grep.txt

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

grep
****

‘grep’ prints lines that contain a match for one or more patterns.

   This manual is for version 3.4 of GNU Grep.

   This manual is for ‘grep’, a pattern matching engine.

   Copyright © 1999–2002, 2005, 2008–2020 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included in
     the section entitled “GNU Free Documentation License”.

* Menu:

* Introduction::                Introduction.
* Invoking::                    Command-line options, environment, exit status.
* Regular Expressions::         Regular Expressions.
* Usage::                       Examples.
* Performance::                 Performance tuning.
* Reporting Bugs::              Reporting Bugs.
* Copying::                     License terms for this manual.
* Index::                       Combined index.

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

1 Introduction
**************

Given one or more patterns, ‘grep’ searches input files for matches to
the patterns.  When it finds a match in a line, it copies the line to
standard output (by default), or produces 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: Regular Expressions,  Prev: Introduction,  Up: Top

2 Invoking ‘grep’
*****************

The general synopsis of the ‘grep’ command line is

     grep [OPTION...] [PATTERNS] [FILE...]

There can be zero or more OPTION arguments, and zero or more FILE
arguments.  The PATTERNS argument contains one or more patterns
separated by newlines, and is omitted when patterns are given via the
‘-e PATTERNS’ or ‘-f FILE’ options.  Typically PATTERNS should be quoted
when ‘grep’ is used in a shell command.

* Menu:

* Command-line Options::        Short and long names, grouped by category.
* Environment Variables::       POSIX, GNU generic, and GNU grep specific.
* Exit Status::                 Exit status returned by ‘grep’.
* grep Programs::               ‘grep’ programs.

File: grep.info,  Node: Command-line Options,  Next: Environment Variables,  Up: Invoking

2.1 Command-line Options
========================

‘grep’ comes with a rich set of options: some from POSIX and some being
GNU extensions.  Long option names are always a GNU extension, even for
options that are from POSIX specifications.  Options that are specified
by POSIX, under their short names, are explicitly marked as such to
facilitate POSIX-portable programming.  A few option names are provided
for compatibility with older or more exotic implementations.

* Menu:

* Generic Program Information::
* Matching Control::
* General Output Control::
* Output Line Prefix Control::
* Context Line Control::
* File and Directory Selection::
* Other Options::

   Several additional options control which variant of the ‘grep’
matching engine is used.  *Note grep Programs::.

File: grep.info,  Node: Generic Program Information,  Next: Matching Control,  Up: Command-line Options

2.1.1 Generic Program Information
---------------------------------

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

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

File: grep.info,  Node: Matching Control,  Next: General Output Control,  Prev: Generic Program Information,  Up: Command-line Options

2.1.2 Matching Control
----------------------

‘-e PATTERNS’
‘--regexp=PATTERNS’
     Use PATTERNS as one or more patterns; newlines within PATTERNS
     separate each pattern from the next.  If this option is used
     multiple times or is combined with the ‘-f’ (‘--file’) option,
     search for all patterns given.  Typically PATTERNS should be quoted
     when ‘grep’ is used in a shell command.  (‘-e’ is specified by
     POSIX.)

‘-f FILE’
‘--file=FILE’
     Obtain patterns from FILE, one per line.  If this option is used
     multiple times or is combined with the ‘-e’ (‘--regexp’) option,
     search for all patterns given.  The empty file contains zero
     patterns, and therefore matches nothing.  (‘-f’ is specified by
     POSIX.)

‘-i’
‘-y’
‘--ignore-case’
     Ignore case distinctions in patterns and input data, so that
     characters that differ only in case match each other.  Although
     this is straightforward when letters differ in case only via
     lowercase-uppercase pairs, the behavior is unspecified in other
     situations.  For example, uppercase “S” has an unusual lowercase
     counterpart “ſ” (Unicode character U+017F, LATIN SMALL LETTER LONG
     S) in many locales, and it is unspecified whether this unusual
     character matches “S” or “s” even though uppercasing it yields “S”.
     Another example: the lowercase German letter “ß” (U+00DF, LATIN
     SMALL LETTER SHARP S) is normally capitalized as the two-character
     string “SS” but it does not match “SS”, and it might not match the
     uppercase letter “ẞ” (U+1E9E, LATIN CAPITAL LETTER SHARP S) even
     though lowercasing the latter yields the former.

     ‘-y’ is an obsolete synonym that is provided for compatibility.
     (‘-i’ is specified by POSIX.)

‘--no-ignore-case’
     Do not ignore case distinctions in patterns and input data.  This
     is the default.  This option is useful for passing to shell scripts
     that already use ‘-i’, in order to cancel its effects because the
     two options override each other.

‘-v’
‘--invert-match’
     Invert the sense of matching, to select non-matching lines.  (‘-v’
     is specified by POSIX.)

‘-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.  This option
     has no effect if ‘-x’ is also specified.

     Because the ‘-w’ option can match a substring that does not begin
     and end with word constituents, it differs from surrounding a
     regular expression with ‘\<’ and ‘\>’.  For example, although ‘grep
     -w @’ matches a line containing only ‘@’, ‘grep '\<@\>'’ cannot
     match any line because ‘@’ is not a word constituent.  *Note The
     Backslash Character and Special Expressions::.

‘-x’
‘--line-regexp’
     Select only those matches that exactly match the whole line.  For
     regular expression patterns, this is like parenthesizing each
     pattern and then surrounding it with ‘^’ and ‘$’.  (‘-x’ is
     specified by POSIX.)

File: grep.info,  Node: General Output Control,  Next: Output Line Prefix Control,  Prev: Matching Control,  Up: Command-line Options

2.1.3 General Output Control
----------------------------

‘-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.  (‘-c’ is specified by POSIX.)

‘--color[=WHEN]’
‘--colour[=WHEN]’
     Surround the matched (non-empty) strings, matching lines, context
     lines, file names, line numbers, byte offsets, and separators (for
     fields and groups of context lines) with escape sequences to
     display them in color on the terminal.  The colors are defined by
     the environment variable ‘GREP_COLORS’ and default to
     ‘ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36’ for bold red
     matched text, magenta file names, green line numbers, green byte
     offsets, cyan separators, and default terminal colors otherwise.
     The deprecated environment variable ‘GREP_COLOR’ is still
     supported, but its setting does not have priority; it defaults to
     ‘01;31’ (bold red) which only covers the color for matched text.
     WHEN is ‘never’, ‘always’, or ‘auto’.

‘-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 each file stops on the first match.

‘-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 each file stops on the first match.  (‘-l’ is specified by
     POSIX.)

‘-m NUM’
‘--max-count=NUM’
     Stop after the first NUM selected lines.  If the input is standard
     input from a regular file, and NUM selected lines are output,
     ‘grep’ ensures that the standard input is positioned just after the
     last selected 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 selected lines, it outputs any trailing
     context lines.  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.

‘-o’
‘--only-matching’
     Print only the matched (non-empty) parts of matching lines, with
     each such part on a separate output line.  Output lines use the
     same delimiters as input, and delimiters are null bytes if ‘-z’
     (‘--null-data’) is also used (*note Other Options::).

‘-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.  (‘-q’ is
     specified by POSIX.)

‘-s’
‘--no-messages’
     Suppress error messages about nonexistent or unreadable files.
     Portability note: unlike GNU ‘grep’, 7th Edition Unix ‘grep’ did
     not conform to POSIX, because it lacked ‘-q’ and its ‘-s’ option
     behaved like GNU ‘grep’’s ‘-q’ option.(1)  USG-style ‘grep’ also
     lacked ‘-q’ but its ‘-s’ option behaved like GNU ‘grep’’s.
     Portable shell scripts should avoid both ‘-q’ and ‘-s’ and should
     redirect standard and error output to ‘/dev/null’ instead.  (‘-s’
     is specified by POSIX.)

   ---------- Footnotes ----------

   (1) Of course, 7th Edition Unix predated POSIX by several years!

File: grep.info,  Node: Output Line Prefix Control,  Next: Context Line Control,  Prev: General Output Control,  Up: Command-line Options

2.1.4 Output Line Prefix Control
--------------------------------

When several prefix fields are to be output, the order is always file
name, line number, and byte offset, regardless of the order in which
these options were specified.

‘-b’
‘--byte-offset’
     Print the 0-based byte offset within the input file before each
     line of output.  If ‘-o’ (‘--only-matching’) is specified, print
     the offset of the matching part itself.

‘-H’
‘--with-filename’
     Print the file name for each match.  This is the default when there
     is more than one file to search.

‘-h’
‘--no-filename’
     Suppress the prefixing of file names on output.  This is the
     default when there is only one file (or only standard input) to
     search.

‘--label=LABEL’
     Display input actually coming from standard input as input coming
     from file LABEL.  This can be useful for commands that transform a
     file’s contents before searching; e.g.:

          gzip -cd foo.gz | grep --label=foo -H 'some pattern'

‘-n’
‘--line-number’
     Prefix each line of output with the 1-based line number within its
     input file.  (‘-n’ is specified by POSIX.)

‘-T’
‘--initial-tab’
     Make sure that the first character of actual line content lies on a
     tab stop, so that the alignment of tabs looks normal.  This is
     useful with options that prefix their output to the actual content:
     ‘-H’, ‘-n’, and ‘-b’.  This may also prepend spaces to output line
     numbers and byte offsets so that lines from a single file all start
     at the same column.

‘-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.

File: grep.info,  Node: Context Line Control,  Next: File and Directory Selection,  Prev: Output Line Prefix Control,  Up: Command-line Options

2.1.5 Context Line Control
--------------------------

“Context lines” are non-matching lines that are near a matching line.
They are output only if one of the following options are used.
Regardless of how these options are set, ‘grep’ never outputs any given
line more than once.  If the ‘-o’ (‘--only-matching’) option is
specified, these options have no effect and a warning is given upon
their use.

‘-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’
‘-NUM’
‘--context=NUM’
     Print NUM lines of leading and trailing output context.

‘--group-separator=STRING’
     When ‘-A’, ‘-B’ or ‘-C’ are in use, print STRING instead of ‘--’
     between groups of lines.

‘--no-group-separator’
     When ‘-A’, ‘-B’ or ‘-C’ are in use, do not print a separator
     between groups of lines.

   Here are some points about how ‘grep’ chooses the separator to print
between prefix fields and line content:

   • Matching lines normally use ‘:’ as a separator between prefix
     fields and actual line content.

   • Context (i.e., non-matching) lines use ‘-’ instead.

   • When context is not specified, matching lines are simply output one
     right after another.

   • When context is specified, lines that are adjacent in the input
     form a group and are output one right after another, while by
     default a separator appears between non-adjacent groups.

   • The default separator is a ‘--’ line; its presence and appearance
     can be changed with the options above.

   • Each group may contain several matching lines when they are close
     enough to each other that two adjacent groups connect and can merge
     into a single contiguous one.

File: grep.info,  Node: File and Directory Selection,  Next: Other Options,  Prev: Context Line Control,  Up: Command-line Options

2.1.6 File and Directory Selection
----------------------------------

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

‘--binary-files=TYPE’
     If a file’s data or metadata indicate that the file contains binary
     data, assume that the file is of type TYPE.  Non-text bytes
     indicate binary data; these are either output bytes that are
     improperly encoded for the current locale (*note Environment
     Variables::), or null input bytes when the ‘-z’ (‘--null-data’)
     option is not given (*note Other Options::).

     By default, TYPE is ‘binary’, and ‘grep’ suppresses output after
     null input binary data is discovered, and suppresses output lines
     that contain improperly encoded data.  When some output is
     suppressed, ‘grep’ follows any output with a one-line message
     saying that a binary file matches.

     If TYPE is ‘without-match’, when ‘grep’ discovers null input binary
     data it assumes that the rest of the file does not match; this is
     equivalent to the ‘-I’ option.

     If TYPE is ‘text’, ‘grep’ processes binary data as if it were text;
     this is equivalent to the ‘-a’ option.

     When TYPE is ‘binary’, ‘grep’ may treat non-text bytes as line
     terminators even without the ‘-z’ (‘--null-data’) option.  This
     means choosing ‘binary’ versus ‘text’ can affect whether a pattern
     matches a file.  For example, when TYPE is ‘binary’ the pattern
     ‘q$’ might match ‘q’ immediately followed by a null byte, even
     though this is not matched when TYPE is ‘text’.  Conversely, when
     TYPE is ‘binary’ the pattern ‘.’ (period) might not match a null
     byte.

     _Warning:_ The ‘-a’ (‘--binary-files=text’) option 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.  On the other hand, when reading files whose text
     encodings are unknown, it can be helpful to use ‘-a’ or to set
     ‘LC_ALL='C'’ in the environment, in order to find more matches even
     if the matches are unsafe for direct display.

‘-D ACTION’
‘--devices=ACTION’
     If an input file is a device, FIFO, or socket, use ACTION to
     process it.  If ACTION is ‘read’, all devices are read just as if
     they were ordinary files.  If ACTION is ‘skip’, devices, FIFOs, and
     sockets are silently skipped.  By default, devices are read if they
     are on the command line or if the ‘-R’ (‘--dereference-recursive’)
     option is used, and are skipped if they are encountered recursively
     and the ‘-r’ (‘--recursive’) option is used.  This option has no
     effect on a file that is read via standard input.

‘-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
     file systems 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, following
     command-line symbolic links and skipping other symlinks; this is
     equivalent to the ‘-r’ option.

‘--exclude=GLOB’
     Skip any command-line file with a name suffix that matches the
     pattern GLOB, using wildcard matching; a name suffix is either the
     whole name, or a trailing part that starts with a non-slash
     character immediately after a slash (‘/’) in the name.  When
     searching recursively, skip any subfile whose base name matches
     GLOB; the base name is the part after the last slash.  A pattern
     can use ‘*’, ‘?’, and ‘[’...‘]’  as wildcards, and ‘\’ to quote a
     wildcard or backslash character literally.

‘--exclude-from=FILE’
     Skip files whose name matches any of the patterns read from FILE
     (using wildcard matching as described under ‘--exclude’).

‘--exclude-dir=GLOB’
     Skip any command-line directory with a name suffix that matches the
     pattern GLOB.  When searching recursively, skip any subdirectory
     whose base name matches GLOB.  Ignore any redundant trailing
     slashes in GLOB.

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

‘--include=GLOB’
     Search only files whose name matches GLOB, using wildcard matching
     as described under ‘--exclude’.

‘-r’
‘--recursive’
     For each directory operand, read and process all files in that
     directory, recursively.  Follow symbolic links on the command line,
     but skip symlinks that are encountered recursively.  Note that if
     no file operand is given, grep searches the working directory.
     This is the same as the ‘--directories=recurse’ option.

‘-R’
‘--dereference-recursive’
     For each directory operand, read and process all files in that
     directory, recursively, following all symbolic links.

File: grep.info,  Node: Other Options,  Prev: File and Directory Selection,  Up: Command-line Options

2.1.7 Other Options
-------------------

‘--’
     Delimit the option list.  Later arguments, if any, are treated as
     operands even if they begin with ‘-’.  For example, ‘grep PAT --
     -file1 file2’ searches for the pattern PAT in the files named
     ‘-file1’ and ‘file2’.

‘--line-buffered’
     Use line buffering on output.  This can cause a performance
     penalty.

‘-U’
‘--binary’
     On platforms that distinguish between text and binary I/O, use the
     latter when reading and writing files other than the user’s
     terminal, so that all input bytes are read and written as-is.  This
     overrides the default behavior where ‘grep’ follows the operating
     system’s advice whether to use text or binary I/O.  On MS-Windows
     when ‘grep’ uses text I/O it reads a carriage return–newline pair
     as a newline and a Control-Z as end-of-file, and it writes a
     newline as a carriage return–newline pair.

     When using text I/O ‘--byte-offset’ (‘-b’) counts and
     ‘--binary-files’ heuristics apply to input data after text-I/O
     processing.  Also, the ‘--binary-files’ heuristics need not agree
     with the ‘--binary’ option; that is, they may treat the data as
     text even if ‘--binary’ is given, or vice versa.  *Note File and
     Directory Selection::.

     This option has no effect on GNU and other POSIX-compatible
     platforms, which do not distinguish text from binary I/O.

‘-z’
‘--null-data’
     Treat input and output data as sequences 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.

File: grep.info,  Node: Environment Variables,  Next: Exit Status,  Prev: Command-line Options,  Up: Invoking

2.2 Environment Variables
=========================

The behavior of ‘grep’ is affected by the following environment
variables.

   The locale for category ‘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_COLLATE’ is set to ‘pt_BR’,
then the Brazilian Portuguese locale is used for the ‘LC_COLLATE’
category.  As a special case for ‘LC_MESSAGES’ only, the environment
variable ‘LANGUAGE’ can contain a colon-separated list of languages that
overrides the three environment variables that ordinarily specify the
‘LC_MESSAGES’ category.  The ‘C’ locale is used if none of these
environment variables are set, if the locale catalog is not installed,
or if ‘grep’ was not compiled with national language support (NLS). The
shell command ‘locale -a’ lists locales that are currently available.

   Many of the environment variables in the following list let you
control highlighting using Select Graphic Rendition (SGR) commands
interpreted by the terminal or terminal emulator.  (See the section in
the documentation of your text terminal for permitted values and their
meanings as character attributes.)  These substring values are integers
in decimal representation and can be concatenated with semicolons.
‘grep’ takes care of assembling the result into a complete SGR sequence
(‘\33[’...‘m’).  Common values to concatenate include ‘1’ for bold, ‘4’
for underline, ‘5’ for blink, ‘7’ for inverse, ‘39’ for default
foreground color, ‘30’ to ‘37’ for foreground colors, ‘90’ to ‘97’ for
16-color mode foreground colors, ‘38;5;0’ to ‘38;5;255’ for 88-color and
256-color modes foreground colors, ‘49’ for default background color,
‘40’ to ‘47’ for background colors, ‘100’ to ‘107’ for 16-color mode
background colors, and ‘48;5;0’ to ‘48;5;255’ for 88-color and 256-color
modes background colors.

   The two-letter names used in the ‘GREP_COLORS’ environment variable
(and some of the others) refer to terminal “capabilities,” the ability
of a terminal to highlight text, or change its color, and so on.  These
capabilities are stored in an online database and accessed by the
‘terminfo’ library.

‘GREP_OPTIONS’
     This variable specifies default options to be placed in front of
     any explicit options.  As this causes problems when writing
     portable scripts, this feature will be removed in a future release
     of ‘grep’, and ‘grep’ warns if it is used.  Please use an alias or
     script instead.  For example, if ‘grep’ is in the directory
     ‘/usr/bin’ you can prepend ‘$HOME/bin’ to your ‘PATH’ and create an
     executable script ‘$HOME/bin/grep’ containing the following:

          #! /bin/sh
          export PATH=/usr/bin
          exec grep --color=auto --devices=skip "$@"

‘GREP_COLOR’
     This variable specifies the color used to highlight matched
     (non-empty) text.  It is deprecated in favor of ‘GREP_COLORS’, but
     still supported.  The ‘mt’, ‘ms’, and ‘mc’ capabilities of
     ‘GREP_COLORS’ have priority over it.  It can only specify the color
     used to highlight the matching non-empty text in any matching line
     (a selected line when the ‘-v’ command-line option is omitted, or a
     context line when ‘-v’ is specified).  The default is ‘01;31’,
     which means a bold red foreground text on the terminal’s default
     background.

‘GREP_COLORS’
     This variable specifies the colors and other attributes used to
     highlight various parts of the output.  Its value is a
     colon-separated list of ‘terminfo’ capabilities that defaults to
     ‘ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36’ with the ‘rv’
     and ‘ne’ boolean capabilities omitted (i.e., false).  Supported
     capabilities are as follows.

     ‘sl=’
          SGR substring for whole selected lines (i.e., matching lines
          when the ‘-v’ command-line option is omitted, or non-matching
          lines when ‘-v’ is specified).  If however the boolean ‘rv’
          capability and the ‘-v’ command-line option are both
          specified, it applies to context matching lines instead.  The
          default is empty (i.e., the terminal’s default color pair).

     ‘cx=’
          SGR substring for whole context lines (i.e., non-matching
          lines when the ‘-v’ command-line option is omitted, or
          matching lines when ‘-v’ is specified).  If however the
          boolean ‘rv’ capability and the ‘-v’ command-line option are
          both specified, it applies to selected non-matching lines
          instead.  The default is empty (i.e., the terminal’s default
          color pair).

     ‘rv’
          Boolean value that reverses (swaps) the meanings of the ‘sl=’
          and ‘cx=’ capabilities when the ‘-v’ command-line option is
          specified.  The default is false (i.e., the capability is
          omitted).

     ‘mt=01;31’
          SGR substring for matching non-empty text in any matching line
          (i.e., a selected line when the ‘-v’ command-line option is
          omitted, or a context line when ‘-v’ is specified).  Setting
          this is equivalent to setting both ‘ms=’ and ‘mc=’ at once to
          the same value.  The default is a bold red text foreground
          over the current line background.

     ‘ms=01;31’
          SGR substring for matching non-empty text in a selected line.
          (This is used only when the ‘-v’ command-line option is
          omitted.)  The effect of the ‘sl=’ (or ‘cx=’ if ‘rv’)
          capability remains active when this takes effect.  The default
          is a bold red text foreground over the current line
          background.

     ‘mc=01;31’
          SGR substring for matching non-empty text in a context line.
          (This is used only when the ‘-v’ command-line option is
          specified.)  The effect of the ‘cx=’ (or ‘sl=’ if ‘rv’)
          capability remains active when this takes effect.  The default
          is a bold red text foreground over the current line
          background.

     ‘fn=35’
          SGR substring for file names prefixing any content line.  The
          default is a magenta text foreground over the terminal’s
          default background.

     ‘ln=32’
          SGR substring for line numbers prefixing any content line.
          The default is a green text foreground over the terminal’s
          default background.

     ‘bn=32’
          SGR substring for byte offsets prefixing any content line.
          The default is a green text foreground over the terminal’s
          default background.

     ‘se=36’
          SGR substring for separators that are inserted between
          selected line fields (‘:’), between context line fields (‘-’),
          and between groups of adjacent lines when nonzero context is
          specified (‘--’).  The default is a cyan text foreground over
          the terminal’s default background.

     ‘ne’
          Boolean value that prevents clearing to the end of line using
          Erase in Line (EL) to Right (‘\33[K’) each time a colorized
          item ends.  This is needed on terminals on which EL is not
          supported.  It is otherwise useful on terminals for which the
          ‘back_color_erase’ (‘bce’) boolean ‘terminfo’ capability does
          not apply, when the chosen highlight colors do not affect the
          background, or when EL is too slow or causes too much flicker.
          The default is false (i.e., the capability is omitted).

     Note that boolean capabilities have no ‘=’...  part.  They are
     omitted (i.e., false) by default and become true when specified.

‘LC_ALL’
‘LC_COLLATE’
‘LANG’
     These variables specify the locale for the ‘LC_COLLATE’ category,
     which might affect how range expressions like ‘[a-z]’ are
     interpreted.

‘LC_ALL’
‘LC_CTYPE’
‘LANG’
     These variables specify the locale for the ‘LC_CTYPE’ category,
     which determines the type of characters, e.g., which characters are
     whitespace.  This category also determines the character encoding,
     that is, whether text is encoded in UTF-8, ASCII, or some other
     encoding.  In the ‘C’ or ‘POSIX’ locale, all characters are encoded
     as a single byte and every byte is a valid character.  In
     more-complex encodings such as UTF-8, a sequence of multiple bytes
     may be needed to represent a character, and some bytes may be
     encoding errors that do not contribute to the representation of any
     character.  POSIX does not specify the behavior of ‘grep’ when
     patterns or input data contain encoding errors or null characters,
     so portable scripts should avoid such usage.  As an extension to
     POSIX, GNU ‘grep’ treats null characters like any other character.
     However, unless the ‘-a’ (‘--binary-files=text’) option is used,
     the presence of null characters in input or of encoding errors in
     output causes GNU ‘grep’ to treat the file as binary and suppress
     details about matches.  *Note File and Directory Selection::.

‘LANGUAGE’
‘LC_ALL’
‘LC_MESSAGES’
‘LANG’
     These variables specify the locale for the ‘LC_MESSAGES’ category,
     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 requires; otherwise, ‘grep’ behaves
     more like other GNU programs.  POSIX 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, ‘POSIXLY_CORRECT’ disables special
     handling of an invalid bracket expression.  *Note
     invalid-bracket-expr::.

‘_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: Exit Status,  Next: grep Programs,  Prev: Environment Variables,  Up: Invoking

2.3 Exit Status
===============

Normally the exit status is 0 if a line is selected, 1 if no lines were
selected, and 2 if an error occurred.  However, if the ‘-L’ or
‘--files-without-match’ is used, the exit status is 0 if a file is
listed, 1 if no files were listed, and 2 if an error occurred.  Also, if
the ‘-q’ or ‘--quiet’ or ‘--silent’ option is used and a line is
selected, the exit status is 0 even if an error occurred.  Other ‘grep’
implementations may exit with status greater than 2 on error.

File: grep.info,  Node: grep Programs,  Prev: Exit Status,  Up: Invoking

2.4 ‘grep’ Programs
===================

‘grep’ searches the named input files for lines containing a match to
the given patterns.  By default, ‘grep’ prints the matching lines.  A
file named ‘-’ stands for standard input.  If no input is specified,
‘grep’ searches the working directory ‘.’ if given a command-line option
specifying recursion; otherwise, ‘grep’ searches standard input.  There
are four major variants of ‘grep’, controlled by the following options.

‘-G’
‘--basic-regexp’
     Interpret patterns as basic regular expressions (BREs).  This is
     the default.

‘-E’
‘--extended-regexp’
     Interpret patterns as extended regular expressions (EREs).  (‘-E’
     is specified by POSIX.)

‘-F’
‘--fixed-strings’
     Interpret patterns as fixed strings, not regular expressions.
     (‘-F’ is specified by POSIX.)

‘-P’
‘--perl-regexp’
     Interpret patterns as Perl-compatible regular expressions (PCREs).
     PCRE support is here to stay, but consider this option experimental
     when combined with the ‘-z’ (‘--null-data’) option, and note that
     ‘grep -P’ may warn of unimplemented features.  *Note Other
     Options::.

   In addition, two variant programs ‘egrep’ and ‘fgrep’ are available.
‘egrep’ is the same as ‘grep -E’.  ‘fgrep’ is the same as ‘grep -F’.
Direct invocation as either ‘egrep’ or ‘fgrep’ is deprecated, but is
provided to allow historical applications that rely on them to run
unmodified.

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

3 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 three different versions of regular expression
syntax: basic (BRE), extended (ERE), and Perl-compatible (PCRE). In GNU
‘grep’, there is no difference in available functionality between the
basic and extended syntaxes.  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.  Perl-compatible regular expressions give
additional functionality, and are documented in the pcresyntax(3) and
pcrepattern(3) manual pages, but work only if PCRE is available in the
system.

* Menu:

* Fundamental Structure::
* Character Classes and Bracket Expressions::
* The Backslash Character and Special Expressions::
* Anchoring::
* Back-references and Subexpressions::
* Basic vs Extended::

File: grep.info,  Node: Fundamental Structure,  Next: Character Classes and Bracket Expressions,  Up: Regular Expressions

3.1 Fundamental Structure
=========================

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 meta-character with
special meaning may be quoted by preceding it with a backslash.

   The period ‘.’ matches any single character.  It is unspecified
whether ‘.’ matches an encoding error.

   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 matched at most M times.  This is a GNU
     extension.

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

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

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

   Repetition takes precedence over concatenation, which in turn takes
precedence over alternation.  A whole expression may be enclosed in
parentheses to override these precedence rules and form a subexpression.
An unmatched ‘)’ matches just itself.

File: grep.info,  Node: Character Classes and Bracket Expressions,  Next: The Backslash Character and Special Expressions,  Prev: Fundamental Structure,  Up: Regular Expressions

3.2 Character Classes and Bracket Expressions
=============================================

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, and it is unspecified whether it matches an encoding error.  For
example, the regular expression ‘[0123456789]’ matches any single digit,
whereas ‘[^()]’ matches any single character that is not an opening or
closing parenthesis, and might or might not match an encoding error.

   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.  In the default C locale,
the sorting sequence is the native character order; for example, ‘[a-d]’
is equivalent to ‘[abcd]’.  In other locales, the sorting sequence is
not specified, and ‘[a-d]’ might be equivalent to ‘[abcd]’ or to
‘[aBbCcDd]’, or it might fail to match any character, or the set of
characters that it matches might even be erratic.  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; for example, ‘[[:alnum:]]’ means the character class
of numbers and letters in the current locale.

‘[:alnum:]’
     Alphanumeric characters: ‘[:alpha:]’ and ‘[:digit:]’; in the ‘C’
     locale and ASCII character encoding, this is the same as
     ‘[0-9A-Za-z]’.

‘[:alpha:]’
     Alphabetic characters: ‘[:lower:]’ and ‘[:upper:]’; in the ‘C’
     locale and ASCII character encoding, this is the same as
     ‘[A-Za-z]’.

‘[: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; in the ‘C’ locale and ASCII character encoding,
     this is ‘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; in the ‘C’ locale and ASCII character
     encoding, this is ‘! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \
     ] ^ _ ` { | } ~’.

‘[:space:]’
     Space characters: in the ‘C’ locale, this is tab, newline, vertical
     tab, form feed, carriage return, and space.  *Note Usage::, for
     more discussion of matching newlines.

‘[:upper:]’
     Upper-case letters: in the ‘C’ locale and ASCII character encoding,
     this is ‘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’.

   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 expression.

   If you mistakenly omit the outer brackets, and search for say,
‘[:upper:]’, GNU ‘grep’ prints a diagnostic and exits with status 2, on
the assumption that you did not intend to search for the nominally
equivalent regular expression: ‘[:epru]’.  Set the ‘POSIXLY_CORRECT’
environment variable to disable this feature.

   Most meta-characters lose their special meaning inside bracket
expressions.

‘]’
     ends the bracket expression 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 symbol, and should be followed
     by a valid character class name.

‘:]’
     represents the close character class symbol.

‘-’
     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.

File: grep.info,  Node: The Backslash Character and Special Expressions,  Next: Anchoring,  Prev: Character Classes and Bracket Expressions,  Up: Regular Expressions

3.3 The Backslash Character and Special Expressions
===================================================

The ‘\’ character, when followed by certain ordinary characters, takes 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:]]’.

‘\s’
     Match whitespace, it is a synonym for ‘[[:space:]]’.

‘\S’
     Match non-whitespace, it is a synonym for ‘[^[:space:]]’.

   For example, ‘\brat\b’ matches the separate word ‘rat’, ‘\Brat\B’
matches ‘crate’ but not ‘furry rat’.

File: grep.info,  Node: Anchoring,  Next: Back-references and Subexpressions,  Prev: The Backslash Character and Special Expressions,  Up: Regular Expressions

3.4 Anchoring
=============

The caret ‘^’ and the dollar sign ‘$’ are meta-characters that
respectively match the empty string at the beginning and end of a line.
They are termed “anchors”, since they force the match to be “anchored”
to beginning or end of a line, respectively.

File: grep.info,  Node: Back-references and Subexpressions,  Next: Basic vs Extended,  Prev: Anchoring,  Up: Regular Expressions

3.5 Back-references and Subexpressions
======================================

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 used
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’), back-references are local to each
expression.

   *Note Known Bugs::, for some known problems with back-references.

File: grep.info,  Node: Basic vs Extended,  Prev: Back-references and Subexpressions,  Up: Regular Expressions

3.6 Basic vs Extended Regular Expressions
=========================================

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

   Traditional ‘egrep’ did not support the ‘{’ meta-character, and some
‘egrep’ implementations support ‘\{’ instead, so portable scripts should
avoid ‘{’ in ‘grep -E’ patterns and should use ‘[{]’ to match a literal
‘{’.

   GNU ‘grep -E’ 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 command ‘grep -E '{1'’ searches for the
two-character string ‘{1’ instead of reporting a syntax error in the
regular expression.  POSIX allows this behavior as an extension, but
portable scripts should avoid it.

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

4 Usage
*******

Here is an example 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.

   Here is a more complex example session, showing the location and
contents of any line containing ‘f’ and ending in ‘.c’, within all files
in the current directory whose names contain ‘g’ and end in ‘.h’.  The
‘-n’ option outputs line numbers, the ‘--’ argument treats any later
arguments starting with ‘-’ as file names not options, and the empty
file ‘/dev/null’ causes file names to be output even if only one file
name happens to be of the form ‘*g*.h’.

     $ grep -n -- 'f.*\.c$' *g*.h /dev/null
     argmatch.h:1:/* definitions and prototypes for argmatch.c

The only line that contains a match is line 1 of ‘argmatch.h’.  Note
that the regular expression syntax used in the pattern differs from the
globbing syntax that the shell uses to match file names.

   *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' test-*.c

     lists names of ‘test-*.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 ‘/home/gigi’ directory.
     For more control over which files are searched, use ‘find’ and
     ‘grep’.  For example, the following command searches only C files:

          find /home/gigi -name '*.c' ! -type d \
            -exec grep -H 'hello' '{}' +

     This differs from the command:

          grep -H 'hello' /home/gigi/*.c

     which merely looks for ‘hello’ in non-hidden C files in
     ‘/home/gigi’ whose names end in ‘.c’.  The ‘find’ command line
     above is more similar to the command:

          grep -r --include='*.c' 'hello' /home/gigi

  3. What if a pattern or file has a leading ‘-’?

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

     searches for all lines matching ‘--cut here--’.  Without ‘--’,
     ‘grep’ would attempt to parse ‘--cut here--’ as a list of options,
     and there would be similar problems with any file names beginning
     with ‘-’.

     Alternatively, you can prevent misinterpretation of leading ‘-’ by
     using ‘-e’ for patterns and leading ‘./’ for files:

          grep -e '--cut here--' ./*

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

          grep -w 'hello' test*.log

     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\>' test*.log

     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' test*.log

     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:x:2098:1000:Eli Smith:/home/eli:/bin/bash

     Alternatively, use ‘-H’, which is a GNU extension:

          grep -H 'eli' /etc/passwd

  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 on some platforms,
     ‘ps’ limits the output 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 non-matching 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. Why does the empty pattern match every input line?

     The ‘grep’ command searches for lines that contain strings that
     match a pattern.  Every line contains the empty string, so an empty
     pattern causes ‘grep’ to find a match on each line.  It is not the
     only such pattern: ‘^’, ‘$’, and many other patterns cause ‘grep’
     to match every line.

     To match empty lines, use the pattern ‘^$’.  To match blank lines,
     use the pattern ‘^[[:blank:]]*$’.  To match no lines at all, use
     the command ‘grep -f /dev/null’.

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

     Use the special file name ‘-’:

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

  13. Why is this back-reference failing?

          echo 'ba' | grep -E '(a)\1|b\1'

     This gives no output, because the first alternate ‘(a)\1’ does not
     match, as there is no ‘aa’ in the input, so the ‘\1’ in the second
     alternate has nothing to refer back to, meaning it will never match
     anything.  (The second alternate in this example can only match if
     the first alternate has matched—making the second one superfluous.)

  14. How can I match across lines?

     Standard grep cannot do this, as it is fundamentally line-based.
     Therefore, merely using the ‘[:space:]’ character class does not
     match newlines in the way you might expect.

     With the GNU ‘grep’ option ‘-z’ (‘--null-data’), each input and
     output “line” is null-terminated; *note Other Options::.  Thus, you
     can match newlines in the input, but typically if there is a match
     the entire input is output, so this usage is often combined with
     output-suppressing options like ‘-q’, e.g.:

          printf 'foo\nbar\n' | grep -z -q 'foo[[:space:]]\+bar'

     If this does not suffice, you can transform the input before giving
     it to ‘grep’, or turn to ‘awk’, ‘sed’, ‘perl’, or many other
     utilities that are designed to operate across lines.

  15. What do ‘grep’, ‘fgrep’, and ‘egrep’ stand for?

     The name ‘grep’ comes from the way line editing was done on Unix.
     For example, ‘ed’ uses the following syntax to print a list of
     matching lines on the screen:

          global/regular expression/print
          g/re/p

     ‘fgrep’ stands for Fixed ‘grep’; ‘egrep’ stands for Extended
     ‘grep’.

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

5 Performance
*************

Typically ‘grep’ is an efficient way to search text.  However, it can be
quite slow in some cases, and it can search large files where even minor
performance tweaking can help significantly.  Although the algorithm
used by ‘grep’ is an implementation detail that can change from release
to release, understanding its basic strengths and weaknesses can help
you improve its performance.

   The ‘grep’ command operates partly via a set of automata that are
designed for efficiency, and partly via a slower matcher that takes over
when the fast matchers run into unusual features like back-references.
When feasible, the Boyer–Moore fast string searching algorithm is used
to match a single fixed pattern, and the Aho–Corasick algorithm is used
to match multiple fixed patterns.

   Generally speaking ‘grep’ operates more efficiently in single-byte
locales, since it can avoid the special processing needed for multi-byte
characters.  If your patterns will work just as well that way, setting
‘LC_ALL’ to a single-byte locale can help performance considerably.
Setting ‘LC_ALL='C'’ can be particularly efficient, as ‘grep’ is tuned
for that locale.

   Outside the ‘C’ locale, case-insensitive search, and search for
bracket expressions like ‘[a-z]’ and ‘[[=a=]b]’, can be surprisingly
inefficient due to difficulties in fast portable access to concepts like
multi-character collating elements.

   A back-reference such as ‘\1’ can hurt performance significantly in
some cases, since back-references cannot in general be implemented via a
finite state automaton, and instead trigger a backtracking algorithm
that can be quite inefficient.  For example, although the pattern
‘^(.*)\1{14}(.*)\2{13}$’ matches only lines whose lengths can be written
as a sum 15x + 14y for nonnegative integers x and y, the pattern matcher
does not perform linear Diophantine analysis and instead backtracks
through all possible matching strings, using an algorithm that is
exponential in the worst case.

   On some operating systems that support files with holes—large regions
of zeros that are not physically present on secondary storage—‘grep’ can
skip over the holes efficiently without needing to read the zeros.  This
optimization is not available if the ‘-a’ (‘--binary-files=text’) option
is used (*note File and Directory Selection::), unless the ‘-z’
(‘--null-data’) option is also used (*note Other Options::).

   For more about the algorithms used by ‘grep’ and about related string
matching algorithms, see:

   • Aho AV. Algorithms for finding patterns in strings. In: van Leeuwen
     J. _Handbook of Theoretical Computer Science_, vol. A. New York:
     Elsevier; 1990. p. 255–300. This surveys classic string matching
     algorithms, some of which are used by ‘grep’.

   • Aho AV, Corasick MJ. Efficient string matching: an aid to
     bibliographic search. _CACM_. 1975;18(6):333–40.
     <https://dx.doi.org/10.1145/360825.360855>. This introduces the
     Aho–Corasick algorithm.

   • Boyer RS, Moore JS. A fast string searching algorithm. _CACM_.
     1977;20(10):762–72. <https://dx.doi.org/10.1145/359842.359859>.
     This introduces the Boyer–Moore algorithm.

   • Faro S, Lecroq T. The exact online string matching problem: a
     review of the most recent results. _ACM Comput Surv_.
     2013;45(2):13. <https://dx.doi.org/10.1145/2431211.2431212>. This
     surveys string matching algorithms that might help improve the
     performance of ‘grep’ in the future.

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

6 Reporting bugs
****************

Bug reports can be found at the GNU bug report logs for ‘grep’
(https://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep).  If you find a
bug not listed there, please email it to <bug-grep@gnu.org> to create a
new bug report.

* Menu:

* Known Bugs::

File: grep.info,  Node: Known Bugs,  Up: Reporting Bugs

6.1 Known Bugs
==============

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 can greatly slow down matching, as they can generate
exponentially many matching possibilities that can consume both time and
memory to explore.  Also, the POSIX specification for back-references is
at times unclear.  Furthermore, many regular expression implementations
have back-reference bugs that can cause programs to return incorrect
answers or even crash, and fixing these bugs has often been
low-priority—for example, as of 2019 the GNU C library bug database
contained back-reference bugs 52, 10844, 11053, and 25322, with little
sign of forthcoming fixes.  Luckily, back-references are rarely useful
and it should be little trouble to avoid them in practical applications.

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

7 Copying
*********

GNU ‘grep’ is licensed under the GNU GPL, which makes it “free
software”.

   The “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”.  In short, you have the right (freedom) to run and
change ‘grep’ and distribute it to other people, and—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 general method of licensing software is sometimes called “open
source”.  The GNU project prefers the term “free software” for reasons
outlined at
<https://www.gnu.org/philosophy/open-source-misses-the-point.html>.

   This manual is free documentation in the same sense.  The
documentation license is included below.  The license for the program is
available with the source code, or at
<https://www.gnu.org/licenses/gpl.html>.

* Menu:

* GNU Free Documentation License::

File: grep.info,  Node: GNU Free Documentation License,  Up: Copying

7.1 GNU Free Documentation License
==================================

                     Version 1.3, 3 November 2008

     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     <https://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document “free” in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of “copyleft”, which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.  We
     recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it can
     be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     “Document”, below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as “you”.  You accept
     the license if you copy, modify or distribute the work in a way
     requiring permission under copyright law.

     A “Modified Version” of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A “Secondary Section” is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document’s overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The “Invariant Sections” are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in the
     notice that says that the Document is released under this License.
     If a section does not fit the above definition of Secondary then it
     is not allowed to be designated as Invariant.  The Document may
     contain zero Invariant Sections.  If the Document does not identify
     any Invariant Sections then there are none.

     The “Cover Texts” are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A “Transparent” copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images composed
     of pixels) generic paint programs or (for drawings) some widely
     available drawing editor, and that is suitable for input to text
     formatters or for automatic translation to a variety of formats
     suitable for input to text formatters.  A copy made in an otherwise
     Transparent file format whose markup, or absence of markup, has
     been arranged to thwart or discourage subsequent modification by
     readers is not Transparent.  An image format is not Transparent if
     used for any substantial amount of text.  A copy that is not
     “Transparent” is called “Opaque”.

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and standard-conforming
     simple HTML, PostScript or PDF designed for human modification.
     Examples of transparent image formats include PNG, XCF and JPG.
     Opaque formats include proprietary formats that can be read and
     edited only by proprietary word processors, SGML or XML for which
     the DTD and/or processing tools are not generally available, and
     the machine-generated HTML, PostScript or PDF produced by some word
     processors for output purposes only.

     The “Title Page” means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, “Title
     Page” means the text near the most prominent appearance of the
     work’s title, preceding the beginning of the body of the text.

     The “publisher” means any person or entity that distributes copies
     of the Document to the public.

     A section “Entitled XYZ” means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.)
     To “Preserve the Title” of such a section when you modify the
     Document means that it remains a section “Entitled XYZ” according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow the
     conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document’s license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the title
     equally prominent and visible.  You may add other material on the
     covers in addition.  Copying with changes limited to the covers, as
     long as they preserve the title of the Document and satisfy these
     conditions, can be treated as verbatim copying in other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a machine-readable
     Transparent copy along with each Opaque copy, or state in or with
     each Opaque copy a computer-network location from which the general
     network-using public has access to download using public-standard
     network protocols a complete Transparent copy of the Document, free
     of added material.  If you use the latter option, you must take
     reasonably prudent steps, when you begin distribution of Opaque
     copies in quantity, to ensure that this Transparent copy will
     remain thus accessible at the stated location until at least one
     year after the last time you distribute an Opaque copy (directly or
     through your agents or retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of copies,
     to give them a chance to provide you with an updated version of the
     Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with the
     Modified Version filling the role of the Document, thus licensing
     distribution and modification of the Modified Version to whoever
     possesses a copy of it.  In addition, you must do these things in
     the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of previous
          versions (which should, if there were any, be listed in the
          History section of the Document).  You may use the same title
          as a previous version if the original publisher of that
          version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document’s
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled “History”, Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on the
          Title Page.  If there is no section Entitled “History” in the
          Document, create one stating the title, year, authors, and
          publisher of the Document as given on its Title Page, then add
          an item describing the Modified Version as stated in the
          previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in the
          “History” section.  You may omit a network location for a work
          that was published at least four years before the Document
          itself, or if the original publisher of the version it refers
          to gives permission.

       K. For any section Entitled “Acknowledgements” or “Dedications”,
          Preserve the Title of the section, and preserve in the section
          all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document, unaltered
          in their text and in their titles.  Section numbers or the
          equivalent are not considered part of the section titles.

       M. Delete any section Entitled “Endorsements”.  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          “Endorsements” or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option designate
     some or all of these sections as invariant.  To do this, add their
     titles to the list of Invariant Sections in the Modified Version’s
     license notice.  These titles must be distinct from any other
     section titles.

     You may add a section Entitled “Endorsements”, provided it contains
     nothing but endorsements of your Modified Version by various
     parties—for example, statements of peer review or that the text has
     been approved by an organization as the authoritative definition of
     a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end of
     the list of Cover Texts in the Modified Version.  Only one passage
     of Front-Cover Text and one of Back-Cover Text may be added by (or
     through arrangements made by) any one entity.  If the Document
     already includes a cover text for the same cover, previously added
     by you or by arrangement made by the same entity you are acting on
     behalf of, you may not add another; but you may replace the old
     one, on explicit permission from the previous publisher that added
     the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination all
     of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     “History” in the various original documents, forming one section
     Entitled “History”; likewise combine any sections Entitled
     “Acknowledgements”, and any sections Entitled “Dedications”.  You
     must delete all sections Entitled “Endorsements.”

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the documents
     in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow this
     License in all other respects regarding verbatim copying of that
     document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of a
     storage or distribution medium, is called an “aggregate” if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation’s users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document’s Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled “Acknowledgements”,
     “Dedications”, or “History”, the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense, or distribute it is void,
     and will automatically terminate your rights under this License.

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, receipt of a copy of some or all of the
     same material does not give you any rights to use it.

  10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     <https://www.gnu.org/copyleft/>.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License “or any later version” applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If the
     Document does not specify a version number of this License, you may
     choose any version ever published (not as a draft) by the Free
     Software Foundation.  If the Document specifies that a proxy can
     decide which future versions of this License can be used, that
     proxy’s public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

  11. RELICENSING

     “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any
     World Wide Web server that publishes copyrightable works and also
     provides prominent facilities for anybody to edit those works.  A
     public wiki that anybody can edit is an example of such a server.
     A “Massive Multiauthor Collaboration” (or “MMC”) contained in the
     site means any set of copyrightable works thus published on the MMC
     site.

     “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0
     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
     published by that same organization.

     “Incorporate” means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is “eligible for relicensing” if it is licensed under this
     License, and if all works that were first published under this
     License somewhere other than this MMC, and subsequently
     incorporated in whole or in part into the MMC, (1) had no cover
     texts or invariant sections, and (2) were thus incorporated prior
     to November 1, 2008.

     The operator of an MMC Site may republish an MMC contained in the
     site under CC-BY-SA on the same site at any time before August 1,
     2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.

File: grep.info,  Node: Index,  Prev: Copying,  Up: Top

Index
*****


* Menu:

* *:                                     Fundamental Structure.
                                                              (line  21)
* +:                                     Fundamental Structure.
                                                              (line  24)
* --:                                    Other Options.       (line   7)
* --after-context:                       Context Line Control.
                                                              (line  15)
* --basic-regexp:                        grep Programs.       (line  15)
* --before-context:                      Context Line Control.
                                                              (line  19)
* --binary:                              Other Options.       (line  18)
* --binary-files:                        File and Directory Selection.
                                                              (line  12)
* --byte-offset:                         Output Line Prefix Control.
                                                              (line  12)
* --color:                               General Output Control.
                                                              (line  14)
* --colour:                              General Output Control.
                                                              (line  14)
* --context:                             Context Line Control.
                                                              (line  24)
* --count:                               General Output Control.
                                                              (line   8)
* --dereference-recursive:               File and Directory Selection.
                                                              (line 110)
* --devices:                             File and Directory Selection.
                                                              (line  51)
* --directories:                         File and Directory Selection.
                                                              (line  62)
* --exclude:                             File and Directory Selection.
                                                              (line  73)
* --exclude-dir:                         File and Directory Selection.
                                                              (line  87)
* --exclude-from:                        File and Directory Selection.
                                                              (line  83)
* --extended-regexp:                     grep Programs.       (line  20)
* --file:                                Matching Control.    (line  17)
* --files-with-matches:                  General Output Control.
                                                              (line  35)
* --files-without-match:                 General Output Control.
                                                              (line  29)
* --fixed-strings:                       grep Programs.       (line  25)
* --group-separator:                     Context Line Control.
                                                              (line  27)
* --group-separator <1>:                 Context Line Control.
                                                              (line  31)
* --help:                                Generic Program Information.
                                                              (line   7)
* --ignore-case:                         Matching Control.    (line  26)
* --include:                             File and Directory Selection.
                                                              (line  97)
* --initial-tab:                         Output Line Prefix Control.
                                                              (line  41)
* --invert-match:                        Matching Control.    (line  51)
* --label:                               Output Line Prefix Control.
                                                              (line  28)
* --line-buffered:                       Other Options.       (line  13)
* --line-number:                         Output Line Prefix Control.
                                                              (line  36)
* --line-regexp:                         Matching Control.    (line  73)
* --max-count:                           General Output Control.
                                                              (line  42)
* --no-filename:                         Output Line Prefix Control.
                                                              (line  23)
* --no-ignore-case:                      Matching Control.    (line  44)
* --no-messages:                         General Output Control.
                                                              (line  87)
* --null:                                Output Line Prefix Control.
                                                              (line  50)
* --null-data:                           Other Options.       (line  39)
* --only-matching:                       General Output Control.
                                                              (line  72)
* --perl-regexp:                         grep Programs.       (line  30)
* --quiet:                               General Output Control.
                                                              (line  80)
* --recursive:                           File and Directory Selection.
                                                              (line 102)
* --regexp=PATTERNS:                     Matching Control.    (line   8)
* --silent:                              General Output Control.
                                                              (line  80)
* --text:                                File and Directory Selection.
                                                              (line   8)
* --version:                             Generic Program Information.
                                                              (line  12)
* --with-filename:                       Output Line Prefix Control.
                                                              (line  18)
* --word-regexp:                         Matching Control.    (line  56)
* -A:                                    Context Line Control.
                                                              (line  15)
* -a:                                    File and Directory Selection.
                                                              (line   8)
* -b:                                    Output Line Prefix Control.
                                                              (line  12)
* -B:                                    Context Line Control.
                                                              (line  19)
* -c:                                    General Output Control.
                                                              (line   8)
* -C:                                    Context Line Control.
                                                              (line  24)
* -D:                                    File and Directory Selection.
                                                              (line  51)
* -d:                                    File and Directory Selection.
                                                              (line  62)
* -e:                                    Matching Control.    (line   8)
* -E:                                    grep Programs.       (line  20)
* -f:                                    Matching Control.    (line  17)
* -F:                                    grep Programs.       (line  25)
* -G:                                    grep Programs.       (line  15)
* -H:                                    Output Line Prefix Control.
                                                              (line  18)
* -h:                                    Output Line Prefix Control.
                                                              (line  23)
* -i:                                    Matching Control.    (line  26)
* -L:                                    General Output Control.
                                                              (line  29)
* -l:                                    General Output Control.
                                                              (line  35)
* -m:                                    General Output Control.
                                                              (line  42)
* -n:                                    Output Line Prefix Control.
                                                              (line  36)
* -NUM:                                  Context Line Control.
                                                              (line  24)
* -o:                                    General Output Control.
                                                              (line  72)
* -P:                                    grep Programs.       (line  30)
* -q:                                    General Output Control.
                                                              (line  80)
* -r:                                    File and Directory Selection.
                                                              (line 102)
* -R:                                    File and Directory Selection.
                                                              (line 110)
* -s:                                    General Output Control.
                                                              (line  87)
* -T:                                    Output Line Prefix Control.
                                                              (line  41)
* -U:                                    Other Options.       (line  18)
* -V:                                    Generic Program Information.
                                                              (line  12)
* -v:                                    Matching Control.    (line  51)
* -w:                                    Matching Control.    (line  56)
* -x:                                    Matching Control.    (line  73)
* -y:                                    Matching Control.    (line  26)
* -Z:                                    Output Line Prefix Control.
                                                              (line  50)
* -z:                                    Other Options.       (line  39)
* .:                                     Fundamental Structure.
                                                              (line  11)
* ?:                                     Fundamental Structure.
                                                              (line  18)
* _N_GNU_nonoption_argv_flags_ environment variable: Environment Variables.
                                                              (line 204)
* {,M}:                                  Fundamental Structure.
                                                              (line  33)
* {N,M}:                                 Fundamental Structure.
                                                              (line  37)
* {N,}:                                  Fundamental Structure.
                                                              (line  30)
* {N}:                                   Fundamental Structure.
                                                              (line  27)
* after context:                         Context Line Control.
                                                              (line  15)
* alnum character class:                 Character Classes and Bracket Expressions.
                                                              (line  31)
* alpha character class:                 Character Classes and Bracket Expressions.
                                                              (line  36)
* alphabetic characters:                 Character Classes and Bracket Expressions.
                                                              (line  36)
* alphanumeric characters:               Character Classes and Bracket Expressions.
                                                              (line  31)
* anchoring:                             Anchoring.           (line   6)
* asterisk:                              Fundamental Structure.
                                                              (line  21)
* back-reference:                        Back-references and Subexpressions.
                                                              (line   6)
* back-references:                       Performance.         (line  32)
* backslash:                             The Backslash Character and Special Expressions.
                                                              (line   6)
* basic regular expressions:             Basic vs Extended.   (line   6)
* before context:                        Context Line Control.
                                                              (line  19)
* binary files:                          File and Directory Selection.
                                                              (line   8)
* binary files <1>:                      File and Directory Selection.
                                                              (line  12)
* binary I/O:                            Other Options.       (line  18)
* blank character class:                 Character Classes and Bracket Expressions.
                                                              (line  41)
* blank characters:                      Character Classes and Bracket Expressions.
                                                              (line  41)
* bn GREP_COLORS capability:             Environment Variables.
                                                              (line 134)
* braces, first argument omitted:        Fundamental Structure.
                                                              (line  33)
* braces, one argument:                  Fundamental Structure.
                                                              (line  27)
* braces, second argument omitted:       Fundamental Structure.
                                                              (line  30)
* braces, two arguments:                 Fundamental Structure.
                                                              (line  37)
* bracket expression:                    Character Classes and Bracket Expressions.
                                                              (line   6)
* Bugs, known:                           Known Bugs.          (line   6)
* bugs, reporting:                       Reporting Bugs.      (line   6)
* byte offset:                           Output Line Prefix Control.
                                                              (line  12)
* case insensitive search:               Matching Control.    (line  26)
* case insensitive search <1>:           Performance.         (line  27)
* changing name of standard input:       Output Line Prefix Control.
                                                              (line  28)
* character class:                       Character Classes and Bracket Expressions.
                                                              (line   6)
* character classes:                     Character Classes and Bracket Expressions.
                                                              (line  30)
* character type:                        Environment Variables.
                                                              (line 161)
* classes of characters:                 Character Classes and Bracket Expressions.
                                                              (line  30)
* cntrl character class:                 Character Classes and Bracket Expressions.
                                                              (line  44)
* context lines:                         General Output Control.
                                                              (line  64)
* context lines <1>:                     Context Line Control.
                                                              (line   6)
* context lines <2>:                     Context Line Control.
                                                              (line  24)
* context lines, after match:            Context Line Control.
                                                              (line  15)
* context lines, before match:           Context Line Control.
                                                              (line  19)
* control characters:                    Character Classes and Bracket Expressions.
                                                              (line  44)
* copying:                               Copying.             (line   6)
* counting lines:                        General Output Control.
                                                              (line   8)
* cx GREP_COLORS capability:             Environment Variables.
                                                              (line  85)
* default options environment variable:  Environment Variables.
                                                              (line  45)
* device search:                         File and Directory Selection.
                                                              (line  51)
* digit character class:                 Character Classes and Bracket Expressions.
                                                              (line  49)
* digit characters:                      Character Classes and Bracket Expressions.
                                                              (line  49)
* directory search:                      File and Directory Selection.
                                                              (line  62)
* dot:                                   Fundamental Structure.
                                                              (line  11)
* encoding error:                        Environment Variables.
                                                              (line 168)
* environment variables:                 Environment Variables.
                                                              (line  44)
* exclude directories:                   File and Directory Selection.
                                                              (line  87)
* exclude files:                         File and Directory Selection.
                                                              (line  73)
* exclude files <1>:                     File and Directory Selection.
                                                              (line  83)
* exit status:                           Exit Status.         (line   6)
* FAQ about grep usage:                  Usage.               (line  33)
* files which don’t match:               General Output Control.
                                                              (line  29)
* fn GREP_COLORS capability:             Environment Variables.
                                                              (line 124)
* fn GREP_COLORS capability <1>:         Environment Variables.
                                                              (line 139)
* graph character class:                 Character Classes and Bracket Expressions.
                                                              (line  52)
* graphic characters:                    Character Classes and Bracket Expressions.
                                                              (line  52)
* grep programs:                         grep Programs.       (line   6)
* GREP_COLOR environment variable:       Environment Variables.
                                                              (line  58)
* GREP_COLORS environment variable:      Environment Variables.
                                                              (line  69)
* GREP_OPTIONS environment variable:     Environment Variables.
                                                              (line  45)
* group separator:                       Context Line Control.
                                                              (line  27)
* group separator <1>:                   Context Line Control.
                                                              (line  31)
* hexadecimal digits:                    Character Classes and Bracket Expressions.
                                                              (line  76)
* highlight markers:                     Environment Variables.
                                                              (line  58)
* highlight markers <1>:                 Environment Variables.
                                                              (line  69)
* highlight, color, colour:              General Output Control.
                                                              (line  14)
* holes in files:                        Performance.         (line  42)
* include files:                         File and Directory Selection.
                                                              (line  97)
* interval specifications:               Basic vs Extended.   (line  10)
* invert matching:                       Matching Control.    (line  51)
* LANG environment variable:             Environment Variables.
                                                              (line   9)
* LANG environment variable <1>:         Environment Variables.
                                                              (line 161)
* LANG environment variable <2>:         Environment Variables.
                                                              (line 168)
* LANG environment variable <3>:         Environment Variables.
                                                              (line 190)
* LANGUAGE environment variable:         Environment Variables.
                                                              (line   9)
* LANGUAGE environment variable <1>:     Environment Variables.
                                                              (line 190)
* language of messages:                  Environment Variables.
                                                              (line 190)
* LC_ALL environment variable:           Environment Variables.
                                                              (line   9)
* LC_ALL environment variable <1>:       Environment Variables.
                                                              (line 161)
* LC_ALL environment variable <2>:       Environment Variables.
                                                              (line 168)
* LC_ALL environment variable <3>:       Environment Variables.
                                                              (line 190)
* LC_COLLATE environment variable:       Environment Variables.
                                                              (line 161)
* LC_CTYPE environment variable:         Environment Variables.
                                                              (line 168)
* LC_MESSAGES environment variable:      Environment Variables.
                                                              (line   9)
* LC_MESSAGES environment variable <1>:  Environment Variables.
                                                              (line 190)
* line buffering:                        Other Options.       (line  13)
* line numbering:                        Output Line Prefix Control.
                                                              (line  36)
* ln GREP_COLORS capability:             Environment Variables.
                                                              (line 129)
* locales:                               Performance.         (line  20)
* lower character class:                 Character Classes and Bracket Expressions.
                                                              (line  55)
* lower-case letters:                    Character Classes and Bracket Expressions.
                                                              (line  55)
* match expression at most M times:      Fundamental Structure.
                                                              (line  33)
* match expression at most once:         Fundamental Structure.
                                                              (line  18)
* match expression from N to M times:    Fundamental Structure.
                                                              (line  37)
* match expression N or more times:      Fundamental Structure.
                                                              (line  30)
* match expression N times:              Fundamental Structure.
                                                              (line  27)
* match expression one or more times:    Fundamental Structure.
                                                              (line  24)
* match expression zero or more times:   Fundamental Structure.
                                                              (line  21)
* match the whole line:                  Matching Control.    (line  73)
* matching basic regular expressions:    grep Programs.       (line  15)
* matching extended regular expressions: grep Programs.       (line  20)
* matching fixed strings:                grep Programs.       (line  25)
* matching Perl-compatible regular expressions: grep Programs.
                                                              (line  30)
* matching whole words:                  Matching Control.    (line  56)
* max-count:                             General Output Control.
                                                              (line  42)
* mc GREP_COLORS capability:             Environment Variables.
                                                              (line 116)
* message language:                      Environment Variables.
                                                              (line 190)
* ms GREP_COLORS capability:             Environment Variables.
                                                              (line 108)
* MS-Windows binary I/O:                 Other Options.       (line  18)
* mt GREP_COLORS capability:             Environment Variables.
                                                              (line 100)
* names of matching files:               General Output Control.
                                                              (line  35)
* national language support:             Environment Variables.
                                                              (line 161)
* national language support <1>:         Environment Variables.
                                                              (line 190)
* ne GREP_COLORS capability:             Environment Variables.
                                                              (line 146)
* NLS:                                   Environment Variables.
                                                              (line 161)
* no filename prefix:                    Output Line Prefix Control.
                                                              (line  23)
* null character:                        Environment Variables.
                                                              (line 168)
* numeric characters:                    Character Classes and Bracket Expressions.
                                                              (line  49)
* only matching:                         General Output Control.
                                                              (line  72)
* option delimiter:                      Other Options.       (line   7)
* patterns from file:                    Matching Control.    (line  17)
* patterns option:                       Matching Control.    (line   8)
* performance:                           Performance.         (line   6)
* period:                                Fundamental Structure.
                                                              (line  11)
* plus sign:                             Fundamental Structure.
                                                              (line  24)
* POSIXLY_CORRECT environment variable:  Environment Variables.
                                                              (line 195)
* print character class:                 Character Classes and Bracket Expressions.
                                                              (line  59)
* print non-matching lines:              Matching Control.    (line  51)
* printable characters:                  Character Classes and Bracket Expressions.
                                                              (line  59)
* punct character class:                 Character Classes and Bracket Expressions.
                                                              (line  62)
* punctuation characters:                Character Classes and Bracket Expressions.
                                                              (line  62)
* question mark:                         Fundamental Structure.
                                                              (line  18)
* quiet, silent:                         General Output Control.
                                                              (line  80)
* range expression:                      Character Classes and Bracket Expressions.
                                                              (line  14)
* recursive search:                      File and Directory Selection.
                                                              (line 102)
* recursive search <1>:                  File and Directory Selection.
                                                              (line 110)
* regular expressions:                   Regular Expressions. (line   6)
* return status:                         Exit Status.         (line   6)
* rv GREP_COLORS capability:             Environment Variables.
                                                              (line  94)
* searching directory trees:             File and Directory Selection.
                                                              (line  73)
* searching directory trees <1>:         File and Directory Selection.
                                                              (line  83)
* searching directory trees <2>:         File and Directory Selection.
                                                              (line  97)
* searching directory trees <3>:         File and Directory Selection.
                                                              (line 102)
* searching directory trees <4>:         File and Directory Selection.
                                                              (line 110)
* searching for patterns:                Introduction.        (line   6)
* sl GREP_COLORS capability:             Environment Variables.
                                                              (line  77)
* space character class:                 Character Classes and Bracket Expressions.
                                                              (line  67)
* space characters:                      Character Classes and Bracket Expressions.
                                                              (line  67)
* subexpression:                         Back-references and Subexpressions.
                                                              (line   6)
* suppress binary data:                  File and Directory Selection.
                                                              (line   8)
* suppress error messages:               General Output Control.
                                                              (line  87)
* symbolic links:                        File and Directory Selection.
                                                              (line  62)
* symbolic links <1>:                    File and Directory Selection.
                                                              (line 102)
* symbolic links <2>:                    File and Directory Selection.
                                                              (line 110)
* tab-aligned content lines:             Output Line Prefix Control.
                                                              (line  41)
* translation of message language:       Environment Variables.
                                                              (line 190)
* upper character class:                 Character Classes and Bracket Expressions.
                                                              (line  72)
* upper-case letters:                    Character Classes and Bracket Expressions.
                                                              (line  72)
* usage summary, printing:               Generic Program Information.
                                                              (line   7)
* usage, examples:                       Usage.               (line   6)
* using grep, Q&A:                       Usage.               (line  33)
* variants of grep:                      grep Programs.       (line   6)
* version, printing:                     Generic Program Information.
                                                              (line  12)
* whitespace characters:                 Character Classes and Bracket Expressions.
                                                              (line  67)
* with filename prefix:                  Output Line Prefix Control.
                                                              (line  18)
* xdigit character class:                Character Classes and Bracket Expressions.
                                                              (line  76)
* xdigit class:                          Character Classes and Bracket Expressions.
                                                              (line  76)
* zero-terminated file names:            Output Line Prefix Control.
                                                              (line  50)
* zero-terminated lines:                 Other Options.       (line  39)