     [file version.texi not included]

This file documents GREP, a pattern matching engine.

Published by the Free Software Foundation, 59 Temple Place - Suite 330 Boston, MA 02111-1307, USA

Copyright (C) 1998 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

This document was produced for version VERSION of GNU GREP.

Introduction
************

GREP searches the input files for lines containing a match to a given pattern list.  When it finds a match in a line, it copies the line to standard output (by default), or does whatever other sort of output you have requested with options.  GREP expects to do the matching on text. Since newline is also a separator for the list of patterns, there is no way to match newline characters in a text.

Invoking GREP
*************

GREP comes with a rich set of options from POSIX.2 and GNU extensions.

-c
--count
     Suppress normal output; instead print a count of matching lines for each input file.  With the -v, --revert-match option, count non-matching lines.

-e PATTERN
--regexp=PATTERN
     Use PATTERN as the pattern; useful to protect  patterns beginning with a -.

-f FILE
--file=FILE
     Obtain patterns from FILE, one  per  line.   The  empty file contains zero patterns, and therefore matches nothing.

-i
--ignore-case
     Ignore case distinctions in both the  pattern  and  the input files.

-l
--files-with-matches
     Suppress normal output; instead print the name of  each input file  from which output would normally have been printed. The scanning of every file will stop on the first match.

-n
--line-number
     Prefix each line of output with the line number  within its input file.

-q
--quiet
--silent
     Quiet; suppress normal output.  The scanning of every file will  stop on the first match.  Also see the -s or --no-messages option.

-s
--no-messages
     Suppress error messages about nonexistent or unreadable files. Portability  note:  unlike  GNU GREP, BSD GREP does not comply with POSIX.2, because BSD GREP lacks a -q  option and its -s option behaves like GNU GREP's -q option.  Shell scripts intended to be portable to BSD GREP should avoid both -q and -s and should redirect output to /dev/null instead.

-v
--revert-match
     Invert the sense of matching,  to  select  non-matching lines.

-x
--line-regexp
     Select only those matches that exactly match the  whole line.

GNU Extensions
==============

-A NUM
--after-context=NUM
     Print NUM lines of trailing context after matching lines.

-B NUM
--before-context=NUM
     Print NUM lines of leading context before matching lines.

-C
--context[=NUM]
     Print NUM lines (default 2) of output context.

-NUM
     Same as --context=NUM lines  of  leading  and  trailing context.  However, grep will never print any given line more than once.

-V
--version
     Print the version number of GREP to the standard output stream. This  version  number  should  be  included  in all bug reports.

--help
     Print a usage message briefly summarizing these command-line options and the bug-reporting address, then exit.

-b
--byte-offset
     Print the byte offset within the input file before each line of output. When GREP runs on MS-DOS or MS-Windows, the printed byte offsets depend on whether the -u (--unix-byte-offsets) option is used; see below.

-d ACTION
--directories=ACTION
     If an input file is a directory, use ACTION to  process it. By  default, ACTION is read, which means that directories are read just  as  if  they  were  ordinary files (some operating systems and filesystems disallow this, and will cause GREP to print error messages for every directory).  If ACTION is skip, directories are silently skipped.  If ACTION is recurse, GREP reads all files under each directory, recursively; this is equivalent to the -r option.

-h
--no-filename
     Suppress the prefixing of filenames on output when multiple files are searched.

-L
--files-without-match
     Suppress normal output; instead print the name of  each input file  from  which  no output would normally have been printed. The  scanning of every file will  stop  on  the  first match.

-a
--text
     Do not suppress output lines that contain binary  data. Normally,  if  the  first  few bytes of a file indicate that the file contains binary data, grep outputs only a message saying that the file matches the pattern.  This option causes grep to act as if  the  file  is  a  text file, even if it would otherwise be treated as binary. Warning:  the  result  might  be  binary garbage printed  to  the  terminal,  which  can  have  nasty side-effects if the terminal driver interprets some of it as commands.

-w
--word-regexp
     Select only those lines containing  matches  that  form whole  words.   The test is that the matching substring must either be at the beginning of the  line,  or  preceded by a non-word constituent character.  Similarly, it must be either at the end of the line or followed by a  non-word  constituent  character.   Word-constituent characters are letters, digits, and the underscore.

-r
--recursive
     For each directory mentioned in the command line, read and process all files in that directory, recursively.  This is the same as the -d recurse option.

-y
     Obsolete synonym for -i.

-U
--binary
     Treat the file(s) as binary.  By default, under  MS-DOS and  MS-Windows, GREP guesses the file type by looking at the contents of the first 32KB read from  the  file. If GREP decides the file is a text file, it strips the CR characters from the original file contents (to  make regular  expressions  with  ^ and $ work correctly). Specifying -U overrules this guesswork, causing all files  to  be read and passed to the matching mechanism verbatim; if the file is a text file with  CR/LF  pairs at  the  end of each line, this will cause some regular expressions to fail.  This option is only supported  on MS-DOS and MS-Windows.

-u
--unix-byte-offsets
     Report Unix-style byte  offsets.   This  switch  causes GREP to report byte offsets as if the file were Unix style text file, i.e. the byte offsets ignore the CR characters which were stripped  off.  This  will produce results identical to running GREP on a Unix machine.  This option has no  effect  unless  -b option is also used; it is only supported on MS-DOS and MS-Windows.

Several additional options control which variant of the GREP matching engine is used.  See Grep Programs.

GREP uses the environment variable LANG to provide internationalization support, if compiled with this feature.

Diagnostics
***********

Normally, exit status is 0 if matches were found, and 1 if no matches were found (the -v option inverts the sense of the exit status). Exit status is 2  if  there  were  syntax errors  in  the  pattern, inaccessible input files, or other system errors.

GREP programs
*************

GREP searches the named input files (or standard input if no files are named, or the file name - is given) for lines containing a match to the given pattern.  By default, GREP prints the matching lines. There are three major variants of GREP, controlled by the following options.

-G
--basic-regexp
     Interpret pattern as a basic  regular  expression.  This is the default.

-E

--extended-regexp
     Interpret pattern as  an  extended  regular  expression.

-F
--fixed-strings
     Interpret pattern as a list of fixed strings, separated by newlines, any of which is to be matched.

In addition, two variant programs EGREP and FGREP are available. EGREP is similar (but not identical) to grep -E, and is compatible with the historical Unix EGREP.  FGREP is  the same as grep -F.

Regular Expressions
*******************

A regular expression is a pattern that describes  a  set  of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators  to  combine smaller expressions. GREP understands two different versions of  regular  expression syntax:   ``basic''  and  ``extended''.  In GNU GREP, there is no difference  in  available  functionality  using either  syntax. In  other  implementations,  basic regular expressions are less powerful. The  following  description applies  to  extended  regular  expressions; differences for basic regular expressions are summarized afterwards.

The fundamental building blocks are the regular  expressions that  match a single character.  Most characters, including all letters and digits, are regular expressions  that  match themselves.  Any  metacharacter with special meaning may be quoted by preceding it with a backslash. A list of characters enclosed by [ and ] matches any single character in that list; if the first character of the list is the caret ^, then it matches any character not in the list.  For example, the regular expression [0123456789] matches any single digit. A range of ASCII characters  may be  specified  by  giving  the  first and  last characters, separated by a hyphen.  Finally, certain  named classes  of characters  are  predefined.   Their names are self explanatory, and  they  are :

[:alnum:]
     Any of [:digit:] or [:alpha:]

[:alpha:]
     Any local-specific or one of the ASCII letters:

     a b c d e f g h i j k l m n o p q r s t u v w x y z,

     A B C D E F G H I J K L M N O P Q R S T U V W X Y Z.

[:cntrl:]
     Any of BEL, BS, CR, FF, HT, NL, or VT.

[:digit:]
     Any one of 0 1 2 3 4 5 6 7 8 9.

[:graph:]
     Anything that is not a [:alphanum:] or [:punct:].

[:lower:]
     Any one of a b c d e f g h i j k l m n o p q r s t u v w x y z.

[:print:]
     Any character from the [:space:] class, and any character that is not in the [:isgraph:] class.

[:punct:]
     Any one of ! " #% & ' ( ) ; < = > ? [ \ ] * + , - . / : ^ _ { | }.

[:space:]
     Any one of CR FF HT NL VT SPACE.

[:upper:]
     Any one of A B C D E F G H I J K L M N O P Q R S T U V W X Y Z.

[:xdigit:]
     Any one of a b c d e f A B C D E F 0 1 2 3 4 5 6 7 8 9.

For example, [[:alnum:]] means [0-9A-Za-z], except the latter form is dependent upon the ASCII character  encoding,  whereas  the former  is portable.  (Note that the brackets in these class names are part of the symbolic names, and must  be  included in  addition  to the brackets delimiting the bracket list).  Most metacharacters lose their special meaning inside lists.  To include a literal ], place it first in the list.  Similarly, to include a literal ^, place it anywhere but  first.  Finally, to include a literal -, place it last.

The period . matches any single character.  The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line.  The symbols \< and  \> respectively match the empty string at the beginning and end of a word.  The symbol \b matches the empty string at the edge of a  word,  and  \B matches  the empty string provided it's not at the edge of a word.

A regular expression may  be  followed  by  one  of  several repetition operators:

?
     The preceding item is optional and will be matched at most once.

*
     The preceding item will be matched zero or more times.

+
     The preceding item will be matched one or more times.

{N}
     The preceding item is matched exactly N times.

{N,}
     The preceding item is matched n or more times.

{,M}
     The preceding item is optional and is matched at most M times.

{N,M}
     The preceding item is matched at least N times, but not more than M times.

Two regular expressions may be concatenated;  the  resulting regular expression matches any string formed by concatenating two substrings that respectively match the  concatenated subexpressions.

Two regular expressions may be joined by the infix  operator |; the resulting  regular  expression  matches  any string matching either subexpression.

Repetition takes precedence  over  concatenation,  which  in turn takes precedence over alternation.  A whole subexpression may be enclosed in parentheses to override  these  precedence rules.

The backreference \N, where N is a single digit, matches the substring previously matched by the Nth parenthesized subexpression of the regular expression.

In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

In EGREP the metacharacter  {  loses  its  special  meaning; instead use \{.  This not true for grep -E.

Reporting bugs
**************

Email bug reports to bug-gnu-utils@gnu.org. Be sure to include the word ``grep'' somewhere in the ``Subject:'' field.

Large repetition counts in the  {m,n}  construct  may  cause GREP  to  use  lots  of  memory.  In addition, certain other obscure regular expressions  require  exponential  time  and space, and may cause grep to run out of memory. Backreferences are very slow, and  may  require  exponential time.

Concept Index
*************

This is a general index of all issues discussed in this manual, with the exception of the GREP commands and command-line options.

Index
*****

This is an alphabetical list of all GREP commands and command-line options.