Blob Blame Raw

Archive-Name: editor-faq/sed
Posting-Frequency: irregular
Last-modified: 10 March 2003
Version: 015
URL: http://sed.sourceforge.net/sedfaq.html
Maintainer: Eric Pement (pemente@northpark.edu)

                            THE SED FAQ

                  Frequently Asked Questions about
                       sed, the stream editor

CONTENTS

1. GENERAL INFORMATION
1.1. Introduction - How this FAQ is organized
1.2. Latest version of the sed FAQ
1.3. FAQ revision information
1.4. How do I add a question/answer to the sed FAQ?
1.5. FAQ abbreviations
1.6. Credits and acknowledgements
1.7. Standard disclaimers

2. BASIC SED
2.1. What is sed?
2.2. What versions of sed are there, and where can I get them?

2.2.1. Free versions

2.2.1.1. Unix platforms
2.2.1.2. OS/2
2.2.1.3. Microsoft Windows (Win3x, Win9x, WinNT, Win2K)
2.2.1.4. MS-DOS
2.2.1.5. CP/M
2.2.1.6. Macintosh v8 or v9

2.2.2. Shareware and Commercial versions

2.2.2.1. Unix platforms
2.2.2.2. OS/2
2.2.2.3. Windows 95/98, Windows NT, Windows 2000
2.2.2.4. MS-DOS

2.3. Where can I learn to use sed?

2.3.1. Books
2.3.2. Mailing list
2.3.3. Tutorials, electronic text
2.3.4. General web and ftp sites

3. TECHNICAL
3.1. More detailed explanation of basic sed
3.1.1.  Regular expressions on the left side of "s///"
3.1.2.  Escape characters on the right side of "s///"
3.1.3.  Substitution switches
3.2. Common one-line sed scripts. How do I . . . ?

      - double/triple-space a file?
      - convert DOS/Unix newlines?
      - delete leading/trailing spaces?
      - do substitutions on all/certain lines?
      - delete consecutive blank lines?
      - delete blank lines at the top/end of the file?

3.3. Addressing and address ranges
3.4. Address ranges in GNU sed and HHsed
3.5. Debugging sed scripts
3.6. Notes about s2p, the sed-to-perl translator
3.7. GNU/POSIX extensions to regular expressions

4. EXAMPLES
   ONE-CHARACTER QUESTIONS
4.1.  How do I insert a newline into the RHS of a substitution?
4.2.  How do I represent control-codes or non-printable characters?
4.3.  How do I convert files with toggle characters, like +this+,
      to look like [i]this[/i]?

   CHANGING STRINGS
4.10. How do I perform a case-insensitive search?
4.11. How do I match only the first occurrence of a pattern?
4.12. How do I parse a comma-delimited (CSV) data file?
4.13. How do I handle fixed-length, columnar data?
4.14. How do I commify a string of numbers?
4.15. How do I prevent regex expansion on substitutions?
4.16. How do I convert a string to all lowercase or capital letters?

   CHANGING BLOCKS (consecutive lines)
4.20. How do I change only one section of a file?
4.21. How do I delete or change a block of text if the block contains
      a certain regular expression?
4.22. How do I locate a paragraph of text if the paragraph contains a
      certain regular expression?
4.23. How do I match a block of specific consecutive lines?
4.23.1.  Try to use a "/range/, /expression/"
4.23.2.  Try to use a "multi-line\nexpression"
4.23.3.  Try to use a block of "literal strings"
4.24. How do I address all the lines between RE1 and RE2, excluding the lines themselves?
4.25. How do I join two lines if line #1 ends in a [certain string]?
4.26. How do I join two lines if line #2 begins in a [certain string]?
4.27. How do I change all paragraphs to long lines?

   SHELL AND ENVIRONMENT
4.30.   How do I read environment variables with sed ...
4.31.1.   ... on Unix platforms?
4.31.2.   ... on MS-DOS or 4DOS platforms?
4.32.   How do I export or pass variables back into the environment ...
4.32.1.   ... on Unix platforms?
4.32.2.   ... on MS-DOS or 4DOS platforms?
4.33.   How do I handle shell quoting in sed?

   FILES, DIRECTORIES, AND PATHS
4.40.  How do I read (insert/add) a file at the top of a textfile?
4.41.  How do I make substitutions in every file in a directory, or
        in a complete directory tree?
4.41.1.   ... ssed solution
4.41.2.   ... Unix solution
4.41.3.   ... DOS solution
4.42.  How do I replace "/some/UNIX/path" in a substitution?
4.43.  How do I replace "C:\SOME\DOS\PATH" in a substitution?
4.44.  How do I emulate file-includes, using sed?

5. WHY ISN'T THIS WORKING?
5.1.  Why don't my variables like $var get expanded in my sed script?
5.2.  I'm using 'p' to print, but I have duplicate lines sometimes.
5.3.  Why does my DOS version of sed process a file part-way through
      and then quit?
5.4.  My RE isn't matching/deleting what I want it to. (Or, "Greedy vs.
      stingy pattern matching")
5.5.  What is CSDPMI*B.ZIP and why do I need it?
5.6.  Where are the man pages for GNU sed?
5.7.  How do I tell what version of sed I am using?
5.8.  Does sed issue an exit code?
5.9.  The 'r' command isn't inserting the file into the text.
5.10. Why can't I match or delete a newline using the \n escape
      sequence? Why can't I match 2 or more lines using \n?
5.11. My script aborts with an error message, "event not found".

6. OTHER ISSUES
6.1.  I have a problem that stumps me. Where can I get help?
6.2.  How does sed compare with awk, perl, and other utilities?
6.3.  When should I use sed?
6.4.  When should I NOT use sed?
6.5.  When should I ignore sed and use Awk or Perl instead?
6.6.  Known limitations among sed versions
6.7.  Known incompatibilities between sed versions

6.7.1. Issuing commands from the command line
6.7.2. Using comments (prefixed by the '#' sign)
6.7.3. Special syntax in REs
6.7.4. Word boundaries
6.7.5. Commands which operate differently

7. KNOWN BUGS AMONG SED VERSIONS
7.1. ssed v3.59
7.2. GNU sed v4.0 - v4.0.5
7.3. GNU sed v3.02.80
7.4. GNU sed v3.02
7.5. GNU sed v2.05
7.6. GNU sed v1.18
7.7. GNU sed v1.03
7.8. sed v1.6 (Briscoe)
7.9. sed v1.5 (Helman)
7.10. sedmod v1.0 (Chen)
7.11. HP-UX sed
7.12. SunOS sed v4.1
7.13. SunOS sed v5.6
7.14. Ultrix sed v4.3
7.15. Digital Unix sed


------------------------------

1. GENERAL INFORMATION

1.1. Introduction - How this FAQ is organized

   This FAQ is organized to answer common (and some uncommon)
   questions about sed, quickly. If you see a term or abbreviation in
   the examples that seems unclear, see if the term is defined in
   section 1.5. If not, send your comment to pemente[at]northpark.edu.

1.2. Latest version of the sed FAQ

   The newest version of the sed FAQ is usually here:

       http://sed.sourceforge.net/sedfaq.html (HTML version)
       http://sed.sourceforge.net/sedfaq.txt  (plain text)
       http://www.student.northpark.edu/pemente/sed/sedfaq.html
       http://www.student.northpark.edu/pemente/sed/sedfaq.txt
       http://www.faqs.org/faqs/editor-faq/sed
       ftp://rtfm.mit.edu/pub/faqs/editor-faq/sed

   Another FAQ file on sed by a different author can be found here:

       http://www.dreamwvr.com/sed-info/sed-faq.html

1.3. FAQ revision information

   In the plaintext version, changes are shown by a vertical bar (|)
   placed in column 78 of the affected lines. To remove the vertical
   bars (use double quotes for MS-DOS):

     sed 's/  *|$//' sedfaq.txt > sedfaq2.txt

   In the HTML version, vertical bars do not appear. New or altered
   portions of the FAQ are indicated by printing in dark blue type.

   In the text version, words needing emphasis may be surrounded by
   the underscore '_' or the asterisk '*'. In the HTML version, these
   are changed to italics and boldface, respectively.

1.4. How do I add a question/answer to the sed FAQ?

   Word your question briefly and send it to pemente[at]northpark.edu,
   indicating your proposed change. We'll post it on the sed-users
   mailing list (see section 2.3.2) and discuss it there. If it's
   good, your contribution will be added to the next edition.

1.5. FAQ abbreviations

       files = one or more filenames, separated by whitespace
       gsed  = GNU sed
       ssed  = super-sed
       RE    = Regular Expressions supported by sed
       LHS   = the left-hand side ("find" part) of "s/find/repl/" command
       RHS   = the right-hand side ("replace" part) of "s/find/repl/" cmd
       nn+   = version _nn_ or higher (e.g., "15+" = version 1.5 and above)

   files: "files" stands for one or more filenames entered on the
   command line. The names may include any wildcards your shell
   understands (such as ``zork*'' or ``Aug[4-9].let''). Sed will
   process each filename passed to it by the shell.

   RE: For details on regular expressions, see section 3.1.1., below.

1.6. Credits and acknowledgements

   Many of the ideas for this FAQ were taken from the Awk FAQ:
       http://www.faqs.org/faqs/computer-lang/awk/faq/
       ftp://rtfm.mit.edu/pub/usenet/comp.lang.awk/faq

   and from the old Perl FAQ:
       http://www.perl.com/doc/FAQs/FAQ/oldfaq-html/index.html

   The following individuals have contributed significantly to this
   document, and have provided input and wording suggestions for
   questions, answers, and script examples. Credit goes to these
   contributors (in alphabetical order by last name):

   Al Aab, Yiorgos Adamopoulos, Paolo Bonzini, Walter Briscoe, Jim
   Dennis, Carlos Duarte, Otavio Exel, Sven Guckes, Aurelio Jargas,
   Mark Katz, Toby Kelsey, Eric Pement, Greg Pfeiffer, Ken Pizzini,
   Niall Smart, Simon Taylor, Peter Tillier, Greg Ubben, Laurent
   Vogel.

1.7. Standard disclaimers

   While a serious attempt has been made to ensure the accuracy of the
   information presented herein, the contributors and maintainers of
   this document do not claim the absence of errors and make no
   warranties on the information provided. If you notice any mistakes,
   please let us know so we can fix it.

------------------------------

2. BASIC SED

2.1. What is sed?

   "sed" stands for Stream EDitor. Sed is a non-interactive editor,
   written by the late Lee E. McMahon in 1973 or 1974. A brief history
   of sed's origins may be found in an early history of the Unix
   tools, at <http://www.columbia.edu/~rh120/ch106.x09>.

   Instead of altering a file interactively by moving the cursor on
   the screen (as with a word processor), the user sends a script of
   editing instructions to sed, plus the name of the file to edit (or
   the text to be edited may come as output from a pipe). In this
   sense, sed works like a filter -- deleting, inserting and changing
   characters, words, and lines of text. Its range of activity goes
   from small, simple changes to very complex ones.

   Sed reads its input from stdin (Unix shorthand for "standard
   input," i.e., the console) or from files (or both), and sends the
   results to stdout ("standard output," normally the console or
   screen). Most people use sed first for its substitution features.
   Sed is often used as a find-and-replace tool.

     sed 's/Glenn/Harold/g' oldfile >newfile

   will replace every occurrence of "Glenn" with the word "Harold",
   wherever it occurs in the file. The "find" portion is a regular
   expression ("RE"), which can be a simple word or may contain
   special characters to allow greater flexibility (for example, to
   prevent "Glenn" from also matching "Glennon").

   My very first use of sed was to add 8 spaces to the left side of a
   file, so when I printed it, the printing wouldn't begin at the
   absolute left edge of a piece of paper.

     sed 's/^/        /' myfile >newfile   # my first sed script
     sed 's/^/        /' myfile | lp       # my next sed script

   Then I learned that sed could display only one paragraph of a file,
   beginning at the phrase "and where it came" and ending at the
   phrase "for all people". My script looked like this:

     sed -n '/and where it came/,/for all people/p' myfile

   Sed's normal behavior is to print (i.e., display or show on screen)
   the entire file, including the parts that haven't been altered,
   unless you use the -n switch. The "-n" stands for "no output". This
   switch is almost always used in conjunction with a 'p' command
   somewhere, which says to print only the sections of the file that
   have been specified. The -n switch with the 'p' command allow for
   parts of a file to be printed (i.e., sent to the console).

   Next, I found that sed could show me only (say) lines 12-18 of a
   file and not show me the rest. This was very handy when I needed to
   review only part of a long file and I didn't want to alter it.

     # the 'p' stands for print
     sed -n 12,18p myfile

   Likewise, sed could show me everything else BUT those particular
   lines, without physically changing the file on the disk:

     # the 'd' stands for delete
     sed 12,18d myfile

   Sed could also double-space my single-spaced file when it came time
   to print it:

     sed G myfile >newfile

   If you have many editing commands (for deleting, adding,
   substituting, etc.) which might take up several lines, those
   commands can be put into a separate file and all of the commands in
   the file applied to file being edited:

     #  'script.sed' is the file of commands
     # 'myfile' is the file being changed
     sed -f script.sed myfile  # 'script.sed' is the file of commands

   It is not our intention to convert this FAQ file into a full-blown
   sed tutorial (for good tutorials, see section 2.3). Rather, we hope
   this gives the complete novice a few ideas of how sed can be used.

2.2. What versions of sed are there, and where can I get them?

2.2.1. Free versions

   Note: "Free" does not mean "public domain" nor does it necessarily
   mean you will never be charged for it. All versions of sed in this
   section except the CP/M versions are based on the GNU general
   public license and are "free software" by that standard (for
   details, see http://www.gnu.org/philosophy/free-sw.html). This
   means you can get the source code and develop it further.

   At the URLs listed in this category, sed binaries or source code
   can be downloaded and used without fees or license payments.

2.2.1.1. Unix platforms

   ssed v3.60
   ssed is the version recommended by the FAQ maintainers, since it
   shares the same codebase with GNU sed, has the most options, and is
   free software (you can get the source). Though there were earlier
   version of ssed distributed, sites for these are not being listed.

       http://sed.sourceforge.net/grabbag/ssed
       http://freshmeat.net/project/sed/

   GNU sed v4.0.5
   This is the latest official version of GNU sed. It offers in-place
   text replacement as an option switch.

       ftp://ftp.gnu.org/pub/gnu/sed/sed-4.0.5.tar.gz
       http://freshmeat.net/project/sed

   BSD multi-byte sed (Japanese)
   Based on the latest version of GNU sed, which supports multi-byte
   characters.

       ftp://ftp1.freebsd.org/pub/FreeBSD/FreeBSD-stable/packages/Latest/ja-sed.tgz

   GNU sed v3.02.80
   An alpha test release which was the base for the development of
   ssed and GNU sed v4.0.

       ftp://alpha.gnu.org/pub/gnu/sed/sed-3.02.80.tar.gz

   GNU sed v3.02a
   Interim version with most features of GNU sed v3.02.80.

   GNU sed v3.02
       ftp://ftp.gnu.org/pub/gnu/sed/sed-3.02.tar.gz

   Precompiled versions:

   GNU sed v3.02-8
   source code and binaries for Debian GNU/Linux

       http://www.debian.org/Packages/stable/base/sed.html

   For some time, the GNU project <http://www.gnu.org> used Eric S.
   Raymond's version of sed (ESR sed v1.1), but eventually dropped it
   because it had too many built-in limits. In 1991 Howard Helman
   modified the GNU/ESR sed and produced a flexible version of sed
   v1.5 available at several sites (Helman's version permitted things
   like \<...\> to delimit word boundaries, \xHH to enter hex code and
   \n to indicate newlines in the replace string). This version did
   not catch on with the GNU project and their version of sed has
   moved in a similar but different direction.

   sed v1.3, by Eric Steven Raymond (released 4 June 1998)
       http://catb.org/~esr/sed-1.3.tar.gz

   Eric Raymond <esr@snark.thyrsus.com> wrote one of the earliest
   versions of sed. On his website <http://www.catb.org/~esr/> which
   also distributes many freeware utilities he has written or worked
   on, he describes sed v1.1 this way:

   "This is the fast, small sed originally distributed in the GNU
   toolkit and still distributed with Minix. The GNU people ditched it
   when they built their own sed around an enhanced regex package --
   but it's still better for some uses (in particular, faster and less
   memory-intensive)." (Version 1.3 fixes an unidentified bug and adds
   the L command to hexdump the current pattern space.)

2.2.1.2. OS/2

   GNU sed v3.02.80
       http://www2s.biglobe.ne.jp/~vtgf3mpr/gnu/sed.htm

   GNU sed v3.02
       http://hobbes.nmsu.edu/pub/os2/util/file/sed-3_02-r2-bin.zip # binaries
       http://hobbes.nmsu.edu/pub/os2/util/file/sed-3_02-r2.zip     # source

2.2.1.3. Microsoft Windows (Win3x, Win9x, WinNT, Win2K)

   GNU sed v4.0.5
   32-bit binaries and docs. Precompiled versions not available (yet).

   GNU sed v3.02.80
   32-bit binaries and docs, using DJGPP compiler. For details on new
   features, see Unix section, above.

       http://www.student.northpark.edu/pemente/sed/sed3028a.zip # DOS binaries
       ftp://alpha.gnu.org/pub/gnu/sed/sed-3.02.80.tar.gz        # source
       ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/sed3028b.zip # binaries
       ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/sed3028d.zip # docs
       ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/sed3028s.zip # source

   GNU sed v2.05
   32-bit binaries, no docs. Requires 80386 DX (SX will not run) and
   must be run in a DOS window or in a full screen DOS session under
   Microsoft Windows. Will not run in MS-DOS mode (outside Win/Win95).
   We recommend using the latest version of GNU sed.
       http://www.simtel.net/pub/win95/prog/gsed205b.zip
       ftp://ftp.cdrom.com/pub/simtelnet/win95/prog/gsed205b.zip

   GNU sed v1.03
   modified by Frank Whaley.

   This version was part of the "Virtually UN*X" toolset, hosted by
   itribe.net; that website is now closed. Gsed v1.03 supported Win9x
   long filenames, as well as hex, decimal, binary, and octal
   character representations.

   The Cygwin toolkit:
       http://www.cygwin.com

   Formerly know as "GNU-Win32 tools." According to their home page,
   "The Cygwin tools are Win32 ports of the popular GNU development
   tools for Windows NT, 95 and 98. They function through the use of
   the Cygwin library which provides a UNIX-like API on top of the
   Win32 API." The version of sed used is GNU sed v3.02.

   Minimalist GNU for Windows (MinGW):
       http://www.mingw.org
       http://mingw.sourceforge.net

   According to their home page, "MinGW ('Minimalist GNU for Windows')
   refers to a set of runtime headers, used in building a compiler
   system based on the GNU GCC and binutils projects. It compiles and
   links code to be run on Win32 platforms ... MinGW uses Microsoft
   runtime libraries, distributed with the Windows operating system."
   The version of sed used is GNU sed v3.02.

   sed v1.5 (a/k/a HHsed), by Howard Helman
   Compiled with Mingw32 for 32-bit environments described above. This
   version should support Win95 long filenames.
       http://www.dbnet.ece.ntua.gr/~george/sed/OLD/sed15.exe
       http://www.student.northpark.edu/pemente/sed/sed15exe.zip

2.2.1.4. MS-DOS

   sed v1.6 (from HHsed), by Walter Briscoe

   This is a forthcoming version, now in beta testing, but with many
   new features. It corrects all the bugs in sed v1.5, and adds the
   best features of sedmod v1.0 (below). It is available in 16-bit and
   32-bit compiled versions for MS-DOS. Sorry, no URLs available yet.

   sed v1.5 (a/k/a HHsed), by Howard Helman
   uncompiled source code (Turbo C)
       ftp://ftp.simtel.net/pub/simtelnet/msdos/txtutl/sed15.zip
       ftp://ftp.cdrom.com/pub/simtelnet/msdos/txtutl/sed15.zip

   DOS executable and documentation
       ftp://ftp.simtel.net/pub/simtelnet/msdos/txtutl/sed15x.zip
       ftp://ftp.cdrom.com/pub/simtelnet/msdos/txtutl/sed15x.zip

   sedmod v1.0, by Hern Chen
       http://www.ptug.org/sed/SEDMOD10.ZIP
       http://www.student.northpark.edu/pemente/sed/sedmod10.zip
       ftp://garbo.uwasa.fi/pc/unix/sedmod10.zip

   GNU sed v3.02.80
   See section 2.2.1.3 ("Microsoft Windows"), above.

   GNU sed v2.05
   Does not run under MS-DOS.

   GNU sed v1.18
   32-bit binaries and source, using DJGPP compiler. Requires 80386 SX
   or better. Also requires 3 CWS*.EXE extenders on the path. See
   section 5.5 ("What is CSDPMI*B.ZIP and why do I need it?"), below.
   We recommend using a newer version of GNU sed.
       http://www.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/sed118b.zip
       ftp://ftp.cdrom.com/pub/simtelnet/gnu/djgpp/v2gnu/sed118b.zip
       http://www.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/sed118s.zip
       ftp://ftp.cdrom.com/pub/simtelnet/gnu/djgpp/v2gnu/sed118s.zip

   GNU sed v1.06
   16-bit binaries and source. Should run under any MS-DOS system.
       http://www.simtel.net/pub/gnu/gnuish/sed106.zip
       ftp://ftp.cdrom.com/pub/simtelnet/gnu/gnuish/sed106.zip

2.2.1.5. CP/M

   ssed v2.2, by Chuck A. Forsberg

   Written for CP/M, ssed (for "small/stupid stream editor) supports
   only the a(ppend), c(hange), d(elete) and i(nsert) options, and
   apparently doesn't support regular expressions. A -u switch will
   "unsqueeze" compressed files and was used mainly in conjunction
   with DIF.COM for source code maintenance. (file: ssed22.lbr)

   change, by Michael M. Rubenstein

   Rubenstein released a version of sed called CHANGE.COM (the
   TTOOLS.LBR archive member CHANGE.CZM is a "crunched" file).
   CHANGE.COM supports full RE's except grouping and backreferences,
   and its only function is global substitution. (file: ttools.lbr)

2.2.1.6. Macintosh v8 or v9

   Since sed is a command-line utility, it is not customary to think
   of sed being used on a Mac. Nonetheless, the following instructions
   from Aurelio Jargas describe the process for running sed on MacOS
   version version 8 or 9.

   (1) Download and install the Apple DiskCopy application

       ftp://ftp.apple.com/developer/Development_Kits

   (2) Download and install Apple MPW

       ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/MPW_etc./

   (3) Download and expand Matthias Neeracher's GNU sed for MPW. (They
   seem to have misnumbered the sed filename.)

       ftp://sunsite.cnlab-switch.ch/software/platform/macos/src/mpw_c/sed-2.03.sit.bin

   (4) Enter the sed-3.02 directory and doubleclick the 'sed' file

   (5) MPW Shell will open up. It will be a command window instead of
   a command line, but sed should work as expected. For example:

       echo aa | sed 's/a/Z/g'<ENTER>

   Note that ENTER is different from RETURN on an iMac. Apple *also*
   has its own version of sed on MPW, called "StreamEdit", with a
   syntax fairly similar to that of normal sed.

2.2.2. Shareware and Commercial versions

2.2.2.1. Unix platforms

       [ Additional information needed. ]

2.2.2.2. OS/2

   Hamilton Labs:
       http://www.hamiltonlabs.com/cshell.htm

   A sizable set of Unix/C shell utilities designed for OS/2. Price is
   $350 in the US, $395 elsewhere, with FedEx shipping, unconditional
   guarantee, unlimited support and free updates. A demo version of
   the suite can be downloaded from this site, but a stand-alone copy
   of sed is not available.

2.2.2.3. Windows 95/98, Windows NT, Windows 2000

   Hamilton Labs:
       http://www.hamiltonlabs.com/cshell.htm

   A sizable set of Unix/C shell utilities designed for Win9x, WinNT,
   and Win2K. Price is $350 in the US, $395 elsewhere, with FedEx
   shipping, unconditional guarantee, unlimited support and free
   updates. A demo version of the suite can be downloaded from this
   site, but a stand-alone copy of sed is not available.

   Interix:
       http://www.interix.com

   Interix (formerly known as OpenNT) is advertised as "a complete
   UNIX system environment running natively on Microsoft Windows NT",
   and is licensed and supported by Softway Systems. It offers over
   200 Unix utilities, and supports Unix shells, sockets, networking,
   and more. A single-user edition runs about $200. A free demo or
   evaluation copy will run for 31 days and then quit; to continue
   using it, you must purchase the commercial version.

   MKS NuTCRACKER Professional
       http://www.datafocus.com/products/nutc/

   A different, yet related product line offered by MKS (Mortice Kern
   Systems, below); the awkward spelling "NuTCRACKER" is intentional.
   Various packages offer hundreds of Unix utilities for Win32
   environments. Sed is not available as a separate product.

   UnixDos:
       http://www.unixdos.com

   UnixDos is a suite of 82 Unix utilities ported over to the Windows
   environments. There are 16-bit versions for Win3.x and 32-bit
   versions for WinNT/Win95. It is distributed as uncrippled shareware
   for the first 30 days. After the test period, the utilities will
   not run and you must pay the registration fee of $50.

   Their version of sed supports "\n" in the RHS of expressions, and
   increases the length of input lines to 10,000 characters. By
   special arrangement with the owners, persons who want a licensed
   version of sed *only* (without the other utilities) may pay a
   license fee of $10.

   U/WIN:
       http://www.research.att.com/sw/tools/uwin/

   U/WIN is a suite of Unix utilities created for WinNT and Win95
   systems. It is owned by AT&T, created by David Korn (author of the
   Unix korn shell), and is freely distributed only to educational
   institutions, AT&T employees, or certain researchers; all others
   must pay a fee after a 90-day evaluation period expires. U/WIN
   operates best with the NTFS (WinNT file system) but will run in
   degraded mode with the FAT file system and in further degraded mode
   under Win95. A minimal installation takes about 25 to 30 megs of
   disk space. Sed is not available as a separate file for download,
   but comes with the suite.

2.2.2.4. MS-DOS

   Mix C/Utilities Toolchest
       http://www.mixsoftware.com/product/utility.htm

   According to their web page, "The C/Utilities Toolchest adds over
   40 powerful UNIX utilities to your MS-DOS operating system. The
   result is an environment very similar to UNIX operating systems,
   yet 100% compatible with MS-DOS programs and commands." The
   toolchest costs $19.95, with source code available for an
   additional fee. Mix C's version of sed is not available separately.

   MKS (Mortice Kern Systems) Toolkit
       http://www.mks.com

   Sed comes bundled with the MKS Toolkit, which is distributed only
   as commercial software; it is not available separately.

   Thompson Automation Software
       http://www.tasoft.com

   The Thompson Toolkit contains over 100 familiar Unix utilities,
   including a version of the Unix Korn shell. It runs under MS-DOS,
   OS/2, Win3.x, Win9x, and WinNT. Sed is one of the utilities, though
   Thompson is better known for its version of awk for DOS, TAWK. The
   toolkit runs about $150; sed is not available separately.

2.3. Where can I learn to use sed?

2.3.1. Books

       _Sed & Awk, 2d edition_, by Dale Dougherty & Arnold Robbins
       (Sebastopol, Calif: O'Reilly and Associates, 1997)
       ISBN 1-56592-225-5
       http://www.oreilly.com/catalog/sed2/noframes.html

   About 40 percent of this book is devoted to sed, and maybe 50
   percent is devoted to awk. The other 10 percent covers regexes and
   concepts common to both tools. If you prefer hard copy, this is
   definitely the best single place to learn to use sed, including its
   advanced features.

   The first edition is also very useful. Several typos crept into the
   first printing of the first edition (though if you follow the
   tutorials closely, you'll recognize them right away). A list of
   errors from the first printing of _sed & awk_ is available at
   <http://www.cs.colostate.edu/~dzubera/sedawk.txt>, and errors in
   the 2nd are at <http://www.cs.colostate.edu/~dzubera/sedawk2.txt>,
   though most of these were corrected in later printings. The second
   edition tells how POSIX standards have affected these tools and
   covers the popular GNU versions of sed and awk. Price is about (US)
   $30.00

   -----

       _Mastering Regular Expressions, 2d ed.,_ by Jeffrey E. F. Friedl
       (Sebastopol, Calif: O'Reilly and Associates, 2002)
       ISBN 0-596-00289-0
       http://regex.info
       http://www.oreilly.com/catalog/regex2/
       http://public.yahoo.com/~jfriedl/regex/ (for the first edition)

   Knowing how to use "regular expressions" is essential to effective
   use of most Unix tools. This book focuses on how regular
   expressions can be best implemented in utilities such as perl, vi,
   emacs, and awk, but also touches on sed as well. Friedl's home page
   (above) gives links to other sites which help students learn to
   master regular expressions. His site also gives a Perl script for
   determining a syntactically valid e-mail address, using regexes:

       http://public.yahoo.com/~jfriedl/regex/code.html

   -----

       _Awk und Sed_, by Helmut Herold.
       (Bonn: Addison-Wesley, 1994; 288 pages)
       2nd edition to be released in March 2003
       ISBN 3-8273-2094-1
       http://www.addison-wesley.de/main/main.asp?page=home/bookdetails&ProductID=37214

2.3.2. Mailing list

   If you are interested in learning more about sed (its syntax, using
   regular expressions, etc.) you are welcome to subscribe to a
   sed-oriented mailing list. In fact, there are two mailing lists
   about sed: one in English named "sed-users", moderated by Sven
   Guckes; and one in Portuguese named "sed-BR" (for sed-Brazil),
   moderated by Aurelio Marinho Jargas. The average volume of mail for
   "sed-users" is about 35 messages a week; the average volume of mail
   for "sed-BR" is about 15 messages a week.

       sed-BR mailing list:    http://br.groups.yahoo.com/group/sed-br/
       sed-users mailing list: http://groups.yahoo.com/group/sed-users/

   To subscribe to sed-users, send a blank message to:

       sed-users-subscribe@yahoogroups.com

   To unsubscribe from sed-users, send a blank message to:

       sed-users-unsubscribe@yahoogroups.com

2.3.3. Tutorials, electronic text

   The original users manual for sed, by Lee E. McMahon, from the
   7th edition UNIX Manual (1978), with the classic "Kubla Khan"
   example and tutorial, in formatted text format:
       http://sed.sourceforge.net/grabbag/tutorials/sed_mcmahon.txt

   The source code to the preceding manual. Use "troff -ms sed" to
   print this file properly:
       http://plan9.bell-labs.com/7thEdMan/vol2/sed
       http://cm.bell-labs.com/7thEdMan/vol2/sed

   "Do It With Sed", by Carlos Duarte
       http://www.dbnet.ece.ntua.gr/~george/sed/OLD/sedtut_1.html

   "Sed: How to use sed, a special editor for modifying files
   automatically", by Bruce Barnett and General Electric Company
       http://www.grymoire.com/Unix/Sed.html

   U-SEDIT2.ZIP, by Mike Arst (16 June 1990)
       ftp://ftp.cs.umu.se/pub/pc/u-sedit2.zip
       ftp://ftp.uni-stuttgart.de/pub/systems/msdos/util/unixlike/u-sedit2.zip
       ftp://sunsite.icm.edu.pl/vol/wojsyl/garbo/pc/editor/u-sedit2.zip
       ftp://ftp.sogang.ac.kr/pub/msdos/garbo_pc/editor/u-sedit2.zip

   U-SEDIT3.ZIP, by Mike Arst (24 Jan. 1992)
       http://www.student.northpark.edu/pemente/sed/u-sedit3.zip
       CompuServe DTPFORUM, "PC DTP Utilities" library, file SEDDOC.ZIP

   Another sed FAQ
       http://www.dreamwvr.com/sed-info/sed-faq.html

   sed-tutorial, by Felix von Leitner
       http://www.math.fu-berlin.de/~leitner/sed/tutorial.html

   "Manipulating text with sed," chapter 14 of the SCO OpenServer
   "Operating System Users Guide"
       http://ou800doc.caldera.com/SHL_automate/CTOC-Manipulating_text_with_sed.html

   "Combining the Bourne-shell, sed and awk in the UNIX environment
   for language analysis," by Lothar Schmitt and Kiel Christianson.
   This basic tutorial on the Bourne shell, sed and awk downloads as a
   71-page PostScript file (compressed to 290K with gzip). You may
   need to navigate down from the root to get the file.
       ftp://ftp.u-aizu.ac.jp/u-aizu/doc/Tech-Report/1997/97-2-007.tar.gz
       available upon request from Lothar Schmitt <lothar@u-aizu.ac.jp>

2.3.4. General web and ftp sites

       http://sed.sourceforge.net/grabbag             # Collected scripts
       http://main.rtfiber.com.tw/~changyj/sed/       # Yao-Jen Chang
       http://www.math.fu-berlin.de/~guckes/sed/      # Sven Guckes
       http://www.math.fu-berlin.de/~leitner/sed/     # Felix von Leitner
       http://www.dbnet.ece.ntua.gr/~george/sed/      # Yiorgos Adamopoulos
       http://www.student.northpark.edu/pemente/sed/  # Eric Pement

       http://spacsun.rice.edu/FAQ/sed.html
       ftp://algos.inesc.pt/pub/users/cdua/scripts.tar.gz (sed and shell scripts)

   "Handy One-Liners For Sed", compiled by Eric Pement. A large list
   of 1-line sed commands which can be executed from the command line.
       http://sed.sourceforge.net/sed1line.txt
       http://www.student.northpark.edu/pemente/sed/sed1line.txt

   "Handy One-Liners For Sed", translated to Portuguese
       http://wmaker.lrv.ufsc.br/sed_ptBR.html

   The Single UNIX Specification, Version 3 (technical man page)
       http://www.opengroup.org/onlinepubs/007904975/utilities/sed.html

   Getting started with sed
       http://www.cs.hmc.edu/tech_docs/qref/sed.html

   masm to gas converter
       http://www.delorie.com/djgpp/faq/converting/asm2s-sed.html

   mail2html.zip
       http://www.crispen.org/src/#mail2html

   sample uses of sed in batch files and scripts (Benny Pederson)
       http://users.cybercity.dk/~bse26236/batutil/help/SED.HTM

   dc.sed - the most complex and impressive sed script ever written.
   This sed script by Greg Ubben emulates the Unix dc (desk
   calculator), including base conversion, exponentiation, square
   roots, and much more.
       http://sed.sourceforge.net/grabbag/scripts/dc_overview.htm

   If you should find other tutorials or scripts that should be added
   to this document, please forward the URLs to the FAQ maintainer.

------------------------------

3. TECHNICAL

3.1. More detailed explanation of basic sed

   Sed takes a script of editing commands and applies each command, in
   order, to each line of input. After all the commands have been
   applied to the first line of input, that line is output. A second
   input line is taken for processing, and the cycle repeats. Sed
   scripts can address a single line by line number or by matching a
   /RE pattern/ on the line. An exclamation mark '!' after a regex
   ('/RE/!') or line number will select all lines that do NOT match
   that address. Sed can also address a range of lines in the same
   manner, using a comma to separate the 2 addresses.

     $d               # delete the last line of the file
     /[0-9]\{3\}/p    # print lines with 3 consecutive digits
     5!s/ham/cheese/  # except on line 5, replace 'ham' with 'cheese'
     /awk/!s/aaa/bb/  # unless 'awk' is found, replace 'aaa' with 'bb'
     17,/foo/d        # delete all lines from line 17 up to 'foo'

   Following an address or address range, sed accepts curly braces
   '{...}' so several commands may be applied to that line or to the
   lines matched by the address range. On the command line, semicolons
   ';' separate each instruction and must precede the closing brace.

     sed '/Owner:/{s/yours/mine/g;s/your/my/g;s/you/me/g;}' file

   Range addresses operate differently depending on which version of
   sed is used (see section 3.4, below). For further information on
   using sed, consult the references in section 2.3, above.

3.1.1. Regular expressions on the left side of "s///"

   All versions of sed support Basic Regular Expressions (BREs). For
   the syntax of BREs, enter "man ed" at a Unix shell prompt. A
   technical description of BREs from IEEE POSIX 1003.1-2001 and the
   Single UNIX Specification Version 3 is available online at:
   http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap09.html#tag_09_03

   Sed normally supports BREs plus '\n' to match a newline in the
   pattern space, plus '\xREx' as equivalent to '/RE/', where 'x' is any
   character other than a newline or another backslash.

   Some versions of sed support supersets of BREs, or "extended
   regular expressions", which offer additional metacharacters for
   increased flexibility. For additional information on extended REs
   in GNU sed, see sections 3.7 ("GNU/POSIX extensions to regular
   expressions") and 6.7.3 ("Special syntax in REs"), below.

   Though not required by BREs, some versions of sed support \t to
   represent a TAB, \r for carriage return, \xHH for direct entry of
   hex codes, and so forth. Other versions of sed do not.

   ssed (super-sed) introduced many new features for LHS pattern
   matching, too many to give here. The complete list is found in
   section 6.7.3.H ("ssed"), below.

3.1.2. Escape characters on the right side of "s///"

   The right-hand side (the replacement part) in "s/find/replace/" is
   almost always a string literal, with no interpolation of these
   metacharacters:

       .   ^   $   [   ]   {   }   (   )  ?   +   *   |

   Three things *are* interpolated: ampersand (&), backreferences, and
   options for special seds. An ampersand on the RHS is replaced by
   the entire expression matched on the LHS. There is _never_ any
   reason to use grouping like this:

       s/\(some-complex-regex\)/one two \1 three/

   since you can do this instead:

       s/some-complex-regex/one two & three/

   To enter a literal ampersand on the RHS, type '\&'.

   Grouping and backreferences: All versions of sed support grouping
   and backreferences on the LHS and backreferences only on the RHS.
   Grouping allows a series of characters to be collected in a set,
   indicating the boundaries of the set with \( and \). Then the set
   can be designated to be repeated a certain number of times

       \(like this\)*   or   \(like this\)\{5,7\}.

   Groups can also be nested "\(like \(this\) is here\)" and may
   contain any valid RE. Backreferences repeat the contents of a
   particular group, using a backslash and a digit (1-9) for each
   corresponding group. In other words, "/\(pom\)\1/" is another way
   of writing "/pompom/". If groups are nested, backreference numbers
   are counted by matching \( in strict left to right order.  Thus,
   /..\(the \(word\)\) \("foo"\)../ is matched by the backreference
   \3. Backreferences can be used in the LHS, the RHS, and in normal
   RE addressing (see section 3.3).  Thus,

       /\(.\)\1\(.\)\2\(.\)\3/;      # matches "bookkeeper"
       /^\(.\)\(.\)\(.\)\3\2\1$/;    # finds 6-letter palindromes

   Seds differ in how they treat invalid backreferences where no
   corresponding group occurs. To insert a literal ampersand or
   backslash into the RHS, prefix it with a backslash: \& or \\.

   ssed, sed16, and sedmod permit additional options on the RHS. They
   all support changing part of the replacement string to upper case
   (\u or \U), lower case (\l or \L), or to end case conversion (\E).
   Both sed16 and sedmod support awk-style word references ($1, $2,
   $3, ...) and $0 to insert the entire line before conversion.

     echo ab ghi | sed16 "s/.*/$0 - \U$2/"   # prints "ab ghi - GHI"

   *Note:* This feature of sed16 and sedmod will break sed scripts which
   put a dollar sign and digit into the RHS. Though this is an unlikely
   combination, it's worth remembering if you use other people's scripts.

3.1.3.  Substitution switches

   Standard versions of sed support 4 main flags or switches which may
   be added to the end of an "s///" command. They are:

       N      - Replace the Nth match of the pattern on the LHS, where
                N is an integer between 1 and 512. If N is omitted,
                the default is to replace the first match only.
       g      - Global replace of all matches to the pattern.
       p      - Print the results to stdout, even if -n switch is used.
       w file - Write the pattern space to 'file' if a replacement was
                done. If the file already exists when the script is
                executed, it is overwritten. During script execution,
                w appends to the file for each match.

   GNU sed 3.02 and ssed also offer the /I switch for doing a
   case-insensitive match. For example,

     echo ONE TWO | gsed "s/one/unos/I"      # prints "unos TWO"

   GNU sed 4.x and ssed add the /M switch, to simplify working with
   multi-line patterns: when it is used, ^ or $ will match BOL or EOL.
   \` and \' remain available to match the start and end of pattern
   space, respectively.

   ssed supports two more switches, /S and /X, when its Perl mode is
   used. They are described in detail in section 6.7.3.H, below.

3.1.4. Command-line switches

   All versions of sed support two switches, -e and -n. Though sed
   usually separates multiple commands with semicolons (e.g., "H;d;"),
   certain commands could not accept a semicolon command separator.
   These include :labels, 't', and 'b'. These commands had to occur
   last in a script, separated by -e option switches. For example:

     # The 'ta' means jump to label :a if last s/// returns true
     sed -e :a -e '$!N;s/\n=/ /;ta' -e 'P;D' file

   The -n switch turns off sed's default behavior of printing every
   line. With -n, lines are printed only if explicitly told to. In
   addition, for certain versions of sed, if an external script begins
   with "#n" as its first two characters, the output is suppressed
   (exactly as if -n had been entered on the command line). A list of
   which versions appears in section 6.7.2., below.

   GNU sed 4.x and ssed support additional switches. -l (lowercase L),
   followed by a number, lets you adjust the default length of the 'l'
   and 'L' commands (note that these implementations of sed also
   support an argument to these commands, to tailor the length
   separately of each occurrence of the command).

   -i activates in-place editing (see section 4.41.1, below). -s
   treats each file as a separate stream: sed by default joins all the
   files, so $ represents the last line of the last file; 15 means the
   15th line in the joined stream; and /abc/,/def/ might match across
   files.

   When -s is used, however all addresses refer to single files. For
   example, $ represents the last line of each input file; 15 means
   the 15th line of each input file; and /abc/,/def/ will be "reset"
   (in other words, sed will not execute the commands and start
   looking for /abc/ again) if a file ends before /def/ has been
   matched. Note that -i automatically activates this interpretation
   of addresses.

3.2. Common one-line sed scripts

   A separate document of over 70 handy "one-line" sed commands is
   available at
       http://sed.sourceforge.net/sed1line.txt

   Here are several common sed commands for one-line use. MS-DOS users
   should replace single quotes ('...') with double quotes ("...") in
   these examples. A specific filename usually follows the script,
   though the input may also come via piping or redirection.

   # Double space a file
   sed G file

   # Triple space a file
   sed 'G;G' file

   # Under UNIX: convert DOS newlines (CR/LF) to Unix format
   sed 's/.$//' file    # assumes that all lines end with CR/LF
   sed 's/^M$// file    # in bash/tcsh, press Ctrl-V then Ctrl-M

   # Under DOS: convert Unix newlines (LF) to DOS format
   sed 's/$//' file                     # method 1
   sed -n p file                        # method 2

   # Delete leading whitespace (spaces/tabs) from front of each line
   # (this aligns all text flush left). '^t' represents a true tab
   # character. Under bash or tcsh, press Ctrl-V then Ctrl-I.
   sed 's/^[ ^t]*//' file

   # Delete trailing whitespace (spaces/tabs) from end of each line
   sed 's/[ ^t]*$//' file               # see note on '^t', above

   # Delete BOTH leading and trailing whitespace from each line
   sed 's/^[ ^t]*//;s/[ ^]*$//' file    # see note on '^t', above

   # Substitute "foo" with "bar" on each line
   sed 's/foo/bar/' file        # replaces only 1st instance in a line
   sed 's/foo/bar/4' file       # replaces only 4th instance in a line
   sed 's/foo/bar/g' file       # replaces ALL instances within a line

   # Substitute "foo" with "bar" ONLY for lines which contain "baz"
   sed '/baz/s/foo/bar/g' file

   # Delete all CONSECUTIVE blank lines from file except the first.
   # This method also deletes all blank lines from top and end of file.
   # (emulates "cat -s")
   sed '/./,/^$/!d' file       # this allows 0 blanks at top, 1 at EOF
   sed '/^$/N;/\n$/D' file     # this allows 1 blank at top, 0 at EOF

   # Delete all leading blank lines at top of file (only).
   sed '/./,$!d' file

   # Delete all trailing blank lines at end of file (only).
   sed -e :a -e '/^\n*$/{$d;N;};/\n$/ba' file

   # If a line ends with a backslash, join the next line to it.
   sed -e :a -e '/\\$/N; s/\\\n//; ta' file

   # If a line begins with an equal sign, append it to the previous
   # line (and replace the "=" with a single space).
   sed -e :a -e '$!N;s/\n=/ /;ta' -e 'P;D' file

3.3. Addressing and address ranges

   Sed commands may have an optional "address" or "address range"
   prefix. If there is no address or address range given, then the
   command is applied to all the lines of the input file or text
   stream. Three commands cannot take an address prefix:

      - labels, used to branch or jump within the script
      - the close brace, '}', which ends the '{' "command"
      - the '#' comment character, also technically a "command"

   An address can be a line number (such as 1, 5, 37, etc.), a regular
   expression (written in the form /RE/ or \xREx where 'x' is any
   character other than '\' and RE is the regular expression), or the
   dollar sign ($), representing the last line of the file. An
   exclamation mark (!) after an address or address range will apply
   the command to every line EXCEPT the ones named by the address. A
   null regex ("//") will be replaced by the last regex which was
   used. Also, some seds do not support \xREx as regex delimiters.

     5d               # delete line 5 only
     5!d              # delete every line except line 5
     /RE/s/LHS/RHS/g  # substitute only if RE occurs on the line
     /^$/b label      # if the line is blank, branch to ':label'
     /./!b label      # ... another way to write the same command
     \%.%!b label     # ... yet another way to write this command
     $!N              # on all lines but the last, get the Next line

   Note that an embedded newline can be represented in an address by
   the symbol \n, but this syntax is needed only if the script puts 2
   or more lines into the pattern space via the N, G, or other
   commands. The \n symbol does *not* match the newline at an
   end-of-line because when sed reads each line into the pattern space
   for processing, it strips off the trailing newline, processes the
   line, and adds a newline back when printing the line to standard
   output. To match the end-of-line, use the '$' metacharacter, as
   follows:

     /tape$/       # matches the word 'tape' at the end of a line
     /tape$deck/   # matches the word 'tape$deck' with a literal '$'
     /tape\ndeck/  # matches 'tape' and 'deck' with a newline between

   The following sed commands usually accept *only* a single address.
   All other commands (except labels, '}', and '#') accept both single
   addresses and address ranges.

     =       print to stdout the line number of the current line
     a       after printing the current line, append "text" to stdout
     i       before printing the current line, insert "text" to stdout
     q       quit after the current line is matched
     r file  prints contents of "file" to stdout after line is matched

   Note that we said "usually." If you need to apply the '=', 'a',
   'i', or 'r' commands to each and every line within an address
   range, this behavior can be coerced by the use of braces. Thus,
   "1,9=" is an invalid command, but "1,9{=;}" will print each line
   number followed by its line for the first 9 lines (and then print
   the rest of the rest of the file normally).

   Address ranges occur in the form

       <address1>,<address2>    or    <address1>,<address2>!

   where the address can be a line number or a standard /regex/.
   <address2> can also be a dollar sign, indicating the end of file.
   Under GNU sed 3.02+, ssed, and sed15+, <address2> may also be a
   notation of the form +num, indicating the next _num_ lines after
   <address1> is matched.

   Address ranges are:

   (1) Inclusive. The range "/From here/,/eternity/" matches all the
   lines containing "From here" up to and including the line
   containing "eternity". It will not stop on the line just prior to
   "eternity". (If you don't like this, see section 4.24.)

   (2) Plenary. They always match full lines, not just parts of lines.
   In other words, a command to change or delete an address range will
   change or delete whole lines; it won't stop in the middle of a
   line.

   (3) Multi-linear. Address ranges normally match 2 lines or more.
   The second address will never match the same line the first address
   did; therefore a valid address range always spans at least two
   lines, with these exceptions which match only one line:

      - if the first address matches the last line of the file
      - if using the syntax "/RE/,3" and /RE/ occurs only once in the
        file at line 3 or below
      - if using HHsed v1.5. See section 3.4.

   (4) Minimalist. In address ranges with /regex/ as <address2>, the
   range "/foo/,/bar/" will stop at the first "bar" it finds, provided
   that "bar" occurs on a line below "foo". If the word "bar" occurs
   on several lines below the word "foo", the range will match all the
   lines from the first "foo" up to the first "bar". It will not
   continue hopping ahead to find more "bar"s. In other words, address
   ranges are not "greedy," like regular expressions.

   (5) Repeating. An address range will try to match more than one
   block of lines in a file. However, the blocks cannot nest. In
   addition, a second match will not "take" the last line of the
   previous block.  For example, given the following text,

       start
       stop  start
       stop

   the sed command '/start/,/stop/d' will only delete the first two
   lines. It will not delete all 3 lines.

   (6) Relentless. If the address range finds a "start" match but
   doesn't find a "stop", it will match every line from "start" to the
   end of the file. Thus, beware of the following behaviors:

     /RE1/,/RE2/  # If /RE2/ is not found, matches from /RE1/ to the
                  # end-of-file.

     20,/RE/      # If /RE/ is not found, matches from line 20 to the
                  # end-of-file.

     /RE/,30      # If /RE/ occurs any time after line 30, each
                  # occurrence will be matched in sed15+, sedmod, and
                  # GNU sed v3.02+. GNU sed v2.05 and 1.18 will match
                  # from the 2nd occurrence of /RE/ to the end-of-file.

   If these behaviors seem strange, remember that they occur because
   sed does not look "ahead" in the file. Doing so would stop sed from
   being a stream editor and have adverse effects on its efficiency.
   If these behaviors are undesirable, they can be circumvented or
   corrected by the use of nested testing within braces. The following
   scripts work under GNU sed 3.02:

     # Execute your_commands on range "/RE1/,/RE2/", but if /RE2/ is
     # not found, do nothing.
     /RE1/{:a;N;/RE2/!ba;your_commands;}

     # Execute your_commands on range "20,/RE/", but if /RE/ is not
     # found, do nothing.
     20{:a;N;/RE/!ba;your_commands;}

   As a side note, once we've used N to "slurp" lines together to test
   for the ending expression, the pattern space will have gathered
   many lines (possibly thousands) together and concatenated them as a
   single expression, with the \n sequence marking line breaks. The
   REs *within* the pattern space may have to be modified (e.g., you
   must write '/\nStart/' instead of '/^Start/' and '/[^\n]*/' instead
   of '/.*/') and other standard sed commands will be unavailable or
   difficult to use.

     # Execute your_commands on range "/RE/,30", but if /RE/ occurs
     # on line 31 or later, do not match it.
     1,30{/RE/,$ your_commands;}

   For related suggestions on using address ranges, see sections 4.2,
   4.15, and 4.19 of this FAQ. Also, note the following section.

3.4. Address ranges in GNU sed and HHsed

   (1) GNU sed 3.02+, ssed, and sed15+ all support address ranges like:

       /regex/,+5

   which match /regex/ plus the next 5 lines (or EOF, whichever comes
   first).

   (2) GNU sed v3.02.80 (and above) and ssed support address ranges of:

       0,/regex/

   as a special case to permit matching /regex/ if it occurs on the
   first line. This syntax permits a range expression that matches
   every line from the top of the file to the first instance of
   /regex/, even if /regex/ is on the first line.

   (3) HHsed (sed15) has an exceptional way of implementing

       /regex1/,/regex2/

   If /RE1/ and /RE2/ both occur on the *same* line, HHsed will match
   that single line. In other words, an address range block can
   consist of just one line. HHsed will then look for the next
   occurrence of /regex1/ to begin the block again.

   Every other version of sed (including sed16) requires 2 lines to
   match an address range, and thus /regex1/ and /regex2/ cannot
   successfully match just one line. See also the comments at
   section 7.9.4, below.

   (4) BEGIN~STEP selection: ssed and GNU sed (v2.05 and above) offer
   a form of addressing called "BEGIN~STEP selection". This is *not* a
   range address, which selects an inclusive block of consecutive
   lines from /start/ to /finish/. But I think it seems to belong here.

   Given an expression of the form "M~N", where M and N are integers,
   GNU sed and ssed will select every Nth line, beginning at line M.
   (With gsed v2.05, M had to be less than N, but this restriction is
   no longer necessary). Both M and N may equal 0 ("0~0" selects every
   line). These examples illustrate the syntax:

     sed '1~3d' file      # delete every 3d line, starting with line 1
                          # deletes lines 1, 4, 7, 10, 13, 16, ...

     sed '0~3d' file      # deletes lines 3, 6, 9, 12, 15, 18, ...

     sed -n '2~5p' file   # print every 5th line, starting with line 2
                          # prints lines 2, 7, 12, 17, 22, 27, ...

   (5) Finally, GNU sed v2.05 has a bug in range addressing (see
   section 7.5), which was fixed in the higher versions.


3.5. Debugging sed scripts

   The following two debuggers should make it easier to understand how
   sed scripts operate. They can save hours of grief when trying to
   determine the problems with a sed script.

   (1) sd (sed debugger), by Brian Hiles

   This debugger runs under a Unix shell, is powerful, and is easy to
   use. sd has conditional breakpoints and spypoints of the pattern
   space and hold space, on any scope defined by regex match and/or
   script line number. It can be semi-automated, can save diagnostic
   reports, and shows potential problems with a sed script before it
   tries to execute it. The script is robust and requires the Unix
   shell utilities plus the Bourne shell or Korn shell to execute.

       http://sed.sourceforge.net/grabbag/scripts/sd.ksh.txt (2003)
       http://sed.sourceforge.net/grabbag/scripts/sd.sh.txt  (1998)

   (2) sedsed, by Aurelio Jargas

   This debugger requires Python to run it, and it uses your own
   version of sed, whatever that may be. It displays the current input
   line, the pattern space, and the hold space, before and after each
   sed command is executed.

       http://sedsed.sourceforge.net


3.6. Notes about s2p, the sed-to-perl translator

   s2p (sed to perl) is a Perl program to convert sed scripts into the
   Perl programming language; it is included with many versions of
   Perl. These problems have been found when using s2p:

   (1) Doesn't recognize the semicolon properly after s/// commands.

       s/foo/bar/g;

   (2) Doesn't trim trailing whitespace after s/// commands. Even lone
   trailing spaces, without comments, produce an error.

   (3) Doesn't handle multiple commands within braces. E.g.,

       1,4{=;G;}

   will produce perl code with missing braces, and miss the second "G"
   command as well. In fact, any commands after the first one are
   missed in the perl output script, and the output perl script will
   also contain mismatched braces.

3.7. GNU/POSIX extensions to regular expressions

   GNU sed supports "character classes" in addition to regular
   character sets, such as [0-9A-F]. Like regular character sets,
   character classes represent any single character within a set.

   "Character classes are a new feature introduced in the POSIX
   standard. A character class is a special notation for describing
   lists of characters that have a specific attribute, but where the
   actual characters themselves can vary from country to country
   and/or from character set to character set. For example, the notion
   of what is an alphabetic character differs in the USA and in
   France." [quoted from the docs for GNU awk v3.1.0.]

   Though character classes don't generally conserve space on the
   line, they help make scripts portable for international use. The
   equivalent character sets _for U.S. users_ follows:

     [[:alnum:]]  - [A-Za-z0-9]     Alphanumeric characters
     [[:alpha:]]  - [A-Za-z]        Alphabetic characters
     [[:blank:]]  - [ \x09]         Space or tab characters only
     [[:cntrl:]]  - [\x00-\x19\x7F] Control characters
     [[:digit:]]  - [0-9]           Numeric characters
     [[:graph:]]  - [!-~]           Printable and visible characters
     [[:lower:]]  - [a-z]           Lower-case alphabetic characters
     [[:print:]]  - [ -~]           Printable (non-Control) characters
     [[:punct:]]  - [!-/:-@[-`{-~]  Punctuation characters
     [[:space:]]  - [ \t\v\f]       All whitespace chars
     [[:upper:]]  - [A-Z]           Upper-case alphabetic characters
     [[:xdigit:]] - [0-9a-fA-F]     Hexadecimal digit characters

   Note that [[:graph:]] does not match the space " ", but [[:print:]]
   does. Some character classes may (or may not) match characters in
   the high ASCII range (ASCII 128-255 or 0x80-0xFF), depending on
   which C library was used to compile sed. For non-English languages,
   [[:alpha:]] and other classes may also match high ASCII characters.

------------------------------

4. EXAMPLES

   ONE-CHARACTER QUESTIONS

4.1. How do I insert a newline into the RHS of a substitution?

   Several versions of sed permit '\n' to be typed directly into the
   RHS, which is then converted to a newline on output: ssed,
   gsed302a+, gsed103 (with the -x switch), sed15+, sedmod, and
   UnixDOS sed. The _easiest_ solution is to use one of these
   versions.

   For other versions of sed, try one of the following:

   (a) If typing the sed script from a Bourne shell, use one backslash
   "\" if the script uses 'single quotes' or two backslashes "\\" if
   the script requires "double quotes". In the example below, note
   that the leading '>' on the 2nd line is generated by the shell to
   prompt the user for more input. The user types in slash,
   single-quote, and then ENTER to terminate the command:

     [sh-prompt]$ echo twolines | sed 's/two/& new\
     >/'
     two new
     lines
     [bash-prompt]$

   (b) Use a script file with one backslash '\' in the script,
   immediately followed by a newline. This will embed a newline into
   the "replace" portion. Example:

     sed -f newline.sed files

     # newline.sed
     s/twolines/two new\
     lines/g

   Some versions of sed may not need the trailing backslash. If so,
   remove it.

   (c) Insert an unused character and pipe the output through tr:

     echo twolines | sed 's/two/& new=/' | tr "=" "\n"   # produces
     two new
     lines

   (d) Use the "G" command:

   G appends a newline, plus the contents of the hold space to the end
   of the pattern space. If the hold space is empty, a newline is
   appended anyway. The newline is stored in the pattern space as "\n"
   where it can be addressed by grouping "\(...\)" and moved in the
   RHS. Thus, to change the "twolines" example used earlier, the
   following script will work:

     sed '/twolines/{G;s/\(two\)\(lines\)\(\n\)/\1\3\2/;}'

   (e) Inserting full lines, not breaking lines up:

   If one is not *changing* lines but only inserting complete lines
   before or after a pattern, the procedure is much easier. Use the
   "i" (insert) or "a" (append) command, making the alterations by an
   external script. To insert "This line is new" BEFORE each line
   matching a regex:

     /RE/i This line is new               # HHsed, sedmod, gsed 3.02a
     /RE/{x;s/$/This line is new/;G;}     # other seds

   The two examples above are intended as "one-line" commands entered
   from the console. If using a sed script, "i\" immediately followed
   by a literal newline will work on all versions of sed. Furthermore,
   the command "s/$/This line is new/" will only work if the hold
   space is already empty (which it is by default).

   To append "This line is new" AFTER each line matching a regex:

     /RE/a This line is new               # HHsed, sedmod, gsed 3.02a
     /RE/{G;s/$/This line is new/;}       # other seds

   To append 2 blank lines after each line matching a regex:

     /RE/{G;G;}                    # assumes the hold space is empty

   To replace each line matching a regex with 5 blank lines:

     /RE/{s/.*//;G;G;G;G;}         # assumes the hold space is empty

   (f) Use the "y///" command if possible:

   On some Unix versions of sed (not GNU sed!), though the s///
   command won't accept '\n' in the RHS, the y/// command does. If
   your Unix sed supports it, a newline after "aaa" can be inserted
   this way (which is not portable to GNU sed or other seds):

     s/aaa/&~/; y/~/\n/;    # assuming no other '~' is on the line!

4.2. How do I represent control-codes or nonprintable characters?

   Several versions of sed support the notation \xHH, where "HH" are
   two hex digits, 00-FF: ssed, GNU sed v3.02.80 and above, GNU sed
   v1.03, sed16 and sed15 (HHsed). Try to use one of those versions.

   Sed is not intended to process binary or object code, and files
   which contain nulls (0x00) will usually generate errors in most
   versions of sed. The latest versions of GNU sed and ssed are an
   exception; they permit nulls in the input files and also in
   regexes.

   On Unix platforms, the 'echo' command may allow insertion of octal
   or hex values, e.g., `echo "\0nnn"` or `echo -n "\0nnn"`. The echo
   command may also support syntax like '\\b' or '\\t' for backspace
   or tab characters. Check the man pages to see what syntax your
   version of echo supports. Some versions support the following:

     # replace 0x1A (32 octal) with ASCII letters
     sed 's/'`echo "\032"`'/Ctrl-Z/g'

     # note the 3 backslashes in the command below
     sed "s/.`echo \\\b`//g"

4.3. How do I convert files with toggle characters, like +this+, to
look like [i]this[/i]?

   Input files, especially message-oriented text files, often contain
   toggle characters for emphasis, like ~this~, *this*, or =this=. Sed
   can make the same input pattern produce alternating output each
   time it is encountered. Typical needs might be to generate HMTL
   codes or print codes for boldface, italic, or underscore. This
   script accomodates multiple occurrences of the toggle pattern on
   the same line, as well as cases where the pattern starts on one
   line and finishes several lines later, even at the end of the file:

     # sed script to convert +this+ to [i]this[/i]
     :a
     /+/{ x;        # If "+" is found, switch hold and pattern space
       /^ON/{       # If "ON" is in the (former) hold space, then ..
         s///;      # .. delete it
         x;         # .. switch hold space and pattern space back
         s|+|[/i]|; # .. turn the next "+" into "[/i]"
         ba;        # .. jump back to label :a and start over
       }
     s/^/ON/;       # Else, "ON" was not in the hold space; create it
     x;             # Switch hold space and pattern space
     s|+|[i]|;      # Turn the first "+" into "[i]"
     ba;            # Branch to label :a to find another pattern
     }
     #---end of script---

   This script uses the hold space to create a "flag" to indicate
   whether the toggle is ON or not. We have added remarks to
   illustrate the script logic, but in most versions of sed remarks
   are not permitted after 'b'ranch commands or labels.

   If you are sure that the +toggle+ characters never cross line
   boundaries (i.e., never begin on one line and end on another), this
   script can be reduced to one line:

     s|+\([^+][^+]*\)+|[i]\1[/i]|g

   If your toggle pattern contains regex metacharacters (such as '*'
   or perhaps '+' or '?'), remember to quote them with backslashes.

   CHANGING STRINGS

4.10. How do I perform a case-insensitive search?

   Several versions of sed support case-insensitive matching: ssed and
   GNU sed v3.02+ (with I flag after s/// or /regex/); sedmod with the
   -i switch; and sed16 (which supports both types of switches).

   With other versions of sed, case-insensitive searching is awkward,
   so people may use awk or perl instead, since these programs have
   options for case-insensitive searches. In gawk/mawk, use "BEGIN
   {IGNORECASE=1}" and in perl, "/regex/i". For other seds, here are
   three solutions:

   Solution 1: convert everything to upper case and search normally

     # sed script, solution 1
     h;          # copy the original line to the hold space
                 # convert the pattern space to solid caps
     y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/
                 # now we can search for the word "CARLOS"
     /CARLOS/ {
          # add or insert lines. Note: "s/.../.../" will not work
          # here because we are searching a modified pattern
          # space and are not printing the pattern space.
     }
     x;          # get back the original pattern space
                 # the original pattern space will be printed
     #---end of sed script---

   Solution 2: search for both cases

   Often, proper names will either start with all lower-case ("unix"),
   with an initial capital letter ("Unix") or occur in solid caps
   ("UNIX"). There may be no need to search for every possibility.

     /UNIX/b match
     /[Uu]nix/b match

   Solution 3: search for all possible cases

     # If you must, search for any possible combination
     /[Ca][Aa][Rr][Ll][Oo][Ss]/ { ... }

   Bear in mind that as the pattern length increases, this solution
   becomes an order of magnitude slower than the one of Solution 1, at
   least with some implementations of sed.

4.11. How do I match only the first occurrence of a pattern?

   (1) The general solution is to use GNU sed or ssed, with one of
   these range expressions. The first script ("print only the first
   match") works with any version of sed:

     sed -n '/RE/{p;q;}' file       # print only the first match
     sed '0,/RE/{//d;}' file        # delete only the first match
     sed '0,/RE/s//to_that/' file   # change only the first match

   (2) If you cannot use GNU sed and if you *know* the pattern will
   not occur on the first line, this will work:

     sed '1,/RE/{//d;}' file        # delete only the first match
     sed '1,/RE/s//to_that/' file   # change only the first match

   (3) If you cannot use GNU sed and the pattern *might* occur on the
   first line, use one of the following commands (credit for short GNU
   script goes to Donald Bruce Stewart):

     sed '/RE/{x;/Y/!{s/^/Y/;h;d;};x;}' file       # delete (one way)
     sed -e '/RE/{d;:a' -e '$!N;$ba' -e '}' file   # delete (another way)
     sed '/RE/{d;:a;N;$ba;}' file                  # same script, GNU sed
     sed -e '/RE/{s//to_that/;:a' -e '$!N;$!ba' -e '}' file  # change

   Still another solution, using a flag in the hold space. This is
   portable to all seds and works if the pattern is on the first line:

     # sed script to change "foo" to "bar" only on the first occurrence
     1{x;s/^/first/;x;}
     1,/foo/{x;/first/s///;x;s/foo/bar/;}
     #---end of script---

4.12. How do I parse a comma-delimited (CSV) data file?

   Comma-delimited data files can come in several forms, requiring
   increasing levels of complexity in parsing and handling. They are
   often referred to as CSV files (for "comma separated values") and
   occasionally as SDF files (for "standard data format"). Note that
   some vendors use "SDF" to refer to variable-length records with
   comma-separated fields which are "double-quoted" if they contain
   character values, while other vendors use "SDF" to designate
   fixed-length records with fixed-length, nonquoted fields! (For help
   with fixed-length fields, see question 4.23)

   The term "CSV" became a de-facto standard when Microsoft Excel used
   it as an optional output file format.

   Here are 4 different forms you may encounter in comma-delimited data:

   (a) No quotes, no internal commas

       1001,John Smith,PO Box 123,Chicago,IL,60699
       1002,Mary Jones,320 Main,Denver,CO,84100,

   (b) Like (a), with quotes around each field

       "1003","John Smith","PO Box 123","Chicago","IL","60699"
       "1004","Mary Jones","320 Main","Denver","CO","84100"

   (c) Like (b), with embedded commas

       "1005","Tom Hall, Jr.","61 Ash Ct.","Niles","OH","44446"
       "1006","Bob Davis","429 Pine, Apt. 5","Boston","MA","02128"

   (d) Like (c), with embedded commas and quotes

       "1007","Sue "Red" Smith","19 Main","Troy","MI","48055"
       "1008","Joe "Hey, guy!" Hall","POB 44","Reno","NV","89504"

   In each example above, we have 7 fields and 6 commas which function
   as field separators. Case (c) is a very typical form of these data
   files, with double quotes used to enclose each field and to protect
   internal commas (such as "Tom Hall, Jr.") from interpretation as
   field separators. However, many times the data may include both
   embedded quotation marks as well as embedded commas, as seen by
   case (d), above.

   Case (d) is the closest to Microsoft CSV format. *However*, the
   Microsoft CSV format allows embedded newlines within a
   double-quoted field. If embedded newlines within fields are a
   possibility for your data, you should consider using something
   other than sed to work with the data file.

   Before handling a comma-delimited data file, make sure that you
   fully understand its format and check the integrity of the data.
   Does each line contain the same number of fields? Should certain
   fields be composed only of numbers or of two-letter state
   abbreviations in all caps? Sed (or awk or perl) should be used to
   validate the integrity of the data file before you attempt to alter
   it or extract particular fields from the file.

   After ensuring that each line has a valid number of fields, use sed
   to locate and modify individual fields, using the \(...\) grouping
   command where needed.

   In case (a):

     sed 's/^[^,]*,[^,]*,[^,]*,[^,]*,/.../'
             ^     ^     ^
             |     |     |_ 3rd field
             |     |_______ 2nd field
             |_____________ 1st field

     # Unix script to delete the second field for case (a)
     sed 's/^\([^,]*\),[^,]*,/\1,,/' file

     # Unix script to change field 1 to 9999 for case (a)
     sed 's/^[^,]*,/9999,/' file

   In cases (b) and (c):

     sed 's/^"[^"]*","[^"]*","[^"]*","[^"]*",/.../'
              1st--   2nd--   3rd--   4th--

     # Unix script to delete the second field for case (c)
     sed 's/^\("[^"]*"\),"[^"]*",/\1,"",/' file

     # Unix script to change field 1 to 9999 for case (c)
     sed 's/^"[^"]*",/"9999",/' file


   In case (d):

   One way to parse such files is to replace the 3-character field
   separator "," with an unused character like the tab or vertical
   bar. (Technically, the field separator is only the comma while the
   fields are surrounded by "double quotes", but the net _effect_ is
   that fields are separated by quote-comma-quote, with quote
   characters added to the beginning and end of each record.) Search
   your datafile _first_ to make sure that your character appears
   nowhere in it!

     sed -n '/|/p' file        # search for any instance of '|'
     # if it's not found, we can use the '|' to separate fields

   Then replace the 3-character field separator and parse as before:

     # sed script to delete the second field for case (d)
     s/","/|/g;                  # global change of "," to bar
     s/^\([^|]*\)|[^|]|/\1||/;   # delete 2nd field
     s/|/","/g;                  # global change of bar back to ","
     #---end of script---

     # sed script to change field 1 to 9999 for case (d)
     # Remember to accommodate leading and trailing quote marks
     s/","/|/g;
     s/^[^|]*|/"9999|/;
     s/|/","/g;
     #---end of script---

   Note that this technique works only if _each_ and _every_ field is
   surrounded with double quotes, including empty fields.

   The following solution is for more complex examples of (d), such
   as: not all fields contain "double-quote" marks, or the presence of
   embedded "double-quote" marks within fields, or extraneous
   whitespace around field delimiters. (Thanks to Greg Ubben for this
   script!)

     # sed script to convert case (d) to bar-delimited records
     s/^ *\(.*[^ ]\) *$/|\1|/;
     s/" *, */"|/g;
     : loop
     s/| *\([^",|][^,|]*\) *, */|\1|/g;
     s/| *, */|\1|/g;
     t loop
     s/  *|/|/g;
     s/|  */|/g;
     s/^|\(.*\)|$/\1/;
     #---end of script---

   For example, it turns this (which is badly-formed but legal):

   first,"",unquoted ,""this" is, quoted " ,, sub "quote" inside, f", lone  " empty:

   into this:

   first|""|unquoted|""this" is, quoted "||sub "quote" inside|f"|lone  "   empty:

   Note that the script preserves the "double-quote" marks, but
   changes only the commas where they are used as field separators. I
   have used the vertical bar "|" because it's easier to read, but you
   may change this to another field separator if you wish.

   If your CSV datafile is more complex, it would probably not be
   worth the effort to write it in sed. For such a case, you should
   use Perl with a dedicated CSV module (there are at least two recent
   CSV parsers available from CPAN).

4.13. How do I handle fixed-length, columnar data?

   Sed handles fixed-length fields via \(grouping\) and backreferences
   (\1, \2, \3 ...). If we have 3 fields of 10, 25, and 9 characters
   per field, our sed script might look like so:

     s/^\(.\{10\}\)\(.\{25\}\)\(.\{9\}\)/\3\2\1/;  # Change the fields
        ^^^^^^^^^^^~~~~~~~~~~~==========           #   from 1,2,3 to 3,2,1
         field #1   field #2   field #3

   This is a bit hard to read. By using GNU sed or ssed with the -r
   switch active, it can look like this:

     s/^(.{10})(.{25})(.{9})/\3\2\1/;          # Using the -r switch

   To delete a field in sed, use grouping and omit the backreference
   from the field to be deleted. If the data is long or difficult to
   work with, use ssed with the -R switch and the /x flag after an s///
   command, to insert comments and remarks about the fields.

   For records with many fields, use GNU awk with the FIELDWIDTHS
   variable set in the top of the script. For example:

     awk 'BEGIN{FIELDWIDTHS = "10 25 9"}; {print $3 $2 $1}' file

   This is much easier to read than a similar sed script, especially
   if there are more than 5 or 6 fields to manipulate.

4.14. How do I commify a string of numbers?

   Use the simplest script necessary to accomplish your task. As
   variations of the line increase, the sed script must become more
   complex to handle additional conditions. Whole numbers are
   simplest, followed by decimal formats, followed by embedded words.

   Case 1: simple strings of whole numbers separated by spaces or
   commas, with an optional negative sign. To convert this:

       4381, -1222333, and 70000: - 44555666 1234567890 words
       56890  -234567, and 89222  -999777  345888777666 chars

   to this:

       4,381, -1,222,333, and 70,000: - 44,555,666 1,234,567,890 words
       56,890  -234,567, and 89,222  -999,777  345,888,777,666 chars

   use one of these one-liners:

     sed ':a;s/\B[0-9]\{3\}\>/,&/;ta'                      # GNU sed
     sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'  # other seds

   Case 2: strings of numbers which may have an embedded decimal
   point, separated by spaces or commas, with an optional negative
   sign. To change this:

       4381,  -6555.1212 and 70000,  7.18281828  44906982.071902
       56890   -2345.7778 and 8.0000:  -49000000 -1234567.89012

   to this:

       4,381,  -6,555.1212 and 70,000,  7.18281828  44,906,982.071902
       56,890   -2,345.7778 and 8.0000:  -49,000,000 -1,234,567.89012

   use the following command for GNU sed:

     sed ':a;s/\(^\|[^0-9.]\)\([0-9]\+\)\([0-9]\{3\}\)/\1\2,\3/g;ta'

   and for other versions of sed:

     sed -f case2.sed files

     # case2.sed
     s/^/ /;                 # add space to start of line
     :a
     s/\( [-0-9]\{1,\}\)\([0-9]\{3\}\)/\1,\2/g
     ta
     s/ //;                  # remove space from start of line
     #---end of script---

4.15. How do I prevent regex expansion on substitutions?

   Sometimes you want to *match* regular expression metacharacters as
   literals (e.g., you want to match "[0-9]" or "\n"), to be replaced
   with something else. The ordinary way to prevent expanding
   metacharacters is to prefix them with a backslash. Thus, if "\n"
   matches a newline, "\\n" will match the two-character string of
   'backslash' followed by 'n'.

   But doing this repeatedly can become tedious if there are many
   regexes. The following script will replace alternating strings of
   literals, where no character is interpreted as a regex
   metacharacter:

     # filename: sub_quote.sed
     #   author: Paolo Bonzini
     # sed script to add backslash to find/replace metacharacters
     N;                  # add even numbered line to pattern space
     s,[]/\\$*[],\\&,g;  # quote all of [, ], /, \, $, or *
     s,^,s/,;            # prepend "s/" to front of pattern space
     s,$,/,;             # append "/" to end of pattern space
     s,\n,/,;            # change "\n" to "/", making s/from/to/
     #---end of script---

   Here's a sample of how sub_quote.sed might be used. This example
   converts typical sed regexes to perl-style regexes. The input file
   consists of 10 lines:

       [0-9]
       \d
       [^0-9]
       \D
       \+
       +
       \?
       ?
       \|
       |

   Run the command "sed -f sub_quote.sed input", to transform the
   input file (above) to 5 lines of output:

       s/\[0-9\]/\\d/
       s/\[^0-9\]/\\D/
       s/\\+/+/
       s/\\?/?/
       s/\\|/|/

   The above file is itself a sed script, which can then be used to
   modify other files.

4.16. How do I convert a string to all lowercase or capital letters?

   The easiest method is to use a new version of GNU sed, ssed, sedmod
   or sed16 and employ the \U, \L, or other switches on the right side
   of an s/// command. For example, to convert any word which begins
   with "reg" or "exp" into solid capital letters:

       sed -r "s/\<(reg|exp)[a-z]+/\U&/g"              # gsed4.+ or ssed
       sed "s/\<reg[a-z]+/\U&/g; s/\<exp[a-z]+/\U&/g"  # sed16 and sedmod

   As you can see, sedmod and sed16 do not support alternation (|),
   but they do support case conversion. If none of these versions of
   sed are available to you, some sample scripts for this task are
   available from the Seder's Grab Bag:

       http://sed.sourceforge.net/grabbag/scripts

   Note that some case conversion scripts are listed under "Filename
   manipulation" and others are under "Text formatting."

   CHANGING BLOCKS (consecutive lines)

4.20. How do I change only one section of a file?

   You can match a range of lines by line number, by regexes (say, all
   lines between the words "from" and "until"), or by a combination of
   the two. For multiple substitutions on the same range, put the
   command(s) between braces {...}. For example:

     # replace only between lines 1 and 20
     1,20 s/Johnson/White/g

     # replace everywhere EXCEPT between lines 1 and 20
     1,20 !s/Johnson/White/g

     # replace only between words "from" and "until". Note the
     # use of \<....\> as word boundary markers in GNU sed.
     /from/,/until/ { s/\<red\>/magenta/g; s/\<blue\>/cyan/g; }

     # replace only from the words "ENDNOTES:" to the end of file
     /ENDNOTES:/,$ { s/Schaff/Herzog/g; s/Kraft/Ebbing/g; }

   For technical details on using address ranges, see section 3.3
   ("Addressing and Address ranges").

4.21. How do I delete or change a block of text if the block contains
      a certain regular expression?

   The following deletes the block between 'start' and 'end'
   inclusively, if and only if the block contains the string
   'regex'. Written by Russell Davies, with additional comments:

     # sed script to delete a block if /regex/ matches inside it
     :t
     /start/,/end/ {    # For each line between these block markers..
        /end/!{         #   If we are not at the /end/ marker
           $!{          #     nor the last line of the file,
              N;        #     add the Next line to the pattern space
              bt
           }            #   and branch (loop back) to the :t label.
        }               # This line matches the /end/ marker.
        /regex/d;       # If /regex/ matches, delete the block.
     }                  # Otherwise, the block will be printed.
     #---end of script---

   Note: When the script above reaches /regex/, the entire multi-line
   block is in the pattern space. To replace items inside the block,
   use "s///". To change the entire block, use the 'c' (change)
   command:

     /regex/c\
     1: This will replace the entire block\
     2: with these two lines of text.

4.22. How do I locate a paragraph of text if the paragraph contains a
      certain regular expression?

   Assume that paragraphs are separated by blank lines. For regexes
   that are single terms, use one of the following scripts:

     sed -e '/./{H;$!d;}' -e 'x;/regex/!d'      # most seds
     sed '/./{H;$!d;};x;/regex/!d'              # GNU sed

   To print paragraphs only if they contain 3 specific regular
   expressions (RE1, RE2, and RE3), in any order in the paragraph:

     sed -e '/./{H;$!d;}' -e 'x;/RE1/!d;/RE2/!d;/RE3/!d'

   With this solution and the preceding one, if the paragraphs are
   excessively long (more than 4k in length), you may overflow sed's
   internal buffers. If using HHsed, you must add a "G;" command
   immediately after the "x;" in the scripts above to defeat a bug
   in HHsed (see section 7.9(5), below, for a description).

4.23. How do I match a block of _specific_ consecutive lines?

   There are three ways to approach this problem:

       (1) Try to use a "/range/, /expression/"
       (2) Try to use a "/multi-line\nexpression/"
       (3) Try to use a block of "literal strings"

   We describe each approach in the following sections.

4.23.1.  Try to use a "/range/, /expression/"

   If the block of lines are strings that *never change their order*
   and if the top line never occurs outside the block, like this:

       Abel
       Baker
       Charlie
       Delta

   then these solutions will work for deleting the block:

     sed 's/^Abel$/{N;N;N;d;}' files    # for blocks with few lines
     sed '/^Abel$/, /^Zebra$/d' files   # for blocks with many lines
     sed '/^Abel$/,+25d' files          # HHsed, sedmod, ssed, gsed 3.02.80

   To change the block, use the 'c' (change) command instead of 'd'.
   To print that block only, use the -n switch and 'p' (print) instead
   of 'd'. To change some things inside the block, try this:

     /^Abel$/,/^Delta$/ {
         :ack
         N;
         /\nDelta$/! b ack
         # At this point, all the lines in the block are collected
         s/ubstitute /somethin/g;
     }

4.23.2.  Try to use a "multi-line\nexpression"

   If the top line of the block sometimes appears alone or is
   sometimes followed by other lines, or if a partial block may occur
   somewhere in the file, a multi-line expression may be required.

   In these examples, we give solutions for matching an N-line block.
   The expression "/^RE1\nRE2\nRE3...$/" represents a properly formed
   regular expression where \n indicates a newline between lines. Note
   that the 'N' followed by the 'P;D;' commands forms a "sliding
   window" technique. A window of N lines is formed. If the multi-line
   pattern matches, the block is handled. If not, the top line is
   printed and then deleted from the pattern space, and we try to
   match at the next line.

     # sed script to delete 2 consecutive lines: /^RE1\nRE2$/
     $b
     /^RE1$/ {
       $!N
       /^RE1\nRE2$/d
       P;D
     }
     #---end of script---

     # sed script to delete 3 consecutive lines. (This script
     # fails under GNU sed v2.05 and earlier because of the 't'
     # bug when s///n is used; see section 7.5(1) of the FAQ.)
     : more
     $!N
     s/\n/&/2;
     t enough
     $!b more
     : enough
     /^RE1\nRE2\nRE3$/d
     P;D
     #---end of script---

   For example, to delete a block of 5 consecutive lines, the previous
   script must be altered in only two places:

   (1) Change the 2 in "s/\n/&/2;" to a 4 (the trailing semicolon is
   needed to work around a bug in HHsed v1.5).

   (2) Change the regex line to "/^RE1\nRE2\nRE3\nRE4\nRE5$/d",
   modifying the expression as needed.

   Suppose we want to delete a block of two blank lines followed by
   the word "foo" followed by another blank line (4 lines in all).
   Other blank lines and other instances of "foo" should be left
   alone. After changing the '2' to a '3' (always one number less than
   the total number of lines), the regex line would look like this:
   "/^\n\nfoo\n$/d". (Thanks to Greg Ubben for this script.)

   As an alternative to work around the 't' bug in older versions of
   GNU sed, the following script will delete 4 consecutive lines:

     # sed script to delete 4 consecutive lines. Use this if you
     # require GNU sed 2.05 and below.
     /^RE1$/!b
     $!N
     $!N
     :a
     $b
     N
     /^RE1\nRE2\nRE3\nRE4$/d
     P
     s/^.*\n\(.*\n.*\n.*\)$/\1/
     ba
     #---end of script---

   Its drawback is that it must be modified in 3 places instead of 2
   to adapt it for more lines, and as additional lines are added, the
   's' command is forced to work harder to match the regexes. On the
   other hand, it avoids a bug with gsed-2.05 and illustrates another
   way to solve the problem of deleting consecutive lines.

4.23.3.  Try to use a block of "literal strings"

   If you need to match a static block of text (which may occur any
   number of times throughout a file), where the contents of the block
   are known in advance, then this script is easy to use. It requires
   an intermediate file, which we will call "findrep.txt" (below):

       A block of several consecutive lines to
       be matched literally should be placed on
       top. Regular expressions like .*  or [a-z]
       will lose their special meaning and be
       interpreted literally in this block.
       ----
       Four hyphens separate the two sections. Put
       the replacement text in the lower section.
       As above, sed symbols like &, \n, or \1 will
       lose their special meaning.

   This is a 3-step process. A generic script called "blockrep.sed"
   will read "findrep.txt" (above) and generate a custom script, which
   is then used on the actual input file. In other words,
   "findrep.txt" is a simplified description of the editing that you
   want to do on the block, and "blockrep.sed" turns it into actual
   sed commands.

   Use this process from a Unix shell or from a DOS prompt:

     sed -nf blockrep.sed findrep.txt >custom.sed
     sed -f custom.sed input.file >output.file
     erase custom.sed

   The generic script "blockrep.sed" follows below. It's fairly long.
   Examining its output might help you understanding how to use the
   _sliding window_ technique.

     # filename: blockrep.sed
     #   author: Paolo Bonzini
     # Requires:
     #    (1) blocks to find and replace, e.g., findrep.txt
     #    (2) an input file to be changed, input.file
     #
     # blockrep.sed creates a second sed script, custom.sed,
     # to find the lines above the row of 4 hyphens, globally
     # replacing them with the lower block of text. GNU sed
     # is recommended but not required for this script.
     #
     # Loop on the first part, accumulating the `from' text
     # into the hold space.
     :a
     /^----$/! {
        # Escape slashes, backslashes, the final newline and
        # regular expression metacharacters.
        s,[/\[.*],\\&,g
        s/$/\\/
        H
        #
        # Append N cmds needed to maintain the sliding window.
        x
        1 s,^.,s/,
        1! s/^/N\
     /
        x
        n
        ba
     }
     #
     # Change the final backslash to a slash to separate the
     # two sides of the s command.
     x
     s,\\$,/,
     x
     #
     # Until EOF, gather the substitution into hold space.
     :b
     n
     s,[/\],\\&,g
     $! s/$/\\/
     H
     $! bb
     #
     # Start the RHS of the s command without a leading
     # newline, add the P/D pair for the sliding window, and
     # print the script.
     g
     s,/\n,/,
     s,$,/\
     P\
     D,p
     #---end of script---

4.24. How do I address all the lines between RE1 and RE2, excluding the
      lines themselves?

   Normally, to address the lines between two regular expressions, RE1
   and RE2, one would do this: '/RE1/,/RE2/{commands;}'. Excluding
   those lines takes an extra step. To put 2 arrows before each line
   between RE1 and RE2, except for those lines:

     sed '1,/RE1/!{ /RE2/,/RE1/!s/^/>>/; }' input.fil

   The preceding script, though short, may be difficult to follow. It
   also requires that /RE1/ cannot occur on the first line of the
   input file. The following script, though it's not a one-liner, is
   easier to read and it permits /RE1/ to appear on the first line:

     # sed script to replace all lines between /RE1/ and /RE2/,
     # without matching /RE1/ or /RE2/
     /RE1/,/RE2/{
       /RE1/b
       /RE2/b
       s/^/>>/
     }
     #---end of script---

   Contents of input.fil:         Output of sed script:
      aaa                           aaa
      bbb                           bbb
      RE1                           RE1
      aaa                           >>aaa
      bbb                           >>bbb
      ccc                           >>ccc
      RE2                           RE2
      end                           end

4.25. How do I join two lines if line #1 ends in a [certain string]?

   This question appears in the section on one-line sed scripts, but
   it comes up so many times that it needs a place here also. Suppose
   a line ends with a particular string (often, a line ends with a
   backslash). How do you bring up the second line after it, even in
   cases where several consecutive lines all end in a backslash?

     sed -e :a -e '/\\$/N; s/\\\n//; ta' file   # all seds
     sed ':a; /\\$/N; s/\\\n//; ta' file        # GNU sed, ssed, HHsed

   Note that this replaces the backslash-newline with nothing. You may
   want to replace the backslash-newline with a single space instead.

4.26. How do I join two lines if line #2 begins in a [certain string]?

   The inverse situation is another FAQ. Suppose a line begins with a
   particular string. How do you bring that line up to follow the
   previous line? In this example, we want to match the string "<<="
   at the beginning of one line, bring that line up to the end of the
   line before it, and replace the string with a single space:

     sed -e :a -e '$!N;s/\n<<=/ /;ta' -e 'P;D' file   # all seds
     sed ':a; $!N;s/\n<<=/ /;ta;P;D' file             # GNU, ssed, sed15+

4.27. How do I change all paragraphs to long lines?

   A frequent request is how to convert DOS-style textfiles, in which
   each line ends with "paragraph marker", to Microsoft-style
   textfiles, in which the "paragraph" marker only appears at the end
   of real paragraphs. Sometimes this question is framed as, "How do I
   remove the hard returns at the end of each line in a paragraph?"

   The problem occurs because newer word processors don't work the
   same way older text editors did. Older text editors used a newline
   (CR/LF in DOS; LF alone in Unix) to end each line on screen or on
   disk, and used two newlines to separate paragraphs. Certain word
   processors wanted to make paragraph reformatting and reflowing work
   easily, so they use one newline to end a paragraph and never allow
   newlines _within_ a paragraph. This means that textfiles created
   with standard editors (Emacs, vi, Vedit, Boxer, etc.) appear to
   have "hard returns" at inappropriate places. The following sed
   script finds blocks of consecutive nonblank lines (i.e., paragraphs
   of text), and converts each block into one long line with one "hard
   return" at the end.

     # sed script to change all paragraphs to long lines
     /./{H; $!d;}             # Put each paragraph into hold space
     x;                       # Swap hold space and pattern space
     s/^\(\n\)\(..*\)$/\2\1/; # Move leading \n to end of PatSpace
     s/\n\(.\)/ \1/g;         # Replace all other \n with 1 space
     # Uncomment the following line to remove excess blank lines:
     # /./!d;
     #---end of sed script---

   If the input files have formatting or indentation that conveys
   special meaning (like program source code), this script will remove
   it. But if the text still needs to be extended, try 'par'
   (paragraph reformatter) or the 'fmt' utility with the -t or -c
   switches and the width option (-w) set to a number like 9999.

   SHELL AND ENVIRONMENT

4.30. How do I read environment variables with sed?

4.30.1. - on Unix platforms

   In Unix, environment variables begin with a dollar sign, such as
   $TERM, $PATH, $var or $i. In sed, the dollar sign is used to
   indicate the last line of the input file, the end of a line (in the
   LHS), or a literal symbol (in the RHS). Sed cannot access variables
   directly, so one must pay attention to shell quoting requirements
   to expand the variables properly.

   To ALLOW the Unix shell to interpret the dollar sign, put the
   script in double quotes:

     sed "s/_terminal-type_/$TERM/g" input.file >output.file

   To PREVENT the Unix shell from interpreting the dollar sign as a
   shell variable, put the script in single quotes:

     sed 's/.$//' infile >outfile

   To use BOTH Unix $environment_vars and sed /end-of-line$/ pattern
   matching, there are two solutions. (1) The easiest is to enclose
   the script in "double quotes" so the shell can see the $variables,
   and to prefix the sed metacharacter ($) with a backslash. Thus, in

     sed "s/$user\$/root/" file

   the shell interpolates $user and sed interprets \$ as the symbol
   for end-of-line.

   (2) Another method--somewhat less readable--is to concatenate the
   script with 'single quotes' where the $ should not be interpolated
   and "double quotes" where variable interpolation should occur. To
   demonstrate using the preceding script:

     sed "s/$user"'$/root/' file

   Solution #1 seems easier to remember. In either case, we search for
   the user's name (stored in a variable called $user) when it occurs
   at the end of the line ($), and substitute the word "root" in all
   matches.

   For longer shell scripts, it is sometimes useful to begin with
   single quote marks ('), close them upon encountering the variable,
   enclose the variable name in double quotes ("), and resume with
   single quotes, closing them at the end of the sed script.  Example:

     #! /bin/sh
     # sed script to illustrate 'quote'"matching"'usage'
     FROM='abcdefgh'
     TO='ABCDEFGH'
     sed -e '
     y/'"$FROM"'/'"$TO"'/;    # note the quote pairing
     # some more commands go here . . .
     # last line is a single quote mark
     '

   Thus, each variable named $FROM is replaced by $TO, and the single
   quotes are used to glue the multiple lines together in the script.
   (See also section 4.10, "How do I handle shell quoting in sed?")

4.30.2. - on MS-DOS and 4DOS platforms

   Under 4DOS and MS-DOS version 7.0 (Win95) or 7.10 (Win95 OSR2),
   environment variables can be accessed from the command prompt.
   Under MS-DOS v6.22 and below, environment variables can only be
   accessed from within batch files. Environment variables should be
   enclosed between percent signs and are case-insensitive; i.e.,
   %USER% or %user% will display the USER variable. To generate a true
   percent sign, just enter it twice.

   DOS versions of sed require that sed scripts be enclosed by double
   quote marks "..." (not single quotes!) if the script contains
   embedded tabs, spaces, redirection arrows or the vertical bar. In
   fact, if the input for sed comes from piping, a sed script should
   not contain a vertical bar, even if it is protected by double
   quotes (this seems to be bug in the normal MS-DOS syntax). Thus,

       echo blurk | sed "s/^/ |foo /"     # will cause an error
       sed "s/^/ |foo /" blurk.txt        # will work as expected

   Using DOS environment variables which contain DOS path statements
   (such as a TMP variable set to "C:\TEMP") within sed scripts is
   discouraged because sed will interpret the backslash '\' as a
   metacharacter to "quote" the next character, not as a normal
   symbol. Thus,

       sed "s/^/%TMP% /" somefile.txt

   will not prefix each line with (say) "C:\TEMP ", but will prefix
   each line with "C:TEMP "; sed will discard the backslash, which is
   probably not what you want. Other variables such as %PATH% and
   %COMSPEC% will also lose the backslash within sed scripts.

   Environment variables which do not use backslashes are usually
   workable. Thus, all the following should work without difficulty,
   if they are invoked from within DOS batch files:

       sed "s/=username=/%USER%/g" somefile.txt
       echo %FILENAME% | sed "s/\.TXT/.BAK/"
       grep -Ei "%string%" somefile.txt | sed "s/^/  /"

   while from either the DOS prompt or from within a batch file,

       sed "s/%%/ percent/g" input.fil >output.fil

   will replace each percent symbol in a file with " percent" (adding
   the leading space for readability).

4.31. How do I export or pass variables back into the environment?

4.31.1. - on Unix platforms

   Suppose that line #1, word #2 of the file 'terminals' contains a
   value to be put in your TERM environment variable. Sed cannot
   export variables directly to the shell, but it can pass strings to
   shell commands. To set a variable in the Bourne shell:

       TERM=`sed 's/^[^ ][^ ]* \([^ ][^ ]*\).*/\1/;q' terminals`;
       export TERM

   If the second word were "Wyse50", this would send the shell command
   "TERM=Wyse50".

4.31.2. - on MS-DOS or 4DOS platforms

   Sed cannot directly manipulate the environment. Under DOS, only
   batch files (.BAT) can do this, using the SET instruction, since
   they are run directly by the command shell. Under 4DOS, special
   4DOS commands (such as ESET) can also alter the environment.

   Under DOS or 4DOS, sed can select a word and pass it to the SET
   command. Suppose you want the 1st word of the 2nd line of MY.DAT
   put into an environment variable named %PHONE%. You might do this:

       @echo off
       sed -n "2 s/^\([^ ][^ ]*\) .*/SET PHONE=\1/p;3q" MY.DAT > GO_.BAT
       call GO_.BAT
       echo The environment variable for PHONE is %PHONE%
       :: cleanup
       del GO_.BAT

   The sed script assumes that the first character on the 2nd line is
   not a space and uses grouping \(...\) to save the first string of
   non-space characters as \1 for the RHS. In writing any batch files,
   make sure that output filenames such as GO_.BAT don't overwrite
   preexisting files of the same name.

4.32. How do I handle Unix shell quoting in sed?

   To embed a literal single quote (') in a script, use (a) or (b):

   (a) If possible, put the script in double quotes:

     sed "s/cannot/can't/g" file

   (b) If the script must use single quotes, then close-single-quote
   the script just before the SPECIAL single quote, prefix the single
   quote with a backslash, and use a 2nd pair of single quotes to
   finish marking the script. Thus:

     sed 's/cannot$/can'\''t/g' file

   Though this looks hard to read, it breaks down to 3 parts:

      's/cannot$/can'   \'   't/g'
      ---------------   --   -----

   To embed a literal double quote (") in a script, use (a) or (b):

   (a) If possible, put the script in single quotes. You don't need to
   prefix the double quotes with anything. Thus:

     sed 's/14"/fourteen inches/g' file

   (b) If the script must use double quotes, then prefix the SPECIAL
   double quote with a backslash (\). Thus,

     sed "s/$length\"/$length inches/g" file

   To embed a literal backslash (\) into a script, enter it twice:

     sed 's/C:\\DOS/D:\\DOS/g' config.sys

   FILES, DIRECTORIES, AND PATHS

4.40. How do I read (insert/add) a file at the top of a textfile?

   Normally, adding a "header" file to the top of a "body" file is
   done from the command prompt before passing the file on to sed.
   (MS-DOS below version 6.0 must use COPY and DEL instead of MOVE in
   the following example.)

       copy header.txt+body temp                  # MS-DOS command 1
       echo Y | move temp body                    # MS-DOS command 2
                                                    #
       cat header.txt body >temp; mv temp body    # Unix commands

   However, if inserting the file must occur within sed, there is a
   way. The sed command "1 r header.txt" will not work; it will print
   line 1 and then insert "header.txt" between lines 1 and 2. The
   following script solves this problem; however, there must be at
   least 2 lines in the target file for the script to work properly.

     # sed script to insert "header.txt" above the first line
     1{h; r header.txt
       D; }
     2{x; G; }
     #---end of sed script---

4.41. How do I make substitutions in every file in a directory, or in
      a complete directory tree?

4.41.1. - ssed and Perl solution

   The best solution for multiple files in a single directory is to
   use ssed or gsed v4.0 or higher:

     sed -i.BAK 's|foo|bar|g' files       # -i does in-place replacement

   If you don't have ssed, there is a similar solution in Perl. (Yes,
   we know this is a FAQ file for sed, not perl, but perl is more
   common than ssed for many users.)

     perl -pi.bak -e 's|foo|bar|g' files                # or
     perl -pi.bak -e 's|foo|bar|g' `find /pathname -name "filespec"`

   For each file in the filelist, sed (or Perl) renames the source
   file to "filename.bak"; the modified file gets the original
   filename. Remove '.bak' if you don't need backup copies. (Note the
   use of "s|||" instead of "s///" here, and in the scripts below. The
   vertical bars in the 's' command let you replace '/some/path' with
   '/another/path', accommodating slashes in the LHS and RHS.)

   To recurse directories in Unix or GNU/Linux:

     # We use xargs to prevent passing too many filenames to sed, but
     # this command will fail if filenames contain spaces or newlines.
     find /my/path -name '*.ht' -print | xargs sed -i.BAK 's|foo|bar|g'

   To recurse directories under Windows 2000 (CMD.EXE or COMMAND.COM):

     # This syntax isn't supported under Windows 9x COMMAND.COM
     for /R c:\my\path %f in (*.htm) do sed -i.BAK "s|foo|bar|g" %f

4.41.2. - Unix solution

   For all files in a single directory, assuming they end with *.txt
   and you have no files named "[anything].txt.bak" already, use a
   shell script:

     #! /bin/sh
     # Source files are saved as "filename.txt.bak" in case of error
     # The '&&' after cp is an additional safety feature
     for file in *.txt
     do
        cp $file $file.bak &&
        sed 's|foo|bar|g' $file.bak >$file
     done

   To do an entire directory tree, use the Unix utility find, like so
   (thanks to Jim Dennis <jadestar@rahul.net> for this script):

     #! /bin/sh
     # filename: replaceall
     # Backup files are NOT saved in this script.
     find . -type f -name '*.txt' -print | while read i
     do
        sed 's|foo|bar|g' $i > $i.tmp && mv $i.tmp $i
     done

   This previous shell script recurses through the directory tree,
   finding only files in the directory (not symbolic links, which will
   be encountered by the shell command "for file in *.txt", above). To
   preserve file permissions and make backup copies, use the 2-line cp
   routine of the earlier script instead of "sed ... && mv ...". By
   replacing the sed command 's|foo|bar|g' with something like

     sed "s|$1|$2|g" ${i}.bak > $i

   using double quotes instead of single quotes, the user can also
   employ positional parameters on the shell script command tail, thus
   reusing the script from time to time. For example,

       replaceall East West

   would modify all your *.txt files in the current directory.

4.41.3. - DOS solution:

   MS-DOS users should use two batch files like this:

      @echo off
      :: MS-DOS filename: REPLACE.BAT
      ::
      :: Create a destination directory to put the new files.
      :: Note: The next command will fail under Novel Netware
      :: below version 4.10 unless "SHOW DOTS=ON" is active.
      if not exist .\NEWFILES\NUL mkdir NEWFILES
      for %%f in (*.txt) do CALL REPL_2.BAT %%f
      echo Done!!
      :: ---End of first batch file---

      @echo off
      :: MS-DOS filename: REPL_2.BAT
      ::
      sed "s/foo/bar/g" %1 > NEWFILES\%1
      :: ---End of the second batch file---

   When finished, the current directory contains all the original
   files, and the newly-created NEWFILES subdirectory contains the
   modified *.TXT files. Do not attempt a command like

       for %%f in (*.txt) do sed "s/foo/bar/g" %%f >NEWFILES\%%f

   under any version of MS-DOS because the output filename will be
   created as a literal '%f' in the NEWFILES directory before the
   %%f is expanded to become each filename in (*.txt). This occurs
   because MS-DOS creates output filenames via redirection commands
   before it expands "for..in..do" variables.

   To recurse through an entire directory tree in MS-DOS requires a
   batch file more complex than we have room to describe. Examine the
   file SWEEP.BAT in Timo Salmi's great archive of batch tricks,
   located at <ftp://garbo.uwasa.fi/pc/link/tsbat.zip> (this file is
   regularly updated). Another alternative is to get an external
   program designed for directory recursion. Here are some recommended
   programs for directory recursion. The first one, FORALL, runs under
   either OS/2 or DOS. Unfortunately, none of these supports Win9x
   long filenames.

       http://hobbes.nmsu.edu/pub/os2/util/disk/forall72.zip
       ftp://garbo.uwasa.fi/pc/filefind/target15.zip

4.42. How do I replace "/some/UNIX/path" in a substitution?

   Technically, the normal meaning of the slash can be disabled by
   prefixing it with a backslash. Thus,

     sed 's/\/some\/UNIX\/path/\/a\/new\/path/g' files

   But this is hard to read and write. There is a better solution.
   The s/// substitution command allows '/' to be replaced by any
   other character (including spaces or alphanumerics). Thus,

     sed 's|/some/UNIX/path|/a/new/path|g' files

   and if you are using variable names in a Unix shell script,

     sed "s|$OLDPATH|$NEWPATH|g" oldfile >newfile

4.43. How do I replace "C:\SOME\DOS\PATH" in a substitution?

   For MS-DOS users, every backslash must be doubled. Thus, to replace
   "C:\SOME\DOS\PATH" with "D:\MY\NEW\PATH":

     sed "s|C:\\SOME\\DOS\\PATH|D:\\MY\\NEW\\PATH|g" infile >outfile

   Remember that DOS pathnames are not case sensitive and can appear
   in upper or lower case in the input file. If this concerns you, use
   a version of sed which can ignore case when matching (gsed, ssed,
   sedmod, sed16).

       @echo off
       :: sample MS-DOS batch file to alter path statements
       :: requires GNU sed with the /i flag for s///
       set old=C:\\SOME\\DOS\\PATH
       set new=D:\\MY\\NEW\\PATH
       gsed "s|%old%|%new%|gi" infile >outfile
       :: or
       ::     sedmod -i "s|%old%|%new%|g" infile >outfile
       set old=
       set new=

   Also, remember that under Windows long filenames may be stored in
   two formats: e.g., as "C:\Program Files" or as "C:\PROGRA~1".

4.44.  How do I emulate file-includes, using sed?

   Given an input file with file-include statements, similar to
   C-style includes or "server-side includes" (SSI) of this format:

       This is the source file. It's short.
       Its name is simply 'source'. See the script below.
       <!--#include file="ashe.inc"-->
              And this is any amount of text between
       <!--#include file="jesse.inc"-->
       This is the last line of the file.

   How do we direct sed to import/insert whichever files are at the
   point of the 'file="filename"' token? First, use this file:

     #n
     # filename: incl.sed
     # Comments supported by GNU sed or ssed. Leading '#n' should
     # be on line 1, columns 1-2 of the line.
     /<!--#include file="/ {  # For each "include file" command,
       =;                     #   print the line number
       s/^[^"]*"/{r /;        #   change pattern to 'r{ '
       s/".*//p;              #   delete rest to EOL, print
                              #   and a(ppend) a delete command
       a\
       d;}
     }
     #---end of sed script---

   Second, use the following shell script or DOS batch file (if
   running a DOS batch file, use "double quotes" instead of 'single
   quotes', and use "del" instead of "rm" to remove the temp file):

     sed -nf incl.sed source | sed 'N;N;s/\n//' >temp.sed
     sed -f temp.sed source >target
     rm temp.sed

   If you have GNU sed or ssed, you can reduce the script even further
   (thanks to Michael Carmack for the reminder):

     sed -nf incl.sed source | sed 'N;N;s/\n//' | sed -f - source >target

   In brief, the script replaces each filename with a 'r filename'
   command to insert the file at that point, while omitting the
   extraneous material. Two important things to note with this script:
   (1) There should be only one '#include file' directive per line, and
   (2) each '#include file' directive must be the *only* thing on that
   line, because everything else on the line will be deleted.

   Though the script uses GNU sed or ssed because of the great support
   for embedded script comments, it should run on any version of sed.
   If not, write me and let me know.

------------------------------

5. WHY ISN'T THIS WORKING?

5.1. Why don't my variables like $var get expanded in my sed script?

   Because your sed script uses 'single quotes' instead of "double
   quotes." Unix shells never expand $variables in single quotes.

   This is probably the most frequently-asked sed question. For more
   info on using variables, see section 4.30.

5.2. I'm using 'p' to print, but I have duplicate lines sometimes.

   Sed prints the entire file by default, so the 'p' command might
   cause the duplicate lines. If you want the whole file printed,
   try removing the 'p' from commands like 's/foo/bar/p'. If you want
   part of the file printed, run your sed script with -n flag to
   suppress normal output, and rewrite the script to get all output
   from the 'p' comand.

   If you're still getting duplicate lines, you are probably finding
   several matches for the same line. Suppose you want to print lines
   with the words "Peter" or "James" or "John", but not the same line
   twice. The following command will fail:

     sed -n '/Peter/p; /James/p; /John/p' files

   Since all 3 commands of the script are executed for each line,
   you'll get extra lines. A better way is to use the 'd' (delete) or
   'b' (branch) commands, like so (with GNU sed):

     sed '/Peter/b; /James/b; /John/b; d' files          # one way
     sed -n '/Peter/{p;d;};/James/{p;d;};/John/p' files  # a 2nd way
     sed -n '/Peter/{p;b;};/James/{p;b;};/John/p' files  # a 3rd way
     sed '/Peter\|James\|John/!d' files                  # shortest way

   On standard seds, these must be broken down with -e commands:

     sed -e '/Peter/b' -e '/James/b' -e '/John/b' -e d files
     sed -n -e '/Peter/{p;d;}' -e '/James/{p;d;}' -e '/John/p' files

   The 3rd line would require too many -e commands to fit on one line,
   since standard versions of sed require an -e command after each 'b'
   and also after each closing brace '}'.

5.3. Why does my DOS version of sed process a file part-way through
     and then quit?

   First, look for errors in the script. Have you used the -n switch
   without telling sed to print anything to the console? Have you read
   the docs to your version of sed to see if it has a syntax you may
   have misused? (Look for an N or H command that gathers too much.)

   Next, if you are sure your sed script is valid, a probable cause is
   an end-of-file marker embedded in the file. An EOF marker (SUB) is
   a Control-Z character, with the value of 1A hex (26 decimal). As
   soon as any DOS version of sed encounters a Ctrl-Z character, sed
   stops processing.

   To locate the EOF character, use Vern Buerg's shareware file viewer
   LIST.COM <http://www.buerg.com/list.html>. In text mode, look for a
   right-arrow symbol; in hex mode (Alt-H), look for a 1A code. With
   Unix utilities ported to DOS, use 'od' (octal dump) to display
   hexcodes in your file, and then use sed to locate the offending
   character:

       od -txC badfile.txt | sed -n "/ 1a /p; / 1a$/p"

   Then edit the input file to remove the offending character(s).

   If you would rather NOT edit the input file, there is still a fix.
   It requires the DJGPP 32-bit port of 'tr', the Unix translate
   program (v1.22 or higher). GNU od and tr are currently at v2.0 (for
   DOS); they are packaged with the GNU text utilities, available at

       ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/txt20b.zip
       http://www.simtel.net/gnudlpage.php?product=/gnu/djgpp/v2gnu/txt20b.zip&name=txt20b.zip

   It is important to get the DJGPP version of 'tr' because other
   versions ported to DOS will stop processing when they encounter the
   EOF character. Use the -d (delete) command:

       tr -d \32 < badfile.txt | sed -f myscript.sed

5.4. My RE isn't matching/deleting what I want it to. (Or, "Greedy vs.
     stingy pattern matching")

   The two most common causes for this problem are: (1) misusing the
   '.' metacharacter, and (2) misusing the '*' metacharacter. The RE
   '.*' is designed to be "greedy" (i.e., matching as many characters
   as possible). However, sometimes users need an expression which is
   "stingy," matching the shortest possible string.

   (1) On single-line patterns, the '.' metacharacter matches any
   single character on the line. ('.' cannot match the newline at the
   end of the line because the newline is removed when the line is put
   into the pattern space; sed adds a newline automatically when the
   pattern space is printed.) On multi-line patterns obtained with the
   'N' or 'G' commands, '.' _will_ match a newline in the middle of the
   pattern space. If there are 3 lines in the pattern space, "s/.*//"
   will delete all 3 lines, not just the first one (leaving 1 blank
   line, since the trailing newline is added to the output).

   Normal misuse of '.' occurs in trying to match a word or bounded
   field, and forgetting that '.' will also cross the field limits.
   Suppose you want to delete the first word in braces:

       echo {one} {two} {three} | sed 's/{.*}/{}/'       # fails
       echo {one} {two} {three} | sed 's/{[^}]*}/{}/'    # succeeds

   's/{.*}/{}/' is not the solution, since the regex '.' will match
   any character, including the close braces. Replace the '.' with
   '[^}]', which signifies a negated character set '[^...]' containing
   anything other than a right brace. FWIW, we know that 's/{one}/{}/'
   would also solve our question, but we're trying to illustrate the
   use of the negated character set: [^anything-but-this].

   A negated character set should be used for matching words between
   quote marks, for fields separated by commas, and so on. See also
   section 4.12 ("How do I parse a comma-delimited data file?").

   (2) The '*' metacharacter represents zero or more instances of the
   previous expression. The '*' metacharacter looks for the leftmost
   possible match first and will match zero characters. Thus,

       echo foo | sed 's/o*/EEE/'

   will generate 'EEEfoo', not 'fEEE' as one might expect. This is
   because /o*/ matches the null string at the beginning of the word.

   After finding the leftmost possible match, the '*' is GREEDY; it
   always tries to match the longest possible string. When two or
   three instances of '.*' occur in the same RE, the leftmost instance
   will grab the most characters. Consider this example, which uses
   grouping '\(...\)' to save patterns:

       echo bar bat bay bet bit | sed 's/^.*\(b.*\)/\1/'

   What will be displayed is 'bit', never anything longer, because the
   leftmost '.*' took the longest possible match. Remember this rule:
   "leftmost match, longest possible string, zero also matches."

5.5. What is CSDPMI*B.ZIP and why do I need it?

   If you use MS-DOS outside of Windows and try to use GNU sed v1.18
   or 3.02, you may encounter the following error message:

       no DPMI - Get csdpmi*b.zip

   "DPMI" stands for DOS Protected Mode Interface; it's basically a
   means of running DOS in Protected Mode (as opposed to Real Mode),
   which allows programs to share resources in extended memory without
   conflicting with one another. Running HIMEM.SYS and EMM386.EXE is
   not enough. The "CSDPMI*B.ZIP" refers to files written by Charles
   Sandmann to provide DPMI services for 32-bit computers (i.e.,
   386SX, 386DX, 486SX, etc.). Download the binary file (the source
   code is also available):

       http://www.delorie.com/djgpp/dl/ofc/simtel/v2misc/csdpmi5b.zip  # binaries
       http://www.delorie.com/djgpp/dl/ofc/simtel/v2misc/csdpmi5s.zip  # source
       ftp://ftp.cdrom.com/pub/simtelnet/gnu/djgpp/v2misc/csdpmi5b.zip # binaries
       ftp://ftp.cdrom.com/pub/simtelnet/gnu/djgpp/v2misc/csdpmi5s.zip # source

   and extract CWSDPMI.EXE, CWSDPR0.EXE and CWSPARAM.EXE from the ZIP
   file. Put all 3 CWS*.EXE files in the same directory as GSED.EXE
   and you're all set. There are DOC files enclosed, but they're
   nearly incomprehensible for the average computer user. (Another
   case of user-vicious documentation.)

   If you're running Windows and you normally use a DOS session to run
   GNU sed (i.e., you get to a DOS prompt with a resizable window or
   you press Alt-Enter to switch to full-screen mode), you don't need
   the CWS*.EXE files at all, since Windows uses DPMI already.

5.6. Where are the man pages for GNU sed?

   Prior to GNU sed v3.02, there weren't any. Until recently, man
   pages distributed with gsed were borrowed from old sources or from
   other compilations. None of them were "official." GNU sed v3.02 had
   the first real set of official man pages, and the documentation has
   greatly improved with GNU sed version 4.0, which now includes both
   man pages and textinfo pages.

5.7. How do I tell what version of sed I am using?

   Try entering "sed" all by itself on the command line, followed by
   no arguments or parameters.  Also, try "sed --version".  In a
   pinch, you can also try this:

       strings sed | grep -i ver

   Your version of 'strings' must be a version of the Unix utility of
   this name. It should not be the DOS utility STRINGS.COM by Douglas
   Boling.

5.8. Does sed issue an exit code?

   Most versions of sed do not, but check the documentation that came
   with whichever version you are using. GNU sed issues an exit code
   of 0 if the program terminated normally, 1 if there were errors in
   the script, and 2 if there were errors during script execution.

5.9. The 'r' command isn't inserting the file into the text.

   On most versions of sed (but not all), the 'r' (read) and 'w'
   (write) commands must be followed by exactly one space, then the
   filename, and then terminated by a newline. Any additional
   characters before or after the filename are interpreted as *part*
   of the filename. Thus

       /RE/r  insert.me

   will would try to locate a file called ' insert.me' (note the
   leading space!). If the file was not found, most versions of sed
   say nothing, not even an error message.

   When sed scripts are used on the command line, every 'r' and 'w'
   must be the last command in that part of the script. Thus,

       sed -e '/regex/{r insert.file;d;}' source         # will fail
       sed -e '/regex/{r insert.file' -e 'd;}' source    # will succeed

5.10. Why can't I match or delete a newline using the \n escape sequence?
      Why can't I match 2 or more lines using \n?

   The \n will never match the newline at the end-of-line because the
   newline is always stripped off before the line is placed into the
   pattern space. To get 2 or more lines into the pattern space, use
   the 'N' command or something similar (such as 'H;...;g;').

   Sed works like this: sed reads one line at a time, chops off the
   terminating newline, puts what is left into the pattern space where
   the sed script can address or change it, and when the pattern space
   is printed, appends a newline to stdout (or to a file). If the
   pattern space is entirely or partially deleted with 'd' or 'D', the
   newline is *not* added in such cases. Thus, scripts like

       sed 's/\n//' file       # to delete newlines from each line
       sed 's/\n/foo\n/' file  # to add a word to the end of each line

   will _never_ work, because the trailing newline is removed _before_
   the line is put into the pattern space. To perform the above tasks,
   use one of these scripts instead:

       tr -d '\n' < file              # use tr to delete newlines
       sed ':a;N;$!ba;s/\n//g' file   # GNU sed to delete newlines
       sed 's/$/ foo/' file           # add "foo" to end of each line

   Since versions of sed other than GNU sed have limits to the size of
   the pattern buffer, the Unix 'tr' utility is to be preferred here.
   If the last line of the file contains a newline, GNU sed will add
   that newline to the output but delete all others, whereas tr will
   delete all newlines.

   To match a block of two or more lines, there are 3 basic choices:
   (1) use the 'N' command to add the Next line to the pattern space;
   (2) use the 'H' command at least twice to append the current line
   to the Hold space, and then retrieve the lines from the hold space
   with x, g, or G; or (3) use address ranges (see section 3.3, above)
   to match lines between two specified addresses.

   Choices (1) and (2) will put an \n into the pattern space, where it
   can be addressed as desired ('s/ABC\nXYZ/alphabet/g'). One example
   of using 'N' to delete a block of lines appears in section 4.13
   ("How do I delete a block of _specific_ consecutive lines?"). This
   example can be modified by changing the delete command to something
   else, like 'p' (print), 'i' (insert), 'c' (change), 'a' (append),
   or 's' (substitute).

   Choice (3) will not put an \n into the pattern space, but it _does_
   match a block of consecutive lines, so it may be that you don't
   even need the \n to find what you're looking for. Since several
   versions of sed support this syntax:

       sed '/start/,+4d'  # to delete "start" plus the next 4 lines,

   in addition to the traditional '/from here/,/to there/{...}' range
   addresses, it may be possible to avoid the use of \n entirely.

5.11. My script aborts with an error message, "event not found".

   This error is generated by the csh or tcsh shells, not by sed. The
   exclamation mark (!) is special to csh/tcsh, and if you use it in
   command-line or shell scripts--even within single quotes--it must
   be preceded by a backslash. Thus, under the csh/tcsh shell:

       sed '/regex/!d'      # will fail
       sed '/regex/\!d'     # will succeed

   The exclamation mark should not be prefixed with a backslash when
   the script is called from a file, as "-f script.file".

------------------------------

6. OTHER ISSUES

6.1. I have a certain problem that stumps me. Where can I get help?

   Post your question on the "sed-users" mailing list (section 2.3.2),
   where many sed users will be able to see your question. You will have
   to subscribe to have posting privileges.

   Your other alternative is one of these newsgroups:

      - alt.comp.editors.batch
      - comp.editors
      - comp.unix.questions
      - comp.unix.shell

6.2. How does sed compare with awk, perl, and other utilities?

   Awk is a much richer language with many features of a programming
   language, including variable names, math functions, arrays, system
   calls, etc. Its command structure is similar to sed:

      address { command(s) }

   which means that for each line or range of lines that matches the
   address, execute the command(s). In both sed and awk, an address
   can be a line number or a RE somewhere on the line, or both.

   In program size, awk is 3-10 times larger than sed. Awk has most of
   the functions of sed, but not all. Notably, sed supports
   backreferences (\1, \2, ...) to previous expressions, and awk does
   not have any comparable syntax. (One exception: GNU awk v3.0
   introduced gensub(), which supports backreferences only on
   substitutions.)

   Perl is a general-purpose programming language, with many features
   beyond text processing and interprocess communication, taking it
   well past awk or other scripting languages. Perl supports every
   feature sed does and has its own set of extended regular
   expressions, which give it extensive power in pattern matching and
   processing. (Note: the standard perl distribution comes with 's2p',
   a sed-to-perl conversion script. See section 3.6 for more info.)
   Like sed and awk, perl scripts do not need to be compiled into
   binary code. Like sed, perl can also run many useful "one-liners"
   from the command line, though with greater flexibility; see
   question 4.41 ("How do I make substitutions in every file in a
   directory, or in a complete directory tree?").

   On the other hand, the current version of perl is from 8 to 35
   times larger than sed in its executables alone (perl's library
   modules and allied files not included!). Further, for most simple
   tasks such as substitution, sed executes more quickly than either
   perl or awk. All these utilities serve to process input text,
   transforming it to meet our needs . . . or our arbitrary whims.

6.3. When should I use sed?

   When you need a small, fast program to modify words, lines, or
   blocks of lines in a textfile.

6.4. When should I NOT use sed?

   You should not use sed when you have "dedicated" tools which can do
   the job faster or with an easier syntax. Do not use sed when you
   only want to:

   - print individual lines, based on patterns within the line itself.
     Instead, use "grep".

   - print blocks of lines, with 1 or more lines of context above or
     below a specific regular expression. Instead, use the GNU version
     of grep as follows:

        grep -A{number} -B{number} "regex"

   - remove individual lines, based on patterns within the line
     itself. Instead, use "grep -v".

   - print line numbers.  Instead, use "nl" or "cat -n".

   - reformat lines or paragraphs. Instead, use "fold", "fmt" or "par".

   The tr utility is also more suited than sed to some simple tasks. For
   example, to:

   - delete individual characters. Instead of "s/[a-d]//g", use

        tr -d "[a-d]"

   - squeeze sequential characters. Instead of "s/ee*/e/g", use

        tr -s "{character-set}"

   - change individual characters. Instead of "y/abcdef/ABCDEF/", use

        tr "[a-f]" "[A-F]"

   Note, however, that tr does not support giving input files on the
   command line, so the syntax is:

     tr {options-and-patterns} < input-file

   or, to process multiple files:

     cat input-file1 input-file2 | tr {options-and-patterns}

   If you have multiple files, using tr instead of sed is often more of
   an exercise than a useful thing. Although sed can perfectly emulate
   certain functions of cat, grep, nl, rev, sort, tac, tail, tr, uniq,
   and other utilities, producing identical output, the native utilities
   are usually optimized to do the job more quickly than sed.

6.5. When should I ignore sed and use awk or Perl instead?

   If you can write the same script in awk or Perl and do it in less
   time, then use Perl or awk. There's no reason to spend an hour
   writing and debugging a sed script if you can do it in Perl in 10
   minutes (assuming that you know Perl already) and if the processing
   time or memory use is not a factor. Don't hunt pheasants with a .22
   if you have a shotgun at your side . . . unless you simply enjoy
   the challenge!

   Specifically, use awk or perl if you need to:

      - count fields or words on a line. (awk)
      - count lines in a block or objects in a file.
      - check lengths of strings or do math operations.
      - handle very long lines or need very large buffers. (or gsed)
      - handle binary data (control characters). (perl: binmode)
      - loop through an array or list.
      - test for file existence, filesize, or fileage.
      - treat each paragraph as a line. (well, not always)

6.6. Known limitations among sed versions

   Limits on distributed versions, although source code for most
   versions of free sed allows for modification and recompilation. As
   used below, "no limit" means there is no "fixed" limit. Limits are
   actually determined by one's hardware, memory, operating system,
   and which C library is used to compile sed.

6.6.1. Maximum line length

      GNU sed:        no limit
      ssed:           no limit
      sedmod v1.0:    4096 bytes
      HHsed v1.5:     4000 bytes
      sed v1.6:       [pending]

6.6.2. Maximum size for all buffers (pattern space + hold space)

      GNU sed:        no limit
      ssed:           no limit
      sedmod v1.0:    4096 bytes
      HHsed v1.5:     4000 bytes
      sed v1.6:       [pending]

6.6.3. Maximum number of files that can be read with read command

      GNU sed v3+:    no limit
      ssed:           no limit
      GNU sed v2.05:  total no. of r and w commands may not exceed 32
      sedmod v1.0:    total no. of r and w commands may not exceed 20
      sed v1.6:       [pending]

6.6.4. Maximum number of files that can be written with 'w' command

      GNU sed v3+:    no limit (but typical Unix is 253)
      ssed:           no limit (but typical Unix is 253)
      GNU sed v2.05:  total no. of r and w commands may not exceed 32
      sedmod v1.0:    10
      HHsed v1.5:     10
      sed v1.6:       [pending]

6.6.5. Limits on length of label names

      GNU sed:        no limit
      ssed:           no limit
      HHsed v1.5:     no limit
      sed v1.6:       [pending]
      BSD sed:        8 characters

   Note that GNU sed and ssed both consider a semicolon to terminate a
   label name.

6.6.6. Limits on length of write-file names

      GNU sed:        no limit
      ssed:           no limit
      HHsed v1.5:     no limit
      sed v1.6:       [pending]
      BSD sed:        40 characters

6.6.7. Limits on branch/jump commands

      GNU sed:        no limit
      ssed:           no limit
      HHsed v1.5:     50
      sed v1.6:       [pending]

   As a practical consequence, this means that HHsed will not read
   more than 50 lines into the pattern space via an N command, even if
   the pattern space is only a few hundred bytes in size. HHsed exits
   with an error message, "infinite branch loop at line {nn}".

6.7. Known incompatibilities between sed versions

6.7.1. Issuing commands from the command line

   Most versions of sed permit multiple commands to issued on the
   command line, separated by a semicolon (;). Thus,

       sed 'G;G' file

   should triple-space a file. However, for non-GNU sed, some commands
   *require* separate expressions on the command line. These include:

      - all labels (':a', ':more', etc.)
      - all branching instructions ('b', 't')
      - commands to read and write files ('r' and 'w')
      - any closing brace, '}'

   If these commands are used, they must be the LAST commands of an
   expression. Subsequent commands must use another expression
   (another -e switch plus arguments).  E.g.,

     sed  -e :a -e 's/^.\{1,77\}$/ &/;ta' -e 's/\( *\)\1/\1/' files

   GNU sed, ssed, sed15 and sed16 all permit these commands to be
   followed by a semicolon, so the previous script can be written:

     sed  ':a;s/^.\{1,77\}$/ &/;ta;s/\( *\)\1/\1/' files

   Versions differ in implementing the 'a' (append), 'c' (change), and
   'i' (insert) commands:

      sed "/foo/i New text here"              # HHsed/sedmod/gsed-30280
      gsed -e "/foo/i\\" -e "New text here"   # GNU sed
      sed1 -e "/foo/i" -e "New text here"     # one version of sed
      sed2 "/foo/i\ New text here"            # another version

6.7.2. Using comments (prefixed by the '#' sign)

   Most versions of sed permit comments to appear in sed scripts only
   on the first line of the script. Comments on line 2 or thereafter
   are not recognized and will generate an error like "unrecognized
   command" or "command [bad-line-here] has trailing garbage".

   GNU sed, HHsed, sedmod, and HP-UX sed permit comments to appear on
   any line of the script, except after labels and branching commands
   (b,t), *provided* that a semicolon (;) occurs after the command
   itself. This syntax makes sed similar to awk and perl, which use a
   similar commenting structure in their scripts.  Thus,

      # GNU style sed script
      $!N;                        # except for last line, get next line
      s/^\([0-9]\{5\}\).*\n\1.*//;    # if first 5 digits of each line
                                      # match, delete BOTH lines.
      t skip
      P;                              # print 1st line only if no match
      :skip
      D;                    # delete 1st line of pattern space and loop
      #---end of script---

   is a valid script for GNU-based versions of sed, but is
   unrecognized for most other versions of sed.

   Finally, if the first two characters in a disk file script are
   "#n", the output is suppressed, exactly as if -n were entered on
   the command line. This is true for the following versions of sed:

      - ssed v3.57 and above
      - gsed
      - HHsed v1.5
      - sed v1.6

   This syntax is not recognized by these versions of sed:

      - ssed v3.45 to v3.50 (other versions untested)
      - sedmod v1.0

6.7.3. Special syntax in REs

A. HHsed v1.5 (by Howard Helman)

   The following expressions can be used for /RE/ addresses or in the
   LHS side of a substitution:

      +    - 1 or more occurrences of previous RE: same as \{1,\}
      \<   - boundary between nonword and word character
      \>   - boundary between word and nonword character

   The following expressions can be used for /RE/ addresses or on
   either side of a substitution:

      \a   - bell         (ASCII 07, 0x07)
      \b   - backspace    (ASCII 08, 0x08)
      \e   - escape       (ASCII 27, 0x1B)
      \f   - formfeed     (ASCII 12, 0x0C)
      \n   - newline      (printed as 2 bytes, 0D 0A or ^M^J, in DOS)
      \r   - return       (ASCII 13, 0x0D)
      \t   - tab          (ASCII 09, 0x09)
      \v   - vertical tab (ASCII 11, 0x0B)
      \xHH - the ASCII character corresponding to 2 hex digits HH.

B. sed v1.6 (by Walter Briscoe)

   sed v1.6 accepts every expression supported by sed v1.5 (above),
   plus the following elements, which can also used in the RHS of a
   substitution (in addition to those listed above):

      \\~  - insert replacement pattern defined in last s/// command
             (must be used alone in the RHS)
      \l   - change next element to lower case
      \L   - change remaining elements to lower case
      \u   - change next element to upper case
      \U   - change remaining elements to upper case
      \e   - end case conversion of next element
      \E   - end case conversion of remaining elements
      $0   - insert pattern space BEFORE the substitution
      $1-$9 - match Nth word on the pattern space


C. sedmod v1.0 (by Hern Chen)

   The following expressions can be used for /RE/ addresses in the LHS
   of a substitution:

      +    - 1 or more occurrences of previous RE: same as \{1,\}
      \a   - any alphanumeric: same as [a-zA-Z0-9]
      \A   - 1 or more alphas: same as \a+
      \d   - any digit: same as [0-9]
      \D   - 1 or more digits: same as \d+
      \h   - any hex digit: same as [0-9a-fA-F]
      \H   - 1 or more hexdigits: same as \h+
      \l   - any letter: same as [A-Za-z]
      \L   - 1 or more letters: same as \l+
      \n   - newline      (read as 2 bytes, 0D 0A or ^M^J, in DOS)
      \s   - any whitespace character: space, tab, or vertical tab
      \S   - 1 or more whitespace chars: same as \s+
      \t   - tab          (ASCII 09, 0x09)
      \<   - boundary between nonword and word character
      \>   - boundary between word and nonword character

   The following expressions can be used in the RHS of a substitution.
   "Elements" refer to \1 .. \9, &, $0, or $1 .. $9:

      &    - insert regexp defined on LHS
      \e   - end case conversion of next element
      \E   - end case conversion of remaining elements
      \l   - change next element to lower case
      \L   - change remaining elements to lower case
      \n   - newline      (printed as 2 bytes, 0D 0A or ^M^J, in DOS)
      \t   - tab          (ASCII 09, 0x09)
      \u   - change next element to upper case
      \U   - change remaining elements to upper case
      $0   - insert the original pattern space
      $1-$9 - match Nth word on the pattern space

D. UnixDos sed

   The following expressions can be used in text, LHS, and RHS:

      \n   - newline      (printed as 2 bytes, 0D 0A or ^M^J, in DOS)

E. GNU sed v1.03 (by Frank Whaley)

   When used with the -x (extended) switch on the command line, or
   when '#x' occurs as the first line of a script, Whaley's gsed103
   supports the following expressions in both the LHS and RHS of a
   substitution:

      \|      matches the expression on either side
      ?       0 or 1 occurrences of previous RE: same as \{0,1\}
      +       1 or more occurrence of previous RE: same as \{1,\}
      \a      "alert" beep     (BEL, Ctrl-G, 0x07)
      \b      backspace        (BS, Ctrl-H, 0x08)
      \f      formfeed         (FF, Ctrl-L, 0x0C)
      \n      newline          (LF, Ctrl-J, 0x0A)
      \r      carriage-return  (CR, Ctrl-M, 0x0D)
      \t      horizontal tab   (HT, Ctrl-I, 0x09)
      \v      vertical tab     (VT, Ctrl-K, 0x0B)
      \bBBB   binary char, where BBB are 1-8 binary digits, [0-1]
      \dDDD   decimal char, where DDD are 1-3 decimal digits, [0-9]
      \oOOO   octal char, where OOO are 1-3 octal digits, [0-7]
      \xHH    hex char, where HH are 1-2 hex digits, [0-9A-F]

   In normal mode, with or without the -x switch, the following escape
   sequences are also supported in regex addressing or in the LHS of a
   substitution:

      \`      matches beginning of pattern space: same as /^/
      \'      matches end of pattern space: same as /$/
      \B      boundary between 2 word or 2 nonword characters
      \w      any nonword character [*BUG!* should be a word char]
      \W      any nonword character: same as /[^A-Za-z0-9]/
      \<      boundary between nonword and word char
      \>      boundary between word and nonword char

F. GNU sed v2.05 and higher versions

   The following expressions can be used for /RE/ addresses or in the
   LHS side of a substitution:

      \`  - matches the beginning of the pattern space (same as "^")
      \'  - matches the end of the pattern space (same as "$")
      \?  - 0 or 1 occurrence of previous character: same as \{0,1\}
      \+  - 1 or more occurrences of previous character: same as \{1,\}
      \|  - matches the string on either side, e.g., foo\|bar
      \b  - boundary between word and nonword chars (reversible)
      \B  - boundary between 2 word or between 2 nonword chars
      \n  - embedded newline (usable after N, G, or similar commands)
      \w  - any word character: [A-Za-z0-9_]
      \W  - any nonword char: [^A-Za-z0-9_]
      \<  - boundary between nonword and word character
      \>  - boundary between word and nonword character

   On \b, \B, \<, and \>, see section 6.7.4 ("Word boundaries"),
   below.

   Undocumented -r switch:

   Beginning with version 3.02, GNU sed has an undocumented -r switch
   (undocumented till version 4.0), activating Extended Regular
   Expressions in the following manner:

       ?      -  0 or 1 occurrence of previous character
       +      -  1 or more occurrences of previous character
       |      -  matches the string on either side, e.g., foo|bar
       (...)  -  enable grouping without backslash
       {...}  -  enable interval expression without backslash

   When the -r switch (mnemonic: "regular expression") is used, prefix
   these symbols with a backslash to disable the special meaning.

   Escape sequences:

   Beginning with version 3.02.80, the following escape sequences can
   now be used on both sides of a "s///" substitution:

      \a      "alert" beep     (BEL, Ctrl-G, 0x07)
      \f      formfeed         (FF, Ctrl-L, 0x0C)
      \n      newline          (LF, Ctrl-J, 0x0A)
      \r      carriage-return  (CR, Ctrl-M, 0x0D)
      \t      horizontal tab   (HT, Ctrl-I, 0x09)
      \v      vertical tab     (VT, Ctrl-K, 0x0B)
      \oNNN   a character with the octal value NNN
      \dNNN   a character with the decimal value NNN
      \xHH    a character with the hexadecimal value HH

   Note that GNU sed also supports "character classes", a POSIX
   extension to regexes, described in section 3.7, above.

G. sed 4.0 and higher versions

   The following expressions can be used in the RHS of a substitution.

      \e   - end case conversion
      \l   - change next character to lower case
      \L   - change remaining text to lower case
      \n   - newline      (printed as 2 bytes, 0D 0A or ^M^J, in DOS)
      \t   - tab          (ASCII 09, 0x09)
      \u   - change next character to upper case
      \U   - change remaining text to upper case

   In addition, GNU sed 4.0 can modify the way ^ and $ are interpreted,
   so that ^ can also match an empty string after a newline character,
   and $ can also match an empty string before a newline character (to
   do this, add an "M" after the regular expression terminator, like
   /^>/M -- see section 3.1.1). Even if you use this feature, \` and \'
   still match the beginning and the end of the pattern space,
   respectively.

H. ssed

   Everything that was said for GNU sed applies to ssed as well. In
   addition, in Perl-mode (-R switch), these become active or inactive:

      .     - no longer matches new-line characters
      \A    - matches beginning of pattern space
      \Z    - matches end of pattern space or last newline in the PS
      \z    - matches end of pattern space
      \d    - matches any digit: same as [0-9]
      \D    - matches any non-digit: same as [^0-9]
      \`    - no longer matches beginning of pattern space
      \'    - no longer matches end of pattern space
      \<    - no longer matches boundary between nonword & word char
      \>    - no longer matches boundary between word & nonword char
      \oNNN - no longer matches char with octal value NNN
      \dNNN - no longer matches char with decimal value NNN
      \NNN  - matches char with octal value NNN

   Perl mode supports lookahead (?=match) and lookbehind (?<=match)
   pattern matching.  The matched text is NOT captured in "&" for s///
   replacements!

      foo(?=bar)   - match "foo" only if "bar" follows it
      foo(?!bar)   - match "foo" only if "bar" does NOT follow it
      (?<=foo)bar  - match "bar" only if "foo" precedes it
      (?<!foo)bar  - match "bar" only if "foo" does NOT precede it

      (?<!in|on|at)foo
                  - match "foo" only if NOT preceded by "in", "on" or "at"
      (?<=\d{3})(?<!999)foo
                  - match "foo" only if preceded by 3 digits other than "999"

  In Perl mode, there are two new switches in /addressing/ or s///
  commands. Switches may be lowercase in s/// commands, but must be
  uppercase in /addressing/:

       /S  - lets "." match a newline also
       /X  - extra whitespace is ignored. See below, for sample usage.

   Here are some examples of Perl-style regular expressions. Use the -R
   switch.

     (?i)abc    - case-insensitive match of abc, ABC, aBc, ABc, etc.
     ab(?i)c    - same as above; the (?i) applies throughout the pattern
     (ab(?i)c)  - matches abc or abC; the outer parens make the difference!
     (?m)       - multi-line pattern space: same as "s/FIND/REPL/M"
     (?s)       - set "." to match newline also: same as "s/FIND/REPL/S"
     (?x)       - ignore whitespace and #comments; see section (9) below.

     (?:abc)foo    - match "abcfoo", but do not capture 'abc' in \1
     (?:ab|cd)ef   - match "abef" or "cdef"; only 'cd' is captured in \1
     (?#remark)xy  - match "xy"; remarks after "#" are ignored.

   And here are some sample uses of /X switch to add comments to complex
   expressions. To embed literal spaces, precede with \ or put inside
   [brackets].

     # ssed script to change "(123) 456-7890" into "[ac123] 456-7890"
     #
     s/ # BACKSLASH IS NEEDED AT END OF EACH LINE!   \
     \(                   # literal left paren, (    \
     (\d{3})              # 3 digits                 \
     \)                   # literal right paren, )   \
     [ \t]*               # zero or more spaces or tabs  \
     (\d{3}-\d{4})        # 3 digits, hyphen, 4 digits   \
     /[ac\1] \2/gx;       # replace g(lobally), with e(x)tended spacing

6.7.4. Word boundaries

   GNU sed, ssed, sed16, sed15 and sedmod use certain symbols to define
   the boundary between a "word character" and a nonword character. A
   word character fits the regex "[A-Za-z0-9_]". Note: a word character
   includes the underscore "_" but not the hyphen, probably because the
   underscore is permissible as a label in sed and in other scripting
   languages. (In gsed103, a word character did NOT include the
   underscore; it included alphanumerics only.)

   These symbols include '\<' and '\>' (gsed, ssed, sed15, sed16,
   sedmod) and '\b' and '\B' (gsed only). Note that the boundary
   symbols do not represent a character, but a position on the line.
   Word boundaries are used with literal characters or character sets
   to let you match (and delete or alter) whole words without
   affecting the spaces or punctuation marks outside of those words.
   They can only be used in a "/pattern/" address or in the LHS of a
   's/LHS/RHS/' command. The following table shows how these symbols
   may be used in HHsed and GNU sed. Sedmod matches the syntax of
   HHsed.

      Match position      Possible word boundaries   HHsed   GNU sed
      ---------------------------------------------------------------
      start of word    [nonword char]^[word char]      \<    \< or \b
      end of word         [word char]^[nonword char]   \>    \> or \b
      middle of word      [word char]^[word char]     none      \B
      outside of word  [nonword char]^[nonword char]  none      \B
      ---------------------------------------------------------------

   In ssed, the symbols '\<' and '\>' lose their special meaning when
   the -R switch is used to invoke Perl-style expressions. However,
   the identical meaning of '\<' and '\>' can be obtained through
   these nonmatching, zero-width assertions:

       (?<!\w)(?=\w)  and   (?<=\w)(?!\w)

6.7.5. Commands which operate differently

A. GNU sed version 3.02 and 3.02.80

   The N command no longer discards the contents of the pattern space
   upon reaching the end of file. This is not a bug, it's a feature.
   However, it breaks certain scripts which relied on the older
   behavior of N.

   'N' adds the Next line to the pattern space, enabling multiple
   lines to be stored and acted upon. Upon reaching the last line of
   the file, if the N command was issued again, the contents of the
   pattern space would be silently deleted and the script would abort
   (this has been the traditional behavior). For this reason, sed
   users generally wrote:

       $!N;   # to add the Next line to every line but the last one.

   However, certain sed scripts relied on this behavior, such as the
   script to delete trailing blank lines at the end of a file (see
   script #12 in section 3.2, "Common one-line sed scripts", above).
   Also, classic textbooks such as Dale Dougherty and Arnold Robbins'
   _sed & awk_ documented the older behavior.

   The GNU sed maintainer felt that despite the portability problems
   this would cause, changing the N command to print (rather than
   delete) the pattern space was more consistent with one's intuitions
   about how a command to "append the Next line" _ought_ to behave.
   Another fact favoring the change was that "{N;command;}" will
   delete the last line if the file has an odd number of lines, but
   print the last line if the file has an even number of lines.

   To convert scripts which used the former behavior of N (deleting
   the pattern space upon reaching the EOF) to scripts compatible with
   all versions of sed, change a lone "N;" to "$d;N;".

------------------------------

7. KNOWN BUGS AMONG SED VERSIONS

   Most versions of GNU sed and ssed contain a "buglist" in the
   archive source code of known errors or reported behaviors that may
   be misconstrued as bugs. This portion of the sed FAQ does _not_
   attempt to fully reproduce those buglists files. However, we do
   seek to do some substantial reporting, particularly where certain
   programs have no "buglist" of their own or are not being actively
   maintained.

   As a rule of thumb, if the bug "bites" someone on the sed-users
   mailing list, I tend to report it.

7.1. ssed v3.59 (by Paolo Bonzini)

   (1) N does not discard the contents of the pattern space upon
   reaching the end of file; not a bug. See section 6.7.5.A, above.

   (2) If \x26 is entered into the RHS of a substitution, it is
   interpreted as an ampersand metacharacter, and the entire pattern
   matched in the "find" portion is inserted at that point. A literal
   ampersand should be inserted instead.

   (3) Under Windows 2000, the -i switch doesn't create backup files
   properly. When passed one or more files to process, the source
   file(s) are unchanged, and the output changed files are given
   filenames like sedDOSxyz with no way to correspond them with the
   names of the source files.

7.2. GNU sed v4.0 - v4.0.5

   (1) N does not discard the contents of the pattern space upon
   reaching the end of file; not a bug. See section 6.7.5.A, above.

   (2) If \x26 is entered into the RHS of a substitution, it is
   interpreted as an ampersand metacharacter, and the entire pattern
   matched in the "find" portion is inserted at that point. A literal
   ampersand should be inserted instead.

7.3. GNU sed v3.02.80

   (1) N does not discard the contents of the pattern space upon
   reaching the end of file; not a bug. See section 6.7.5.A, above.

   (2) Same as #2 for GNU sed v4.0, above.

7.4. GNU sed v3.02

   (1) Affects only v3.02 binaries compiled with DJGPP for MS-DOS and
   MS-Windows: 'l' (list) command does not display a lone carriage
   return (0x0D, ^M) embedded in a line.

   (2) The expression "\<" causes problems when attempting the
   following types of substitutions, which should print "+aaa +bbb":

       echo aaa bbb | sed 's/\</+/g'    # prints "+a+a+a +b+b+b"
       echo aaa bbb | sed 's/\<./+&/g'  # prints "+a+a+a +b+b+b"

   (3) The N command no longer discards the contents of the pattern
   space upon reaching the end of file. This is not a bug, it's a
   feature. See section 6.7.5, "Commands which operate differently".

7.5. GNU sed v2.05

   (1) If a number follows the substitute command (e.g., s/f/F/10) and
   the number exceeds the possible matches on the pattern space, the
   command 't label' _always_ jumps to the specified label. 't' should
   jump only if the substitution was successful (or returned "true").

   (2) 'l' (list) command does not convert the following characters to
   hex values, but passes them through unchanged: 0xF7, 0xFB, 0xFC,
   0xFD, 0xFE.

   (3) A range address like "/foo/,14" is supposed to match every line
   from the first occurrence of "foo" until line 14, inclusive, and
   then match only those lines containing "foo" thereafter. In gsed
   v2.05, if "foo" occurs later in the file, every line from there to
   the end of file will be matched (since gsed is looking for line 14
   to occur again!).

   (4) The regexes /\`/ and /\'/ are not interpreted as a backquote
   and apostrophe, as might be expected. Instead, they are used to
   represent the beginning-of-line and end-of-line (respectively), to
   conform with similar regexes in the GNU versions of Emacs and awk.
   As a consequence, there is no clear way to indicate an apostrophe,
   since a bare apostrophe (') has special meaning to the Unix shell
   and the quoted apostrophe (\') is interpreted as the EOL. A
   double-quote apostrophe (\\') was interpreted as a backslash to sed
   and a quote mark to the shell--again, not providing the expected
   results. This syntax changed in the next version of gsed.

   (5) Multiple occurrences of the 'w' command fail, as shown here,
   given that both "aaa" and "bbb" occur within the file:

       gsed -e "/aaa/w FILE" -e "/bbb/w FILE" input.txt

   (6) The expression "\<" causes problems when attempting the
   following type of substitution, which should print "+aaa +bbb":

       echo aaa bbb | sed 's/\</+/g'    # sed hangs up with no output

   The syntax 's/\<./+&/g' issues the proper output.

7.6. GNU sed v1.18

   (1) Same as #1 for GNU sed v2.05, above.

   (2) The following command will lock the computer under Win95. Echos
   is an echo command that does not issue a trailing newline:

       echos any_word | gsed "s/[ ]*$//"

   (3) Same as #3 for GNU sed v2.05, above.

7.7. GNU sed v1.03 (by Frank Whaley)

   (1) The \w and \W escape sequences both match only nonword
   characters. \w is misdefined and should match word characters.

   (2) The underscore is defined as a nonword character; it should be
   defined as a word character.

   (3) same as #3 for GNU sed v2.05, above.

7.8. sed v1.6 (by Walter Briscoe) - still in beta version

   (1) Duplicated subexpressions (still) do not match an empty set as
   they should. This problem was inherited from HHsed15.

       echo 123 | sed "s/\([a-z][a-z]\)*/=\1/"  # does not return '='

   (2) If grouping is followed by a + operator, nothing is matched.
   This problem was inherited from HHsed; it fixed a bug with the *
   operator, but the problem with the + operator persists.

       echo aaa | sed "/\(a\)+/d"          # nothing is deleted.

   (3) With the interval expressions \{1,\} and +, there is a bug
   related to the & replacement character. This affected the BETA
   release, and it's not known if it affects the final release.

       echo ab | sed "s/a[^a]*/&c/"        # returns 'abc'. Okay.
       echo ab | sed "s/a[^a]+/&c/"        # returns 'ab'. Bug!
       echo ab | sed "s/a[^a]\{1,\}/&c/"   # returns 'ab'. Bug!

7.9. HHsed v1.5 (by Howard Helman)

   (1) If a number follows the substitute command (e.g., s/foo/bar/2),
   in a sed script entered from the command line, two semicolons must
   follow the number, or they must be separated by an -e switch.
   Normally, only 1 semicolon is needed to separate commands.

       echo bit bet | HHsed "s/b/n/2;;s/b/B/"          # solution 1
       echo bit bet | HHsed -e "s/b/n/2" -e "s/b/B"    # solution 2

   (2) If the substitute command is followed by a number and a "p"
   flag, when the -n switch is used, the "p" flag must occur first.

       echo aaa | HHsed -n "s/./B/3p"    # bug! nothing prints
       echo aaa | HHsed -n "s/./B/p3"    # prints "aaB" as expected

   (3) The following commands will cause HHsed to lock the computer
   under MS-DOS or Win95. Note that they occur because of malformed
   regular expressions which will match no characters.

       sed -n "p;s/\<//g;" file
       sed -n "p;s/[char-set]*//g;" file

   (4) The range command '/RE1/,/RE2/' in HHsed will match one line if
   both regexes occur on the same line (see section 3.4(3), above).
   Though this could be construed as a feature, it should probably be
   considered a bug since its operation differs from every other
   version of sed. For example, '/----/,/----/{s/^/>>/;}' should put
   two angle brackets ">>" before every line which is sandwiched
   between a row of 4 or more hyphens. With HHsed, this command will
   only prefix the hyphens themselves with the angle brackets.

   (5) If the hold space is empty, the H command copies the pattern
   space to the hold space but fails to prepend a leading newline. The
   H command is supposed to add a newline, followed by the contents of
   the pattern space, to the hold space at all times. A workaround is
   "{G;s/^\(.*\)\(\n\)$/\2\1/;H;s/\n$//;}", but it requires knowing
   that the hold space is empty and using the command only once.
   Another alternative is to use the G or the h command alone at key
   points in the script.

   (6) If grouping is followed by an '*' or '+' operator, HHsed does
   not match the pattern, but issues no warning. See below:

       echo aaa | HHsed "/\(a\)*/d"      # nothing is deleted
       echo aaa | HHsed "/\(a\)+/d"      # nothing is deleted
       echo aaa | HHsed "s/\(a\)*/\1B/"  # nothing is changed
       echo aaa | HHsed "s/\(a\)+/\1B/"  # nothing is changed

   (7) If grouping is followed by an interval expression, HHsed halts
   with the error message "garbled command", in all of the following
   examples:

       echo aaa | HHsed "/\(a\)\{3\}/d"
       echo aaa | HHsed "/\(a\)\{1,5\}/d"
       echo aaa | HHsed "s/\(a\)\{3\}/\1B/"

   (8) In interval expressions, 0 is not supported. E.g., \{0,3\)

7.10. sedmod v1.0 (by Hern Chen)

   Technically, the following are limits (or features?) of sedmod, not
   bugs, since the docs for sedmod do not claim to support these
   missing features.

   (1) sedmod does not support standard interval expressions  \{...\}
   present in nearly all versions of sed.

   (2) If grouping is followed by an '*' or '+' operator, sedmod gives
   a "garbled command" message. However, if the grouped expressions
   are strings literals with no metacharacters, a partial workaround
   can be done like so:

       \(string\)\1*    # matches 1 or more instances of 'string'
       \(string\)\1+    # matches 2 or more instances of 'string'

   (3) sedmod does not support a numeric argument after the s///
   command, as in 's/a/b/3', present in nearly all versions of sed.

   The following are bugs in sedmod v1.0:

   (4) When the -i (ignore case) switch is used, the '/regex/d'
   command is not properly obeyed. Sedmod may miss one or more lines
   matching the expression, regardless of where they occur in the
   script. Workaround: use "/regex/{d;}" instead.

7.11. HP-UX sed

   (1) Versions of HP-UX sed up to and including version 10.20 are
   buggy. According to the README file, which comes with the GNU cc
   at <ftp://ftp.ntua.gr/pub/gnu/sed/sed-2.05.bin.README>:

   "When building gcc on a hppa*-*-hpux10 platform, the `fixincludes'
   step (which involves running a sed script) fails because of a bug
   in the vendor's implementation of sed.  Currently the only known
   workaround is to install GNU sed before building gcc.  The file
   sed-2.05.bin.hpux10 is a precompiled binary for that platform."

7.12. SunOS sed v4.1

   (1) Bug occurs in RE pattern matching when a non-null '[char-set]*'
   is followed by a null '\NUM' pattern recall, illustrated here and
   reported by Greg Ubben:

       s/\(a\)\(b*\)cd\1[0-9]*\2foo/bar/  # between '[0-9]*' and '\2'
       s/\(a\{0,1\}\).\{0,1\}\1/bar/      # between '.\{0,1\}' and '\1'

   Workaround: add a do-nothing 'X*' expression which will not match
   any characters on the line between the two components. E.g.,

       s/\(a\)\(b*\)cd\1[0-9]*X*\2foo/bar/
       s/\(a\{0,1\}\).\{0,1\}X*\1/bar/

7.13. SunOS sed v5.6

   (1) If grouping is followed by an asterisk, SunOS sed does not match
   the null string, which it should do. The following command:

       echo foo | sed 's/f\(NO-MATCH\)*/g\1/'

   should transform "foo" to "goo" under normal versions of sed.

7.14. Ultrix sed v4.3

   (1) If grouping is followed by an asterisk, Ultrix sed replies with
   "command garbled", as shown in the following example:

       echo foo | sed 's/f\(NO-MATCH\)*/g\1/'

   (2) If grouping is followed by a numeric operator such as \{0,9\},
   Ultrix sed does not find the match.

7.15. Digital Unix sed

   (1) The following comes from the man pages for sed distributed with
   new, 1998 versions of Digital Unix (reformatted to fit our
   margins):

   [Digital]  The h subcommand for sed does not work properly.  When
   you use the  h subcommand to place text into the hold area, only
   the last line of the specified text is saved.  You can use the H
   subcommand to append text to the hold area. The H subcommand and
   all others dealing with the hold area work correctly.

   (2) "$d" command issues an error message, "cannot parse".  Reported
   by Carlos Duarte on 8 June 1998.

[end-of-file]