This is grep.info, produced by makeinfo version 4.2 from grep.texi.

START-INFO-DIR-ENTRY
* grep: (grep).                   print lines matching a pattern.
END-INFO-DIR-ENTRY
   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) 2000, 2001 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, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "GNU Free
Documentation License", with no Front-Cover Texts, and with no
Back-Cover Texts.  A copy of the license is included in the section
entitled "GNU Free Documentation License" (*note Copying::).


File: grep.info,  Node: Top,  Next: Introduction,  Up: (dir)

Grep
****

   `grep' searches for lines matching a pattern.

   This document was produced for version 2.5.1 of GNU `grep'.

* Menu:

* Introduction::                Introduction.
* Invoking::                    Invoking `grep'; description of options.
* Diagnostics::                 Exit status returned by `grep'.
* Grep Programs::               `grep' programs.
* Regular Expressions::         Regular Expressions.
* Usage::                       Examples.
* Reporting Bugs::              Reporting Bugs.
* Copying::                     License terms.
* Concept Index::               A menu with all the topics in this manual.
* Index::                       A menu with all `grep' commands
                                 and command-line options.


File: grep.info,  Node: Introduction,  Next: Invoking,  Prev: Top,  Up: Top

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.

   Though `grep' expects to do the matching on text, it has no limits
on input line length other than available memory, and it can match
arbitrary characters within a line.  If the final byte of an input file
is not a newline, `grep' silently supplies one.  Since newline is also
a separator for the list of patterns, there is no way to match newline
characters in a text.


File: grep.info,  Node: Invoking,  Next: Diagnostics,  Prev: Introduction,  Up: Top

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', `--invert-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.

`-o'
`--only-matching'
     Print only the part of matching lines that actually matches
     PATTERN.

`-q'
`--quiet'
`--silent'
     Quiet; do not write anything to standard output.  Exit immediately
     with zero status if any match is found, even if an error was
     detected.  Also see the `-s' or `--no-messages' option.

`-s'
`--no-messages'
     Suppress error messages about nonexistent or unreadable files.
     Portability note: unlike GNU `grep', traditional `grep' did not
     conform to POSIX.2, because traditional `grep' lacked a `-q'
     option and its `-s' option behaved like GNU `grep''s `-q' option.
     Shell scripts intended to be portable to traditional `grep' should
     avoid both `-q' and `-s' and should redirect output to `/dev/null'
     instead.

`-v'
`--invert-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 NUM'
`--context=NUM'
     Print NUM lines of output context.

`--colour[=WHEN]'
`--color[=WHEN]'
     The matching string is surrounded by the marker specify in
     GREP_COLOR.  WHEN may be `never', `always', or `auto'.

`-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.

`--binary-files=TYPE'
     If the first few bytes of a file indicate that the file contains
     binary data, assume that the file is of type TYPE.  By default,
     TYPE is `binary', and `grep' normally outputs either a one-line
     message saying that a binary file matches, or no message if there
     is no match.  If TYPE is `without-match', `grep' assumes that a
     binary file does not match; this is equivalent to the `-I' option.
     If TYPE is `text', `grep' processes a binary file as if it were
     text; this is equivalent to the `-a' option.  _Warning:_
     `--binary-files=text' might output binary garbage, which can have
     nasty side effects if the output is a terminal and if the terminal
     driver interprets some of it as commands.

`-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'
`--devices=ACTION'
     If an input file is a device, FIFO or socket, use ACTION to
     process it.  By default, ACTION is `read', which means that
     devices are read just as if they were ordinary files.  If ACTION
     is `skip', devices, FIFOs and sockets are silently skipped.

`-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 or silently skip them). 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'
`--with-filename'
     Print the filename for each match.

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

`--line-buffered'
     Set the line buffering policy, this can be a performance penality.

`--label=LABEL'
     Displays input actually coming from standard input as input coming
     from file LABEL. This is especially useful for tools like zgrep,
     e.g.  `gzip -cd foo.gz |grep --label=foo something'

`-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'
     Process a binary file as if it were text; this is equivalent to the
     `--binary-files=text' option.

`-I'
     Process a binary file as if it did not contain matching data; this
     is equivalent to the `--binary-files=without-match' option.

`-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'
`-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
     `--directories=recurse' option.

`--include=FILE_PATTERN'
     When processing directories recursively, only files matching
     FILE_PATTERN will be search.

`--exclude=FILE_PATTERN'
     When processing directories recursively, skip files matching
     FILE_PATTERN.

`-m NUM'
`--max-count=NUM'
     Stop reading a file after NUM matching lines.  If the input is
     standard input from a regular file, and NUM matching lines are
     output, `grep' ensures that the standard input is positioned to
     just after the last matching line before exiting, regardless of the
     presence of trailing context lines.  This enables a calling process
     to resume a search.  For example, the following shell script makes
     use of it:

          while grep -m 1 PATTERN
          do
            echo xxxx
          done < FILE

     But the following probably will not work because a pipe is not a
     regular file:

          # This probably will not work.
          cat FILE |
          while grep -m 1 PATTERN
          do
            echo xxxx
          done

     When `grep' stops after NUM matching lines, it outputs any
     trailing context lines. Since context does not include matching
     lines, `grep' will stop when it encounters another matching line.
     When the `-c' or `--count' option is also used, `grep' does not
     output a count greater than NUM.  When the `-v' or
     `--invert-match' option is also used, `grep' stops after
     outputting NUM non-matching lines.

`-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 has no effect on platforms other than 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.  This will produce results identical to running `grep' on
     a Unix machine.  This option has no effect unless `-b' option is
     also used; it has no effect on platforms other than MS-DOS and
     MS-Windows.

`--mmap'
     If possible, use the `mmap' system call to read input, instead of
     the default `read' system call.  In some situations, `--mmap'
     yields better performance.  However, `--mmap' can cause undefined
     behavior (including core dumps) if an input file shrinks while
     `grep' is operating, or if an I/O error occurs.

`-Z'
`--null'
     Output a zero byte (the ASCII `NUL' character) instead of the
     character that normally follows a file name.  For example, `grep
     -lZ' outputs a zero byte after each file name instead of the usual
     newline.  This option makes the output unambiguous, even in the
     presence of file names containing unusual characters like
     newlines.  This option can be used with commands like `find
     -print0', `perl -0', `sort -z', and `xargs -0' to process
     arbitrary file names, even those that contain newline characters.

`-z'
`--null-data'
     Treat the input as a set of lines, each terminated by a zero byte
     (the ASCII `NUL' character) instead of a newline.  Like the `-Z'
     or `--null' option, this option can be used with commands like
     `sort -z' to process arbitrary file names.

   Several additional options control which variant of the `grep'
matching engine is used.  *Note Grep Programs::.

Environment Variables
=====================

   Grep's behavior is affected by the following environment variables.

   A locale `LC_FOO' is specified by examining the three environment
variables `LC_ALL', `LC_FOO', and `LANG', in that order.  The first of
these variables that is set specifies the locale.  For example, if
`LC_ALL' is not set, but `LC_MESSAGES' is set to `pt_BR', then
Brazilian Portuguese is used for the `LC_MESSAGES' locale.  The C
locale is used if none of these environment variables are set, or if
the locale catalog is not installed, or if `grep' was not compiled with
national language support (NLS).

`GREP_OPTIONS'
     This variable specifies default options to be placed in front of
     any explicit options.  For example, if `GREP_OPTIONS' is
     `--binary-files=without-match --directories=skip', `grep' behaves
     as if the two options `--binary-files=without-match' and
     `--directories=skip' had been specified before any explicit
     options.  Option specifications are separated by whitespace.  A
     backslash escapes the next character, so it can be used to specify
     an option containing whitespace or a backslash.

`GREP_COLOR'
     This variable specifies the surrounding markers use to highlight
     the matching text.  The default is control ascii red.

`LC_ALL'
`LC_COLLATE'
`LANG'
     These variables specify the `LC_COLLATE' locale, which determines
     the collating sequence used to interpret range expressions like
     `[a-z]'.

`LC_ALL'
`LC_CTYPE'
`LANG'
     These variables specify the `LC_CTYPE' locale, which determines the
     type of characters, e.g., which characters are whitespace.

`LC_ALL'
`LC_MESSAGES'
`LANG'
     These variables specify the `LC_MESSAGES' locale, which determines
     the language that `grep' uses for messages.  The default C locale
     uses American English messages.

`POSIXLY_CORRECT'
     If set, `grep' behaves as POSIX.2 requires; otherwise, `grep'
     behaves more like other GNU programs.  POSIX.2 requires that
     options that follow file names must be treated as file names; by
     default, such options are permuted to the front of the operand
     list and are treated as options.  Also, POSIX.2 requires that
     unrecognized options be diagnosed as "illegal", but since they are
     not really against the law the default is to diagnose them as
     "invalid".  `POSIXLY_CORRECT' also disables
     `_N_GNU_nonoption_argv_flags_', described below.

`_N_GNU_nonoption_argv_flags_'
     (Here `N' is `grep''s numeric process ID.)  If the Ith character
     of this environment variable's value is `1', do not consider the
     Ith operand of `grep' to be an option, even if it appears to be
     one.  A shell can put this variable in the environment for each
     command it runs, specifying which operands are the results of file
     name wildcard expansion and therefore should not be treated as
     options.  This behavior is available only with the GNU C library,
     and only when `POSIXLY_CORRECT' is not set.


File: grep.info,  Node: Diagnostics,  Next: Grep Programs,  Prev: Invoking,  Up: Top

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

   Normally, exit status is 0 if selected lines are found and 1
otherwise.  But the exit status is 2 if an error occurred, unless the
`-q' or `--quiet' or `--silent' option is used and a selected line is
found.


File: grep.info,  Node: Grep Programs,  Next: Regular Expressions,  Prev: Diagnostics,  Up: Top

`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 four major variants of `grep', controlled by the following
options.

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

`-E'
`--extended-regexp'
     Interpret the pattern as an extended regular expression.

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

`-P'
`--perl-regexp'
     Interpret the pattern as a Perl regular expression.

   In addition, two variant programs EGREP and FGREP are available.
EGREP is the same as `grep -E'.  FGREP is the same as `grep -F'.


File: grep.info,  Node: Regular Expressions,  Next: Usage,  Prev: Grep Programs,  Up: Top

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"(BRE) and "extended"(ERE).  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 regular expression may be followed by one of several repetition
operators:

`.'
     The period `.' matches any single character.

`?'
     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.

`{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.

Character Class
===============

   A "bracket expression" is a list of characters enclosed by `[' and
`]'.  It 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.

   Within a bracket expression, a "range expression" consists of two
characters separated by a hyphen.  It matches any single character that
sorts between the two characters, inclusive, using the locale's
collating sequence and character set.  For example, in the default C
locale, `[a-d]' is equivalent to `[abcd]'.  Many locales sort
characters in dictionary order, and in these locales `[a-d]' is
typically not equivalent to `[abcd]'; it might be equivalent to
`[aBbCcDd]', for example.  To obtain the traditional interpretation of
bracket expressions, you can use the C locale by setting the `LC_ALL'
environment variable to the value `C'.

   Finally, certain named classes of characters are predefined within
bracket expressions, as follows.  Their interpretation depends on the
`LC_CTYPE' locale; the interpretation below is that of the C locale,
which is the default if no `LC_CTYPE' locale is specified.

`[:alnum:]'
     Alphanumeric characters: `[:alpha:]' and `[:digit:]'.

`[:alpha:]'
     Alphabetic characters: `[:lower:]' and `[:upper:]'.

`[:blank:]'
     Blank characters: space and tab.

`[:cntrl:]'
     Control characters.  In ASCII, these characters have octal codes
     000 through 037, and 177 (`DEL').  In other character sets, these
     are the equivalent characters, if any.

`[:digit:]'
     Digits: `0 1 2 3 4 5 6 7 8 9'.

`[:graph:]'
     Graphical characters: `[:alnum:]' and `[:punct:]'.

`[:lower:]'
     Lower-case 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'.

`[:print:]'
     Printable characters: `[:alnum:]', `[:punct:]', and space.

`[:punct:]'
     Punctuation characters: `! " # $ % & ' ( ) * + , - . / : ; < = > ?
     @ [ \ ] ^ _ ` { | } ~'.

`[:space:]'
     Space characters: tab, newline, vertical tab, form feed, carriage
     return, and space.

`[:upper:]'
     Upper-case 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'.

`[:xdigit:]'
     Hexadecimal digits: `0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f'.

   For example, `[[:alnum:]]' means `[0-9A-Za-z]', except the latter
depends upon the C locale and the ASCII character encoding, whereas the
former is independent of locale and character set.  (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.

`]'
     ends the list if it's not the first list item.  So, if you want to
     make the `]' character a list item, you must put it first.

`[.'
     represents the open collating symbol.

`.]'
     represents the close collating symbol.

`[='
     represents the open equivalence class.

`=]'
     represents the close equivalence class.

`[:'
     represents the open character class followed by a valid character
     class name.

`:]'
     represents the close character class followed by a valid character
     class name.

`-'
     represents the range if it's not first or last in a list or the
     ending point of a range.

`^'
     represents the characters not in the list.  If you want to make
     the `^' character a list item, place it anywhere but first.

Backslash Character
===================

   The `\' when followed by certain ordinary characters take a special
meaning :

``\b''
     Match the empty string at the edge of a word.

``\B''
     Match the empty string provided it's not at the edge of a word.

``\<''
     Match the empty string at the beginning of word.

``\>''
     Match the empty string at the end of word.

``\w''
     Match word constituent, it is a synonym for `[[:alnum:]]'.

``\W''
     Match non word constituent, it is a synonym for `[^[:alnum:]]'.

   For example , `\brat\b' matches the separate word `rat', `c\Brat\Be'
matches `crate', but `dirty \Brat' doesn't match `dirty rat'.

Anchoring
=========

   The caret `^' and the dollar sign `$' are metacharacters that
respectively match the empty string at the beginning and end of a line.

Back-reference
==============

   The back-reference `\N', where N is a single digit, matches the
substring previously matched by the Nth parenthesized subexpression of
the regular expression. For example, `(a)\1' matches `aa'.  When use
with alternation if the group does not participate in the match, then
the back-reference makes the whole match fail.  For example, `a(.)|b\1'
will not match `ba'.  When multiple regular expressions are given with
`-e' or from a file `-f file', the back-referecences are local to each
expression.

Basic vs Extended
=================

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

   Traditional `egrep' did not support the `{' metacharacter, and some
`egrep' implementations support `\{' instead, so portable scripts
should avoid `{' in `egrep' patterns and should use `[{]' to match a
literal `{'.

   GNU `egrep' attempts to support traditional usage by assuming that
`{' is not special if it would be the start of an invalid interval
specification.  For example, the shell command `egrep '{1'' searches
for the two-character string `{1' instead of reporting a syntax error
in the regular expression.  POSIX.2 allows this behavior as an
extension, but portable scripts should avoid it.


File: grep.info,  Node: Usage,  Next: Reporting Bugs,  Prev: Regular Expressions,  Up: Top

Usage
*****

   Here is an example shell command that invokes GNU `grep':

     grep -i 'hello.*world' menu.h main.c

This lists all lines in the files `menu.h' and `main.c' that contain
the string `hello' followed by the string `world'; this is because `.*'
matches zero or more characters within a line.  *Note Regular
Expressions::.  The `-i' option causes `grep' to ignore case, causing
it to match the line `Hello, world!', which it would not otherwise
match.  *Note Invoking::, for more details about how to invoke `grep'.

   Here are some common questions and answers about `grep' usage.

  1. How can I list just the names of matching files?

          grep -l 'main' *.c

     lists the names of all C files in the current directory whose
     contents mention `main'.

  2. How do I search directories recursively?

          grep -r 'hello' /home/gigi

     searches for `hello' in all files under the directory
     `/home/gigi'.  For more control of which files are searched, use
     `find', `grep' and `xargs'.  For example, the following command
     searches only C files:

          find /home/gigi -name '*.c' -print | xargs grep 'hello' /dev/null

     This differs from the command:

          grep -r 'hello' *.c

     which merely looks for `hello' in all files in the current
     directory whose names end in `.c'.  Here the `-r' is probably
     unnecessary, as recursion occurs only in the unlikely event that
     one of `.c' files is a directory.

  3. What if a pattern has a leading `-'?

          grep -e '--cut here--' *

     searches for all lines matching `--cut here--'.  Without `-e',
     `grep' would attempt to parse `--cut here--' as a list of options.

  4. Suppose I want to search for a whole word, not a part of a word?

          grep -w 'hello' *

     searches only for instances of `hello' that are entire words; it
     does not match `Othello'.  For more control, use `\<' and `\>' to
     match the start and end of words.  For example:

          grep 'hello\>' *

     searches only for words ending in `hello', so it matches the word
     `Othello'.

  5. How do I output context around the matching lines?

          grep -C 2 'hello' *

     prints two lines of context around each matching line.

  6. How do I force grep to print the name of the file?

     Append `/dev/null':

          grep 'eli' /etc/passwd /dev/null

     gets you:

          /etc/passwd:eli:DNGUTF58.IMe.:98:11:Eli Smith:/home/do/eli:/bin/bash

  7. Why do people use strange regular expressions on `ps' output?

          ps -ef | grep '[c]ron'

     If the pattern had been written without the square brackets, it
     would have matched not only the `ps' output line for `cron', but
     also the `ps' output line for `grep'.  Note that some platforms
     `ps' limit the ouput to the width of the screen, grep does not
     have any limit on the length of a line except the available memory.

  8. Why does `grep' report "Binary file matches"?

     If `grep' listed all matching "lines" from a binary file, it would
     probably generate output that is not useful, and it might even
     muck up your display.  So GNU `grep' suppresses output from files
     that appear to be binary files.  To force GNU `grep' to output
     lines even from files that appear to be binary, use the `-a' or
     `--binary-files=text' option.  To eliminate the "Binary file
     matches" messages, use the `-I' or `--binary-files=without-match'
     option.

  9. Why doesn't `grep -lv' print nonmatching file names?

     `grep -lv' lists the names of all files containing one or more
     lines that do not match.  To list the names of all files that
     contain no matching lines, use the `-L' or `--files-without-match'
     option.

 10. I can do OR with `|', but what about AND?

          grep 'paul' /etc/motd | grep 'franc,ois'

     finds all lines that contain both `paul' and `franc,ois'.

 11. How can I search in both standard input and in files?

     Use the special file name `-':

          cat /etc/passwd | grep 'alain' - /etc/motd

 12. How to express palindromes in a regular expression?

     It can be done by using the back referecences, for example a
     palindrome of 4 chararcters can be written in BRE.

          grep -w -e '\(.\)\(.\).\2\1' file

     It matches the word "radar" or "civic".

     Guglielmo Bondioni proposed a single RE that finds all the
     palindromes up to 19 characters long.

          egrep -e '^(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?).?\9\8\7\6\5\4\3\2\1$' file

     Note this is done by using GNU ERE extensions, it might not be
     portable on other greps.

 13. Why are my expressions whith the vertical bar fail?

          /bin/echo "ba" | egrep '(a)\1|(b)\1'

     The first alternate branch fails then the first group was not in
     the match this will make the second alternate branch fails.  For
     example, "aaba" will match, the first group participate in the
     match and can be reuse in the second branch.

 14. What do `grep, fgrep, egrep' stand for ?

     grep comes from the way line editing was done on Unix.  For
     example, `ed' uses this syntax to print a list of matching lines
     on the screen.

          global/regular expression/print
          g/re/p

     `fgrep' stands for Fixed `grep', `egrep' Extended `grep'.



File: grep.info,  Node: Reporting Bugs,  Next: Copying,  Prev: Usage,  Up: Top

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 `{n,m}' 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.  Back-references are very slow, and may require
exponential time.


File: grep.info,  Node: Copying,  Next: GNU General Public License,  Prev: Reporting Bugs,  Up: Top

Copying
*******

   GNU grep is licensed under the GNU GPL, which makes it "free
software".

   Please note that "free" in "free software" refers to liberty, not
price.  As some GNU project advocates like to point out, think of "free
speech" rather than "free beer".  The exact and legally binding
distribution terms are spelled out below; in short, you have the right
(freedom) to run and change grep and distribute it to other people, and
even--if you want--charge money for doing either.  The important
restriction is that you have to grant your recipients the same rights
and impose the same restrictions.

   This method of licensing software is also known as "open source"
because, among other things, it makes sure that all recipients will
receive the source code along with the program, and be able to improve
it.  The GNU project prefers the term "free software" for reasons
outlined at
<http://www.gnu.org/philosophy/free-software-for-freedom.html>.

   The exact license terms are defined by this paragraph and the GNU
General Public License it refers to:

     GNU grep is free software; you can redistribute it and/or modify it
     under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     GNU grep is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     A copy of the GNU General Public License is included as part of
     this manual; if you did not receive it, write to the Free Software
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   In addition to this, this manual is free in the same sense:

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with the Invariant Sections being "GNU General Public
     License" and "GNU Free Documentation License", with no Front-Cover
     Texts, and with no Back-Cover Texts.  A copy of the license is
     included in the section entitled "GNU Free Documentation License".

   The full texts of the GNU General Public License and of the GNU Free
Documentation License are available below.

* Menu:

* GNU General Public License:: GNU GPL
* GNU Free Documentation License:: GNU FDL

