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, write us and we'll try to clarify it for the
   next version of the FAQ.

1.2. Latest version of the sed FAQ
   The newest version of the sed FAQ is usually here:

      http://www.cornerstonemag.com/sed/sedfaq.html
      http://www.cornerstonemag.com/sed/sedfaq.txt
      http://www.dbnet.ece.ntua.gr/~george/sed/sedfaq.html
      http://www.dbnet.ece.ntua.gr/~george/sed/sedfaq.txt
      http://www.ptug.org/sed/sedfaq.html
      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
   Changes to this FAQ since the last version are indicated 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 succinctly and clearly, and e-mail it Eric
   Pement <epement@jpusa.org>, indicating your proposed addition to
   the FAQ. We'll post it on the sed-users mailing list (see section
   2.3.2, below) and discuss it there. If some agreement, your
   contribution will be included in the next edition of the FAQ.

1.5. FAQ abbreviations:
   files = one or more filenames, separated by whitespace
   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.

   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 the syntax of Basic Regular Expressions (BREs), type "man
   ed" and read the documentation for regular expressions. A technical
   description of BREs from the Single UNIX Specification, Version 2,
   by The Open Group (joint committee on Unix) is available online at
   <http://www.opengroup.org/onlinepubs/7908799/xbd/re.html#tag_007_003>.
   Sed normally supports BREs plus '\n' to match a newline in the
   pattern space and '\xREx' as equivalent to '/RE/', where 'x' is any
   character other than 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 6.8.3 ("Special syntax in REs"), below.

   LHS: In sed, the LHS may be a string literal (e.g., "foo") or any
   valid regular expression supported by your version of sed. Some
   versions of sed support things like \t for TAB, \r for carriage
   return, \xNN for direct entry of hex codes, etc. Other versions of
   sed do not support this syntax.

   RHS: The right-hand side (the replacement part in s/find/replace/)
   is almost always a string literal, with no interpolation of the
   metacharacters (.), (^), ($), ([), or \(...\) -- with the following
   exceptions:  \1 through \9 are replaced by the corresponding group,
   if grouping \(...\) was used in the LHS.  If no grouping was used
   in the LHS, then \1 through \9 are replaced by literal digits. '&'
   is replaced by the entire expression matched on the LHS. To enter a
   literal ampersand or backslash in the RHS, type '\&' or '\\'.

1.6. Credits and acknowledgements
   My time spent messing with sed, composing this FAQ, and generally
   doing text manipulation which is unrelated to my job description is
   due to the kind tolerance of the Christian magazine I work for,
   Cornerstone. So, let me say thanks to the mag staff for indulging
   this somewhat unusual "ministry." Please visit this site:

      http://www.cornerstonemag.com

   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 Perl FAQ
      http://www.perl.com/perl/FAQ
      http://www.perl.com/CPAN/doc/FAQs/FAQ/html/index.html
      ftp://ftp.cdrom.com/pub/perl/CPAN/doc/FAQs/

   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 <af137@freenet*toronto*on*ca>
      Yiorgos Adamopoulos <adamo@softlab*ece*ntua*gr>

      Walter Briscoe <walter@wbriscoe*demon*co*uk>
      Jim Dennis <jadestar@rahul*net>
      Carlos Duarte <cdua@algos*inesc*pt>
      Otavio Exel <oexel@economatica*com*br>
      Mark Katz <mark@ispc001*demon*co*uk>

      Eric Pement <epement@jpusa*org>
      Greg Pfeiffer <gpfeiffe@yahoo*com>
      Ken Pizzini <ken@halcyon*com>
      Niall Smart <nialls@euristix*ie>
      Simon Taylor <staylor@unisolve*com*au>

      Greg Ubben <gsu@romulus*ncsc*mil>

   Note: Periods (.) are replaced with asterisks (*) to foil e-mail
   harvesting and spam-bots.

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 errors or
   ambiguous wording, please notify the FAQ maintainer so it can be
   fixed for the next edition.