@table @samp
+@item -c @var{command}
+@itemx --command=@var{command}
+@opindex -c
+@opindex --command
+Pass @var{command}, a single command line to run, to the shell with
+a @option{-c} option instead of starting an interactive shell.
+
+@item -f
+@itemx --fast
+@opindex -f
+@opindex --fast
+@flindex .cshrc
+@cindex file name pattern expansion, disabled
+@cindex globbing, disabled
+Pass the @option{-f} option to the shell. This probably only makes sense
+if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
+option prevents reading the startup file (@file{.cshrc}). With
+Bourne-like shells, the @option{-f} option disables file name pattern
+expansion (globbing), which is not likely to be useful.
+
+@item -
+@itemx -l
+@itemx --login
+@opindex -
+@opindex -l
+@opindex --login
+@c other variables already indexed above
+@vindex TERM
+@vindex PATH
+@cindex login shell, creating
+Make the shell a login shell. This means the following. Unset all
+environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
+(which are set as described above), and @env{USER} and @env{LOGNAME}
+(which are set, even for the super-user, as described above), and set
+@env{PATH} to a compiled-in default value. Change to @var{user}'s home
+directory. Prepend @samp{-} to the shell's name, intended to make it
+read its login startup file(s).
+
+@item -m
+@itemx -p
+@itemx --preserve-environment
+@opindex -m
+@opindex -p
+@opindex --preserve-environment
+@cindex environment, preserving
+@flindex /etc/shells
+@cindex restricted shell
+Do not change the environment variables @env{HOME}, @env{USER},
+@env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
+variable @env{SHELL} instead of the shell from @var{user}'s passwd
+entry, unless the user running @command{su} is not the super-user and
+@var{user}'s shell is restricted. A @dfn{restricted shell} is one that
+is not listed in the file @file{/etc/shells}, or in a compiled-in list
+if that file does not exist. Parts of what this option does can be
+overridden by @option{--login} and @option{--shell}.
+
+@item -s @var{shell}
+@itemx --shell=@var{shell}
+@opindex -s
+@opindex --shell
+Run @var{shell} instead of the shell from @var{user}'s passwd entry,
+unless the user running @command{su} is not the super-user and @var{user}'s
+shell is restricted (see @option{-m} just above).
+
+@end table
+
+@cindex exit status of @command{su}
+Exit status:
+
+@display
+1 if @command{su} itself fails
+126 if subshell is found but cannot be invoked
+127 if subshell cannot be found
+the exit status of the subshell otherwise
+@end display
+
+@cindex wheel group, not supported
+@cindex group wheel, not supported
+@cindex fascism
+@subsection Why GNU @command{su} does not support the @samp{wheel} group
+
+(This section is by Richard Stallman.)
+
+@cindex Twenex
+@cindex MIT AI lab
+Sometimes a few of the users try to hold total power over all the
+rest. For example, in 1984, a few users at the MIT AI lab decided to
+seize power by changing the operator password on the Twenex system and
+keeping it secret from everyone else. (I was able to thwart this coup
+and give power back to the users by patching the kernel, but I
+wouldn't know how to do that in Unix.)
+
+However, occasionally the rulers do tell someone. Under the usual
+@command{su} mechanism, once someone learns the root password who
+sympathizes with the ordinary users, he or she can tell the rest. The
+``wheel group'' feature would make this impossible, and thus cement the
+power of the rulers.
+
+I'm on the side of the masses, not that of the rulers. If you are
+used to supporting the bosses and sysadmins in whatever they do, you
+might find this idea strange at first.
+
+
+@node timeout invocation
+@section @command{timeout}: Run a command with a time limit
+
+@pindex timeout
+@cindex time limit
+@cindex run commands with bounded time
+
+@command{timeout} runs the given @var{command} and kills it if it is
+still running after the specified time interval. Synopsis:
+
+@example
+timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
+@end example
+
+@cindex time units
+@var{number} is an integer followed by an optional unit; the default
+is seconds. The units are:
+
+@table @samp
+@item s
+seconds
+@item m
+minutes
+@item h
+hours
+@item d
+days
+@end table
+
+@var{command} must not be a special built-in utility (@pxref{Special
+built-in utilities}).
+
+The program accepts the following option. Also see @ref{Common options}.
+Options must precede operands.
+
+@table @samp
+@item -s @var{signal}
+@itemx --signal=@var{signal}
+@opindex -s
+@opindex --signal
+Send this @var{signal} to @var{command} on timeout, rather than the
+default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
+or a number. Also see @xref{Signal specifications}.
+
+@end table
+
+@cindex exit status of @command{timeout}
+Exit status:
+
+@display
+124 if @var{command} times out
+125 if @command{timeout} itself fails
+126 if @var{command} is found but cannot be invoked
+127 if @var{command} cannot be found
+the exit status of @var{command} otherwise
+@end display
+
+
+@node Process control
+@chapter Process control
+
+@cindex processes, commands for controlling
+@cindex commands for controlling processes
+
+@menu
+* kill invocation:: Sending a signal to processes.
+@end menu
+
+
+@node kill invocation
+@section @command{kill}: Send a signal to processes
+
+@pindex kill
+@cindex send a signal to processes
+
+The @command{kill} command sends a signal to processes, causing them
+to terminate or otherwise act upon receiving the signal in some way.
+Alternatively, it lists information about signals. Synopses:
+
+@example
+kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
+kill [-l | --list | -t | --table] [@var{signal}]@dots{}
+@end example
+
+@mayConflictWithShellBuiltIn{kill}
+
+The first form of the @command{kill} command sends a signal to all
+@var{pid} arguments. The default signal to send if none is specified
+is @samp{TERM}. The special signal number @samp{0} does not denote a
+valid signal, but can be used to test whether the @var{pid} arguments
+specify processes to which a signal could be sent.
+
+If @var{pid} is positive, the signal is sent to the process with the
+process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
+processes in the process group of the current process. If @var{pid}
+is @minus{}1, the signal is sent to all processes for which the user has
+permission to send a signal. If @var{pid} is less than @minus{}1, the signal
+is sent to all processes in the process group that equals the absolute
+value of @var{pid}.
+
+If @var{pid} is not positive, a system-dependent set of system
+processes is excluded from the list of processes to which the signal
+is sent.
+
+If a negative @var{pid} argument is desired as the first one, it
+should be preceded by @option{--}. However, as a common extension to
+@acronym{POSIX}, @option{--} is not required with @samp{kill
+-@var{signal} -@var{pid}}. The following commands are equivalent:
+
+@example
+kill -15 -1
+kill -TERM -1
+kill -s TERM -- -1
+kill -- -1
+@end example
+
+The first form of the @command{kill} command succeeds if every @var{pid}
+argument specifies at least one process that the signal was sent to.
+
+The second form of the @command{kill} command lists signal information.
+Either the @option{-l} or @option{--list} option, or the @option{-t}
+or @option{--table} option must be specified. Without any
+@var{signal} argument, all supported signals are listed. The output
+of @option{-l} or @option{--list} is a list of the signal names, one
+per line; if @var{signal} is already a name, the signal number is
+printed instead. The output of @option{-t} or @option{--table} is a
+table of signal numbers, names, and descriptions. This form of the
+@command{kill} command succeeds if all @var{signal} arguments are valid
+and if there is no output error.
+
+The @command{kill} command also supports the @option{--help} and
+@option{--version} options. @xref{Common options}.
+
+A @var{signal} may be a signal name like @samp{HUP}, or a signal
+number like @samp{1}, or an exit status of a process terminated by the
+signal. A signal name can be given in canonical form or prefixed by
+@samp{SIG}. The case of the letters is ignored, except for the
+@option{-@var{signal}} option which must use upper case to avoid
+ambiguity with lower case option letters. For a list of supported
+signal names and numbers see @xref{Signal specifications}.
+
+@node Delaying
+@chapter Delaying
+
+@cindex delaying commands
+@cindex commands for delaying
+
+@c Perhaps @command{wait} or other commands should be described here also?
+
+@menu
+* sleep invocation:: Delay for a specified time.
+@end menu
+
+
+@node sleep invocation
+@section @command{sleep}: Delay for a specified time
+
+@pindex sleep
+@cindex delay for a specified time
+
+@command{sleep} pauses for an amount of time specified by the sum of
+the values of the command line arguments.
+Synopsis:
+
+@example
+sleep @var{number}[smhd]@dots{}
+@end example
+
+@cindex time units
+Each argument is a number followed by an optional unit; the default
+is seconds. The units are:
+
+@table @samp
+@item s
+seconds
+@item m
+minutes
+@item h
+hours
+@item d
+days
+@end table
+
+Historical implementations of @command{sleep} have required that
+@var{number} be an integer, and only accepted a single argument
+without a suffix. However, GNU @command{sleep} accepts
+arbitrary floating point numbers (using a period before any fractional
+digits).
+
+The only options are @option{--help} and @option{--version}. @xref{Common
+options}.
+
+@c sleep is a shell built-in at least with Solaris 11's /bin/sh
+@mayConflictWithShellBuiltIn{sleep}
+
+@exitstatus
+
+
+@node Numeric operations
+@chapter Numeric operations
+
+@cindex numeric operations
+These programs do numerically-related operations.
+
+@menu
+* factor invocation:: Show factors of numbers.
+* seq invocation:: Print sequences of numbers.
+@end menu
+
+
+@node factor invocation
+@section @command{factor}: Print prime factors
+
+@pindex factor
+@cindex prime factors
+
+@command{factor} prints prime factors. Synopses:
+
+@example
+factor [@var{number}]@dots{}
+factor @var{option}
+@end example
+
+If no @var{number} is specified on the command line, @command{factor} reads
+numbers from standard input, delimited by newlines, tabs, or spaces.
+
+The @command{factor} command supports only a small number of options:
+
+@table @samp
+@item --help
+Print a short help on standard output, then exit without further
+processing.
+
+@item --version
+Print the program version on standard output, then exit without further
+processing.
+@end table
+
+Factoring the product of the eighth and ninth Mersenne primes
+takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
+
+@example
+M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
+/usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
+4951760154835678088235319297: 2147483647 2305843009213693951
+0.03
+@end example
+
+Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
+about 20 seconds on the same machine.
+
+Factoring large prime numbers is, in general, hard. The Pollard Rho
+algorithm used by @command{factor} is particularly effective for
+numbers with relatively small factors. If you wish to factor large
+numbers which do not have small factors (for example, numbers which
+are the product of two large primes), other methods are far better.
+
+If @command{factor} is built without using GNU MP, only
+single-precision arithmetic is available, and so large numbers
+(typically @math{2^{64}} and above) will not be supported. The single-precision
+code uses an algorithm which is designed for factoring smaller
+numbers.
+
+@exitstatus
+
+
+@node seq invocation
+@section @command{seq}: Print numeric sequences
+
+@pindex seq
+@cindex numeric sequences
+@cindex sequence of numbers
+
+@command{seq} prints a sequence of numbers to standard output. Synopses:
+
+@example
+seq [@var{option}]@dots{} @var{last}
+seq [@var{option}]@dots{} @var{first} @var{last}
+seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
+@end example
+
+@command{seq} prints the numbers from @var{first} to @var{last} by
+@var{increment}. By default, each number is printed on a separate line.
+When @var{increment} is not specified, it defaults to @samp{1},
+even when @var{first} is larger than @var{last}.
+@var{first} also defaults to @samp{1}. So @code{seq 1} prints
+@samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
+Floating-point numbers
+may be specified (using a period before any fractional digits).
+
+The program accepts the following options. Also see @ref{Common options}.
+Options must precede operands.
+
+@table @samp
+@item -f @var{format}
+@itemx --format=@var{format}
+@opindex -f @var{format}
+@opindex --format=@var{format}
+@cindex formatting of numbers in @command{seq}
+Print all numbers using @var{format}.
+@var{format} must contain exactly one of the @samp{printf}-style
+floating point conversion specifications @samp{%a}, @samp{%e},
+@samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
+The @samp{%} may be followed by zero or more flags taken from the set
+@samp{-+#0 '}, then an optional width containing one or more digits,
+then an optional precision consisting of a @samp{.} followed by zero
+or more digits. @var{format} may also contain any number of @samp{%%}
+conversion specifications. All conversion specifications have the
+same meaning as with @samp{printf}.
+
+The default format is derived from @var{first}, @var{step}, and
+@var{last}. If these all use a fixed point decimal representation,
+the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
+precision that can represent the output numbers exactly. Otherwise,
+the default format is @samp{%g}.
+
+@item -s @var{string}
+@itemx --separator=@var{string}
+@cindex separator for numbers in @command{seq}
+Separate numbers with @var{string}; default is a newline.
+The output always terminates with a newline.
+
+@item -w
+@itemx --equal-width
+Print all numbers with the same width, by padding with leading zeros.
+@var{first}, @var{step}, and @var{last} should all use a fixed point
+decimal representation.
+(To have other kinds of padding, use @option{--format}).
+
+@end table
+
+You can get finer-grained control over output with @option{-f}:
+
+@example
+$ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
+(-9.00E+05)
+( 2.00E+05)
+( 1.30E+06)
+@end example
+
+If you want hexadecimal integer output, you can use @command{printf}
+to perform the conversion:
+
+@example
+$ printf '%x\n' `seq 1048575 1024 1050623`
+fffff
+1003ff
+1007ff
+@end example
+
+For very long lists of numbers, use xargs to avoid
+system limitations on the length of an argument list:
+
+@example
+$ seq 1000000 | xargs printf '%x\n' | tail -n 3
+f423e
+f423f
+f4240
+@end example
+
+To generate octal output, use the printf @code{%o} format instead
+of @code{%x}.
+
+On most systems, seq can produce whole-number output for values up to
+at least @math{2^{53}}. Larger integers are approximated. The details
+differ depending on your floating-point implementation, but a common
+case is that @command{seq} works with integers through @math{2^{64}},
+and larger integers may not be numerically correct:
+
+@example
+$ seq 18446744073709551616 1 18446744073709551618
+18446744073709551616
+18446744073709551616
+18446744073709551618
+@end example
+
+Be careful when using @command{seq} with outlandish values: otherwise
+you may see surprising results, as @command{seq} uses floating point
+internally. For example, on the x86 platform, where the internal
+representation uses a 64-bit fraction, the command:
+
+@example
+seq 1 0.0000000000000000001 1.0000000000000000009
+@end example
+
+outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
+
+@exitstatus
+
+
+@node File permissions
+@chapter File permissions
+@include perm.texi
+
+@include getdate.texi
+
+@c What's GNU?
+@c Arnold Robbins
+@node Opening the software toolbox
+@chapter Opening the Software Toolbox
+
+An earlier version of this chapter appeared in
+@uref{http://www.linuxjournal.com/article.php?sid=2762, the
+@cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
+It was written by Arnold Robbins.
+
+@menu
+* Toolbox introduction:: Toolbox introduction
+* I/O redirection:: I/O redirection
+* The who command:: The @command{who} command
+* The cut command:: The @command{cut} command
+* The sort command:: The @command{sort} command
+* The uniq command:: The @command{uniq} command
+* Putting the tools together:: Putting the tools together
+@end menu
+
+
+@node Toolbox introduction
+@unnumberedsec Toolbox Introduction
+
+This month's column is only peripherally related to the GNU Project, in
+that it describes a number of the GNU tools on your GNU/Linux system and how they
+might be used. What it's really about is the ``Software Tools'' philosophy
+of program development and usage.
+
+The software tools philosophy was an important and integral concept
+in the initial design and development of Unix (of which Linux and GNU are
+essentially clones). Unfortunately, in the modern day press of
+Internetworking and flashy GUIs, it seems to have fallen by the
+wayside. This is a shame, since it provides a powerful mental model
+for solving many kinds of problems.
+
+Many people carry a Swiss Army knife around in their pants pockets (or
+purse). A Swiss Army knife is a handy tool to have: it has several knife
+blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
+a number of other things on it. For the everyday, small miscellaneous jobs
+where you need a simple, general purpose tool, it's just the thing.
+
+On the other hand, an experienced carpenter doesn't build a house using
+a Swiss Army knife. Instead, he has a toolbox chock full of specialized
+tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
+exactly when and where to use each tool; you won't catch him hammering nails
+with the handle of his screwdriver.
+
+The Unix developers at Bell Labs were all professional programmers and trained
+computer scientists. They had found that while a one-size-fits-all program
+might appeal to a user because there's only one program to use, in practice
+such programs are
+
+@enumerate a
+@item
+difficult to write,
+
+@item
+difficult to maintain and
+debug, and
+
+@item
+difficult to extend to meet new situations.
+@end enumerate
+
+Instead, they felt that programs should be specialized tools. In short, each
+program ``should do one thing well.'' No more and no less. Such programs are
+simpler to design, write, and get right---they only do one thing.
+
+Furthermore, they found that with the right machinery for hooking programs
+together, that the whole was greater than the sum of the parts. By combining
+several special purpose programs, you could accomplish a specific task
+that none of the programs was designed for, and accomplish it much more
+quickly and easily than if you had to write a special purpose program.
+We will see some (classic) examples of this further on in the column.
+(An important additional point was that, if necessary, take a detour
+and build any software tools you may need first, if you don't already
+have something appropriate in the toolbox.)
+
+@node I/O redirection
+@unnumberedsec I/O Redirection
+
+Hopefully, you are familiar with the basics of I/O redirection in the
+shell, in particular the concepts of ``standard input,'' ``standard output,''
+and ``standard error''. Briefly, ``standard input'' is a data source, where
+data comes from. A program should not need to either know or care if the
+data source is a disk file, a keyboard, a magnetic tape, or even a punched
+card reader. Similarly, ``standard output'' is a data sink, where data goes
+to. The program should neither know nor care where this might be.
+Programs that only read their standard input, do something to the data,
+and then send it on, are called @dfn{filters}, by analogy to filters in a
+water pipeline.
+
+With the Unix shell, it's very easy to set up data pipelines:
+
+@smallexample
+program_to_create_data | filter1 | ... | filterN > final.pretty.data
+@end smallexample
+
+We start out by creating the raw data; each filter applies some successive
+transformation to the data, until by the time it comes out of the pipeline,
+it is in the desired form.
+
+This is fine and good for standard input and standard output. Where does the
+standard error come in to play? Well, think about @command{filter1} in
+the pipeline above. What happens if it encounters an error in the data it
+sees? If it writes an error message to standard output, it will just
+disappear down the pipeline into @command{filter2}'s input, and the
+user will probably never see it. So programs need a place where they can send
+error messages so that the user will notice them. This is standard error,
+and it is usually connected to your console or window, even if you have
+redirected standard output of your program away from your screen.
+
+For filter programs to work together, the format of the data has to be
+agreed upon. The most straightforward and easiest format to use is simply
+lines of text. Unix data files are generally just streams of bytes, with
+lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
+conventionally called a ``newline'' in the Unix literature. (This is
+@code{'\n'} if you're a C programmer.) This is the format used by all
+the traditional filtering programs. (Many earlier operating systems
+had elaborate facilities and special purpose programs for managing
+binary data. Unix has always shied away from such things, under the
+philosophy that it's easiest to simply be able to view and edit your
+data with a text editor.)
+
+OK, enough introduction. Let's take a look at some of the tools, and then
+we'll see how to hook them together in interesting ways. In the following
+discussion, we will only present those command line options that interest
+us. As you should always do, double check your system documentation
+for the full story.
+
+@node The who command
+@unnumberedsec The @command{who} Command
+
+The first program is the @command{who} command. By itself, it generates a
+list of the users who are currently logged in. Although I'm writing
+this on a single-user system, we'll pretend that several people are
+logged in:
+
+@example
+$ who
+@print{} arnold console Jan 22 19:57
+@print{} miriam ttyp0 Jan 23 14:19(:0.0)
+@print{} bill ttyp1 Jan 21 09:32(:0.0)
+@print{} arnold ttyp2 Jan 23 20:48(:0.0)
+@end example
+
+Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
+There are three people logged in, and I am logged in twice. On traditional
+Unix systems, user names are never more than eight characters long. This
+little bit of trivia will be useful later. The output of @command{who} is nice,
+but the data is not all that exciting.
+
+@node The cut command
+@unnumberedsec The @command{cut} Command
+
+The next program we'll look at is the @command{cut} command. This program
+cuts out columns or fields of input data. For example, we can tell it
+to print just the login name and full name from the @file{/etc/passwd}
+file. The @file{/etc/passwd} file has seven fields, separated by
+colons:
+
+@example
+arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
+@end example
+
+To get the first and fifth fields, we would use @command{cut} like this:
+
+@example
+$ cut -d: -f1,5 /etc/passwd
+@print{} root:Operator
+@dots{}
+@print{} arnold:Arnold D. Robbins
+@print{} miriam:Miriam A. Robbins
+@dots{}
+@end example
+
+With the @option{-c} option, @command{cut} will cut out specific characters
+(i.e., columns) in the input lines. This is useful for input data
+that has fixed width fields, and does not have a field separator. For
+example, list the Monday dates for the current month:
+
+@c Is using cal ok? Looked at gcal, but I don't like it.
+@example
+$ cal | cut -c 3-5
+@print{}Mo
+@print{}
+@print{} 6
+@print{} 13
+@print{} 20
+@print{} 27
+@end example
+
+@node The sort command
+@unnumberedsec The @command{sort} Command
+
+Next we'll look at the @command{sort} command. This is one of the most
+powerful commands on a Unix-style system; one that you will often find
+yourself using when setting up fancy data plumbing.
+
+The @command{sort}
+command reads and sorts each file named on the command line. It then
+merges the sorted data and writes it to standard output. It will read
+standard input if no files are given on the command line (thus
+making it into a filter). The sort is based on the character collating
+sequence or based on user-supplied ordering criteria.
+
+
+@node The uniq command
+@unnumberedsec The @command{uniq} Command
+
+Finally (at least for now), we'll look at the @command{uniq} program. When
+sorting data, you will often end up with duplicate lines, lines that
+are identical. Usually, all you need is one instance of each line.
+This is where @command{uniq} comes in. The @command{uniq} program reads its
+standard input. It prints only one
+copy of each repeated line. It does have several options. Later on,
+we'll use the @option{-c} option, which prints each unique line, preceded
+by a count of the number of times that line occurred in the input.
+
+
+@node Putting the tools together
+@unnumberedsec Putting the Tools Together
+
+Now, let's suppose this is a large ISP server system with dozens of users
+logged in. The management wants the system administrator to write a program that will
+generate a sorted list of logged in users. Furthermore, even if a user
+is logged in multiple times, his or her name should only show up in the
+output once.
+
+The administrator could sit down with the system documentation and write a C
+program that did this. It would take perhaps a couple of hundred lines
+of code and about two hours to write it, test it, and debug it.
+However, knowing the software toolbox, the administrator can instead start out
+by generating just a list of logged on users:
+
+@example
+$ who | cut -c1-8
+@print{} arnold
+@print{} miriam
+@print{} bill
+@print{} arnold
+@end example
+
+Next, sort the list:
+
+@example
+$ who | cut -c1-8 | sort
+@print{} arnold
+@print{} arnold
+@print{} bill
+@print{} miriam
+@end example
+
+Finally, run the sorted list through @command{uniq}, to weed out duplicates:
+
+@example
+$ who | cut -c1-8 | sort | uniq
+@print{} arnold
+@print{} bill
+@print{} miriam
+@end example
+
+The @command{sort} command actually has a @option{-u} option that does what
+@command{uniq} does. However, @command{uniq} has other uses for which one
+cannot substitute @samp{sort -u}.
+
+The administrator puts this pipeline into a shell script, and makes it available for
+all the users on the system (@samp{#} is the system administrator,
+or @code{root}, prompt):
+
+@example
+# cat > /usr/local/bin/listusers
+who | cut -c1-8 | sort | uniq
+^D
+# chmod +x /usr/local/bin/listusers
+@end example
+
+There are four major points to note here. First, with just four
+programs, on one command line, the administrator was able to save about two
+hours worth of work. Furthermore, the shell pipeline is just about as
+efficient as the C program would be, and it is much more efficient in
+terms of programmer time. People time is much more expensive than
+computer time, and in our modern ``there's never enough time to do
+everything'' society, saving two hours of programmer time is no mean
+feat.
+
+Second, it is also important to emphasize that with the
+@emph{combination} of the tools, it is possible to do a special
+purpose job never imagined by the authors of the individual programs.
+
+Third, it is also valuable to build up your pipeline in stages, as we did here.
+This allows you to view the data at each stage in the pipeline, which helps
+you acquire the confidence that you are indeed using these tools correctly.
+
+Finally, by bundling the pipeline in a shell script, other users can use
+your command, without having to remember the fancy plumbing you set up for
+them. In terms of how you run them, shell scripts and compiled programs are
+indistinguishable.
+
+After the previous warm-up exercise, we'll look at two additional, more
+complicated pipelines. For them, we need to introduce two more tools.
+
+The first is the @command{tr} command, which stands for ``transliterate.''
+The @command{tr} command works on a character-by-character basis, changing
+characters. Normally it is used for things like mapping upper case to
+lower case:
+
+@example
+$ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
+@print{} this example has mixed case!
+@end example
+
+There are several options of interest:
+
+@table @code
+@item -c
+work on the complement of the listed characters, i.e.,
+operations apply to characters not in the given set
+
+@item -d
+delete characters in the first set from the output
+
+@item -s
+squeeze repeated characters in the output into just one character.
+@end table
+
+We will be using all three options in a moment.
+
+The other command we'll look at is @command{comm}. The @command{comm}
+command takes two sorted input files as input data, and prints out the
+files' lines in three columns. The output columns are the data lines
+unique to the first file, the data lines unique to the second file, and
+the data lines that are common to both. The @option{-1}, @option{-2}, and
+@option{-3} command line options @emph{omit} the respective columns. (This is
+non-intuitive and takes a little getting used to.) For example:
+
+@example
+$ cat f1
+@print{} 11111
+@print{} 22222
+@print{} 33333
+@print{} 44444
+$ cat f2
+@print{} 00000
+@print{} 22222
+@print{} 33333
+@print{} 55555
+$ comm f1 f2
+@print{} 00000
+@print{} 11111
+@print{} 22222
+@print{} 33333
+@print{} 44444
+@print{} 55555
+@end example
+
+The file name @file{-} tells @command{comm} to read standard input
+instead of a regular file.
+
+Now we're ready to build a fancy pipeline. The first application is a word
+frequency counter. This helps an author determine if he or she is over-using
+certain words.
+
+The first step is to change the case of all the letters in our input file
+to one case. ``The'' and ``the'' are the same word when doing counting.
+
+@example
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
+@end example
+
+The next step is to get rid of punctuation. Quoted words and unquoted words
+should be treated identically; it's easiest to just get the punctuation out of
+the way.
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
+@end smallexample
+
+The second @command{tr} command operates on the complement of the listed
+characters, which are all the letters, the digits, the underscore, and
+the blank. The @samp{\n} represents the newline character; it has to
+be left alone. (The @acronym{ASCII} tab character should also be included for
+good measure in a production script.)
+
+At this point, we have data consisting of words separated by blank space.
+The words only contain alphanumeric characters (and the underscore). The
+next step is break the data apart so that we have one word per line. This
+makes the counting operation much easier, as we will see shortly.
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
+> tr -s ' ' '\n' | ...
+@end smallexample
+
+This command turns blanks into newlines. The @option{-s} option squeezes
+multiple newline characters in the output into just one. This helps us
+avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
+This is what the shell prints when it notices you haven't finished
+typing in all of a command.)
+
+We now have data consisting of one word per line, no punctuation, all one
+case. We're ready to count each word:
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
+> tr -s ' ' '\n' | sort | uniq -c | ...
+@end smallexample
+
+At this point, the data might look something like this:
+
+@example
+ 60 a
+ 2 able
+ 6 about
+ 1 above
+ 2 accomplish
+ 1 acquire
+ 1 actually
+ 2 additional
+@end example
+
+The output is sorted by word, not by count! What we want is the most
+frequently used words first. Fortunately, this is easy to accomplish,
+with the help of two more @command{sort} options:
+
+@table @code
+@item -n
+do a numeric sort, not a textual one
+
+@item -r
+reverse the order of the sort
+@end table
+
+The final pipeline looks like this:
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
+> tr -s ' ' '\n' | sort | uniq -c | sort -n -r
+@print{} 156 the
+@print{} 60 a
+@print{} 58 to
+@print{} 51 of
+@print{} 51 and
+@dots{}
+@end smallexample
+
+Whew! That's a lot to digest. Yet, the same principles apply. With six
+commands, on two lines (really one long one split for convenience), we've
+created a program that does something interesting and useful, in much
+less time than we could have written a C program to do the same thing.
+
+A minor modification to the above pipeline can give us a simple spelling
+checker! To determine if you've spelled a word correctly, all you have to
+do is look it up in a dictionary. If it is not there, then chances are
+that your spelling is incorrect. So, we need a dictionary.
+The conventional location for a dictionary is @file{/usr/dict/words}.
+On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
+revision of this article.}
+this is a is a sorted, 45,402 word dictionary.
+
+Now, how to compare our file with the dictionary? As before, we generate
+a sorted list of words, one per line:
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
+> tr -s ' ' '\n' | sort -u | ...
+@end smallexample
+
+Now, all we need is a list of words that are @emph{not} in the
+dictionary. Here is where the @command{comm} command comes in.
+
+@smallexample
+$ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
+> tr -s ' ' '\n' | sort -u |
+> comm -23 - /usr/dict/words
+@end smallexample
+
+The @option{-2} and @option{-3} options eliminate lines that are only in the
+dictionary (the second file), and lines that are in both files. Lines
+only in the first file (standard input, our stream of words), are
+words that are not in the dictionary. These are likely candidates for
+spelling errors. This pipeline was the first cut at a production
+spelling checker on Unix.
+
+There are some other tools that deserve brief mention.
+
+@table @command
+@item grep
+search files for text that matches a regular expression
+
+@item wc
+count lines, words, characters
+
+@item tee
+a T-fitting for data pipes, copies data to files and to standard output
+
+@item sed
+the stream editor, an advanced tool
+
+@item awk
+a data manipulation language, another advanced tool
+@end table
+
+The software tools philosophy also espoused the following bit of
+advice: ``Let someone else do the hard part.'' This means, take
+something that gives you most of what you need, and then massage it the
+rest of the way until it's in the form that you want.
+
+To summarize:
+
+@enumerate 1
+@item
+Each program should do one thing well. No more, no less.
+
+@item
+Combining programs with appropriate plumbing leads to results where
+the whole is greater than the sum of the parts. It also leads to novel
+uses of programs that the authors might never have imagined.
+
+@item
+Programs should never print extraneous header or trailer data, since these
+could get sent on down a pipeline. (A point we didn't mention earlier.)
+
+@item
+Let someone else do the hard part.
+
+@item
+Know your toolbox! Use each program appropriately. If you don't have an
+appropriate tool, build one.
+@end enumerate
+
+As of this writing, all the programs we've discussed are available via
+anonymous @command{ftp} from: @*
+@uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
+be more recent versions available now.)
+
+None of what I have presented in this column is new. The Software Tools
+philosophy was first introduced in the book @cite{Software Tools}, by
+Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
+This book showed how to write and use software tools. It was written in
+1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
+FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
+was. The last chapter presented a @command{ratfor} to FORTRAN
+processor, written in @command{ratfor}. @command{ratfor} looks an awful
+lot like C; if you know C, you won't have any problem following the
+code.
+
+In 1981, the book was updated and made available as @cite{Software Tools
+in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
+still in print and are well worth
+reading if you're a programmer. They certainly made a major change in
+how I view programming.
+
+The programs in both books are available from
+@uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
+For a number of years, there was an active
+Software Tools Users Group, whose members had ported the original
+@command{ratfor} programs to essentially every computer system with a
+FORTRAN compiler. The popularity of the group waned in the middle 1980s
+as Unix began to spread beyond universities.
+
+With the current proliferation of GNU code and other clones of Unix programs,
+these programs now receive little attention; modern C versions are
+much more efficient and do more than these programs do. Nevertheless, as
+exposition of good programming style, and evangelism for a still-valuable
+philosophy, these books are unparalleled, and I recommend them highly.
+
+Acknowledgment: I would like to express my gratitude to Brian Kernighan
+of Bell Labs, the original Software Toolsmith, for reviewing this column.
+
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
+
+@include fdl.texi
+
+@node Concept index
+@unnumbered Index
+
+@printindex cp
+
+@bye
+
+@c Local variables:
+@c texinfo-column-for-description: 32
+@c End:
diff -urNp coreutils-7.2-orig/src/ls.c coreutils-7.2/src/ls.c
--- coreutils-7.2-orig/src/ls.c 2010-01-12 15:48:41.000000000 +0100
+++ coreutils-7.2/src/ls.c 2010-01-12 15:49:19.000000000 +0100
@@ -2471,6 +2471,7 @@ print_dir (char const *name, char const
error (0, 0, _("%s: not listing already-listed directory"),
quotearg_colon (name));
closedir (dirp);
+ set_exit_status (true);
return;
}
diff -urNp coreutils-7.2-orig/tests/ls/infloop coreutils-7.2/tests/ls/infloop
--- coreutils-7.2-orig/tests/ls/infloop 2009-02-27 17:36:00.000000000 +0100
+++ coreutils-7.2/tests/ls/infloop 2010-01-12 15:49:19.000000000 +0100
@@ -2,6 +2,7 @@
# show that the following no longer makes ls infloop
# mkdir loop; cd loop; ln -s ../loop sub; ls -RL
+# Also ensure ls exits with status = 2 in that case.
# Copyright (C) 2001-2002, 2004, 2006-2008 Free Software Foundation, Inc.
# This program is free software: you can redistribute it and/or modify
@@ -27,21 +28,22 @@ fi
mkdir loop || framework_failure
ln -s ../loop loop/sub || framework_failure
-fail=0
-
-ls -RL loop 2>err | head -n 7 > out
-# With an inf-looping ls, out will contain these 7 lines:
-cat <<EOF > bad
+cat <<\EOF > exp-out || framework_failure
loop:
sub
+EOF
-loop/sub:
-sub
-
-loop/sub/sub:
+cat <<\EOF > exp-err || framework_failure
+ls: loop/sub: not listing already-listed directory
EOF
-# Make sure we don't get the "bad" output.
-compare out bad > /dev/null 2>&1 && fail=1
+fail=0
+
+timeout 1 ls -RL loop 2>err > out
+# Ensure that ls exits with status 2 upon detecting a cycle
+test $? = 2 || fail=1
+
+compare err exp-err || fail=1
+compare out exp-out || fail=1
Exit $fail