This is grep.info, produced by makeinfo version 7.0dev from grep.texi.

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

Permission is granted to copy, distribute and/or modify this
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INFO-DIR-SECTION Text creation and manipulation
START-INFO-DIR-ENTRY
* grep: (grep). Print lines that match patterns.
END-INFO-DIR-ENTRY

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 3.11 of GNU Grep.

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

* 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. When FILE is ‘-’, read patterns
from standard input. 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
Special Backslash 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 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.
*Note Environment Variables::.

WHEN is ‘always’ to use colors, ‘never’ to not use colors, or
‘auto’ to use colors if standard output is associated with a
terminal device and the ‘TERM’ environment variable's value
suggests that the terminal supports colors. Plain ‘--color’ is
treated like ‘--color=auto’; if no ‘--color’ option is given, the
default is ‘--color=never’.

‘-L’
‘--files-without-match’
Suppress normal output; instead print the name of each input file
from which no output would normally have been printed.

‘-l’
‘--files-with-matches’
Suppress normal output; instead print the name of each input file
from which output would normally have been printed. Scanning each
input file stops upon first match. (‘-l’ is specified by POSIX.)

‘-m NUM’
‘--max-count=NUM’
Stop after the first NUM selected lines. If NUM is zero, ‘grep’
stops right away without reading input. A NUM of −1 is treated as
infinity and ‘grep’ does not stop; this is the default.

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.
Portability note: Solaris 10 ‘grep’ lacks ‘-q’; portable shell
scripts typically can redirect standard output to ‘/dev/null’
instead of using ‘-q’. (‘-q’ is specified by POSIX.)

‘-s’
‘--no-messages’
Suppress error messages about nonexistent or unreadable files.
(‘-s’ is specified by POSIX.)

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 message to standard
error 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’. If contradictory ‘--include’ and
‘--exclude’ options are given, the last matching one wins. If no
‘--include’ or ‘--exclude’ options match, a file is included unless
the first such option is ‘--include’.

‘-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 for standard output, regardless of output
device. By default, standard output is line buffered for
interactive devices, and is fully buffered otherwise. With full
buffering, the output buffer is flushed when full; with line
buffering, the buffer is also flushed after every output line. The
buffer size is system dependent.

‘-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 several environment variables, the
most important of which control the locale, which specifies how ‘grep’
interprets characters in its patterns and data.

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.UTF-8’, then a 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.

The following environment variables affect the behavior of ‘grep’.

‘GREP_COLOR’
This obsolescent variable interacts with ‘GREP_COLORS’ confusingly,
and ‘grep’ warns if it is set and is not overridden by
‘GREP_COLORS’. Instead of ‘GREP_COLOR='COLOR'’, you can use
‘GREP_COLORS='mt=COLOR'’.

‘GREP_COLORS’
This variable controls how the ‘--color’ option highlights 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).
The two-letter capability names 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. Non-empty capability values
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.

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.
*Note Character Encoding::.

‘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.

‘TERM’
This variable specifies the output terminal type, which can affect
what the ‘--color’ option does. *Note General Output Control::.

The ‘GREP_OPTIONS’ environment variable of ‘grep’ 2.20 and earlier is
no longer supported, as it caused problems when writing portable
scripts. To make arbitrary changes to how ‘grep’ works, you can 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 "$@"

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 ‘-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::.

For documentation, refer to <https://www.pcre.org/>, with these
caveats:
• ‘\d’ matches only the ten ASCII digits (and ‘\D’ matches the
complement), regardless of locale. Use ‘\p{Nd}’ to also match
non-ASCII digits. (The behavior of ‘\d’ and ‘\D’ is
unspecified after in-regexp directives like ‘(?aD)’.)

• Although PCRE tracks the syntax and semantics of Perl's
regular expressions, the match is not always exact. For
example, Perl evolves and a Perl installation may predate or
postdate the PCRE2 installation on the same host, or their
Unicode versions may differ, or Perl and PCRE2 may disagree
about an obscure construct.

• By default, ‘grep’ applies each regexp to a line at a time, so
the ‘(?s)’ directive (making ‘.’ match line breaks) is
generally ineffective. However, with ‘-z’ (‘--null-data’) it
can work:
$ printf 'a\nb\n' |grep -zP '(?s)a.b'
a
b
But beware: with the ‘-z’ (‘--null-data’) and a file
containing no NUL byte, grep must read the entire file into
memory before processing any of it. Thus, it will exhaust
memory and fail for some large files.

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’, basic and extended regular expressions are merely different
notations for the same pattern-matching functionality. In other
implementations, basic regular expressions are ordinarily less powerful
than extended, though occasionally it is the other way around. The
following description applies to extended regular expressions;
differences for basic regular expressions are summarized afterwards.
Perl-compatible regular expressions have different functionality, and
are documented in the pcre2syntax(3) and pcre2pattern(3) manual pages,
but work only if PCRE is available in the system.

* Menu:

* Fundamental Structure::
* Character Classes and Bracket Expressions::
* Special Backslash Expressions::
* Anchoring::
* Back-references and Subexpressions::
* Basic vs Extended::
* Problematic Expressions::
* Character Encoding::
* Matching Non-ASCII::

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

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

In regular expressions, the characters ‘.?*+{|()[\^$’ are “special
characters” and have uses described below. All other characters are
“ordinary characters”, and each ordinary character is a regular
expression that matches itself.

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 operators beginning with ‘{’ are called “interval
expressions”.

‘?’
The preceding item is optional and is matched at most once.

‘*’
The preceding item is matched zero or more times.

‘+’
The preceding item is 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 of the
two expressions, which are called “alternatives”.

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.

Not every character string is a valid regular expression. *Note
Problematic Expressions::.

File: grep.info, Node: Character Classes and Bracket Expressions, Next: Special Backslash 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 be erratic, or it might be invalid. 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 regular
expression ‘[:epru]’.

Special 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. To make the ‘-’ a list item, it is best
to put it last.

‘^’
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: Special Backslash Expressions, Next: Anchoring, Prev: Character Classes and Bracket Expressions, Up: Regular Expressions

3.3 Special Backslash Expressions
=================================

The ‘\’ character followed by a special character is a regular
expression that matches the special character. 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 a word.

‘\>’
Match the empty string at the end of a 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:]]’.

‘\]’
Match ‘]’.

‘\}’
Match ‘}’.

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

The behavior of ‘grep’ is unspecified if a unescaped backslash is not
followed by a special character, a nonzero digit, or a character in the
above list. Although ‘grep’ might issue a diagnostic and/or give the
backslash an interpretation now, its behavior may change if the syntax
of regular expressions is extended in future versions.

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

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

The caret ‘^’ and the dollar sign ‘$’ are special 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 nonzero digit, matches the
substring previously matched by the Nth parenthesized subexpression of
the regular expression. For example, ‘(a)\1’ matches ‘aa’. If the
parenthesized subexpression does not participate in the match, the
back-reference makes the whole match fail; for example, ‘(a)*\1’ fails
to match ‘a’. If the parenthesized subexpression matches more than one
substring, the back-reference refers to the last matched substring; for
example, ‘^(ab*)*\1$’ matches ‘ababbabb’ but not ‘ababbab’. 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, Next: Problematic Expressions, Prev: Back-references and Subexpressions, Up: Regular Expressions

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

Basic regular expressions differ from extended regular expressions in
the following ways:

• The characters ‘?’, ‘+’, ‘{’, ‘|’, ‘(’, and ‘)’ lose their special
meaning; instead use the backslashed versions ‘\?’, ‘\+’, ‘\{’,
‘\|’, ‘$’, and ‘$’. Also, a backslash is needed before an
interval expression's closing ‘}’.

• An unmatched ‘\)’ is invalid.

• If an unescaped ‘^’ appears neither first, nor directly after ‘\(’
or ‘\|’, it is treated like an ordinary character and is not an
anchor.

• If an unescaped ‘$’ appears neither last, nor directly before ‘\|’
or ‘\)’, it is treated like an ordinary character and is not an
anchor.

• If an unescaped ‘*’ appears first, or appears directly after ‘\(’
or ‘\|’ or anchoring ‘^’, it is treated like an ordinary character
and is not a repetition operator.

File: grep.info, Node: Problematic Expressions, Next: Character Encoding, Prev: Basic vs Extended, Up: Regular Expressions

3.7 Problematic Regular Expressions
===================================

Some strings are “invalid regular expressions” and cause ‘grep’ to issue
a diagnostic and fail. For example, ‘xy\1’ is invalid because there is
no parenthesized subexpression for the back-reference ‘\1’ to refer to.

Also, some regular expressions have “unspecified behavior” and should
be avoided even if ‘grep’ does not currently diagnose them. For
example, ‘xy\0’ has unspecified behavior because ‘0’ is not a special
character and ‘\0’ is not a special backslash expression (*note Special
Backslash Expressions::). Unspecified behavior can be particularly
problematic because the set of matched strings might be only partially
specified, or not be specified at all, or the expression might even be
invalid.

The following regular expression constructs are invalid on all
platforms conforming to POSIX, so portable scripts can assume that
‘grep’ rejects these constructs:

• A basic regular expression containing a back-reference ‘\N’
preceded by fewer than N closing parentheses. For example,
‘$a$\2’ is invalid.

• A bracket expression containing ‘[:’ that does not start a
character class; and similarly for ‘[=’ and ‘[.’. For example,
‘[a[:b]’ and ‘[a[:ouch:]b]’ are invalid.

GNU ‘grep’ treats the following constructs as invalid. However,
other ‘grep’ implementations might allow them, so portable scripts
should not rely on their being invalid:

• Unescaped ‘\’ at the end of a regular expression.

• Unescaped ‘[’ that does not start a bracket expression.

• A ‘\{’ in a basic regular expression that does not start an
interval expression.

• A basic regular expression with unbalanced ‘$’ or ‘$’, or an
extended regular expression with unbalanced ‘(’.

• In the POSIX locale, a range expression like ‘z-a’ that represents
zero elements. A non-GNU ‘grep’ might treat it as a valid range
that never matches.

• An interval expression with a repetition count greater than 32767.
(The portable POSIX limit is 255, and even interval expressions
with smaller counts can be impractically slow on all known
implementations.)

• A bracket expression that contains at least three elements, the
first and last of which are both ‘:’, or both ‘.’, or both ‘=’.
For example, a non-GNU ‘grep’ might treat ‘[:alpha:]’ like
‘[[:alpha:]]’, or like ‘[:ahlp]’.

The following constructs have well-defined behavior in GNU ‘grep’.
However, they have unspecified behavior elsewhere, so portable scripts
should avoid them:

• Special backslash expressions like ‘\b’, ‘\<’, and ‘\]’. *Note
Special Backslash Expressions::.

• A basic regular expression that uses ‘\?’, ‘\+’, or ‘\|’.

• An extended regular expression that uses back-references.

• An empty regular expression, subexpression, or alternative. For
example, ‘(a|bc|)’ is not portable; a portable equivalent is
‘(a|bc)?’.

• In a basic regular expression, an anchoring ‘^’ that appears
directly after ‘$’, or an anchoring ‘$’ that appears directly
before ‘$’.

• In a basic regular expression, a repetition operator that directly
follows another repetition operator.

• In an extended regular expression, unescaped ‘{’ that does not
begin a valid interval expression. GNU ‘grep’ treats the ‘{’ as an
ordinary character.

• A null character or an encoding error in either pattern or input
data. *Note Character Encoding::.

• An input file that ends in a non-newline character, where GNU
‘grep’ silently supplies a newline.

The following constructs have unspecified behavior, in both GNU and
other ‘grep’ implementations. Scripts should avoid them whenever
possible.

• A backslash escaping an ordinary character, unless it is a
back-reference like ‘\1’ or a special backslash expression like
‘\<’ or ‘\b’. *Note Special Backslash Expressions::. For example,
‘\x’ has unspecified behavior now, and a future version of ‘grep’
might specify ‘\x’ to have a new behavior.

• A repetition operator that appears directly after an anchor, or at
the start of a complete regular expression, parenthesized
subexpression, or alternative. For example, ‘+|^*(+a|?-b)’ has
unspecified behavior, whereas ‘\+|^\*(\+a|\?-b)’ is portable.

• A range expression outside the POSIX locale. For example, in some
locales ‘[a-z]’ might match some characters that are not lowercase
letters, or might not match some lowercase letters, or might be
invalid. With GNU ‘grep’ it is not documented whether these range
expressions use native code points, or use the collating sequence
specified by the ‘LC_COLLATE’ category, or have some other
interpretation. Outside the POSIX locale, it is portable to use
‘[[:lower:]]’ to match a lower-case letter, or
‘[abcdefghijklmnopqrstuvwxyz]’ to match an ASCII lower-case letter.

File: grep.info, Node: Character Encoding, Next: Matching Non-ASCII, Prev: Problematic Expressions, Up: Regular Expressions

3.8 Character Encoding
======================

The ‘LC_CTYPE’ locale specifies the encoding of characters in patterns
and data, that is, whether text is encoded in UTF-8, ASCII, or some
other encoding. *Note Environment Variables::.

In the ‘C’ or ‘POSIX’ locale, every character is 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::.

Regardless of locale, the 103 characters in the POSIX Portable
Character Set (a subset of ASCII) are always encoded as a single byte,
and the 128 ASCII characters have their usual single-byte encodings on
all but oddball platforms.

File: grep.info, Node: Matching Non-ASCII, Prev: Character Encoding, Up: Regular Expressions

3.9 Matching Non-ASCII and Non-printable Characters
===================================================

In a regular expression, non-ASCII and non-printable characters other
than newline are not special, and represent themselves. For example, in
a locale using UTF-8 the command ‘grep 'Λ ω'’ (where the white space
between ‘Λ’ and the ‘ω’ is a tab character) searches for ‘Λ’ (Unicode
character U+039B GREEK CAPITAL LETTER LAMBDA), followed by a tab (U+0009
TAB), followed by ‘ω’ (U+03C9 GREEK SMALL LETTER OMEGA).

Suppose you want to limit your pattern to only printable characters
(or even only printable ASCII characters) to keep your script readable
or portable, but you also want to match specific non-ASCII or non-null
non-printable characters. If you are using the ‘-P’ (‘--perl-regexp’)
option, PCREs give you several ways to do this. Otherwise, if you are
using Bash, the GNU project's shell, you can represent these characters
via ANSI-C quoting. For example, the Bash commands ‘grep $'Λ\tω'’ and
‘grep $'\u039B\t\u03C9'’ both search for the same three-character string
‘Λ ω’ mentioned earlier. However, because Bash translates ANSI-C
quoting before ‘grep’ sees the pattern, this technique should not be
used to match printable ASCII characters; for example, ‘grep $'\u005E'’
is equivalent to ‘grep '^'’ and matches any line, not just lines
containing the character ‘^’ (U+005E CIRCUMFLEX ACCENT).

Since PCREs and ANSI-C quoting are GNU extensions to POSIX, portable
shell scripts written in ASCII should use other methods to match
specific non-ASCII characters. For example, in a UTF-8 locale the
command ‘grep "$(printf '\316\233\t\317\211\n')"’ is a portable albeit
hard-to-read alternative to Bash's ‘grep $'Λ\tω'’. However, none of
these techniques will let you put a null character directly into a
command-line pattern; null characters can appear only in a pattern
specified via the ‘-f’ (‘--file’) option.

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, showing the location and contents of
any line containing ‘f’ and ending in ‘.c’, within all files in the
current directory whose names start with non-‘.’, contain ‘g’, and end
in ‘.h’. The ‘-n’ option outputs line numbers, the ‘--’ argument treats
any later arguments as file names not options even if ‘*g*.h’ expands to
a file name that starts with ‘-’, 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

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 ‘-’? For example:

grep "$pattern" *

can behave unexpectedly if the value of ‘pattern’ begins with ‘-’,
or if the ‘*’ expands to a file name with leading ‘-’. To avoid
the problem, you can use ‘-e’ for patterns and leading ‘./’ for
files:

grep -e "$pattern" ./*

searches for all lines matching the pattern in all the working
directory's files whose names do not begin with ‘.’. Without the
‘-e’, ‘grep’ might treat the pattern as an option if it begins with
‘-’. Without the ‘./’, there might be similar problems with file
names beginning with ‘-’.

Alternatively, you can use ‘--’ before the pattern and file names:

grep -- "$pattern" *

This also fixes the problem, except that if there is a file named
‘-’, ‘grep’ misinterprets the ‘-’ as standard input.

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 an
extended regular expression like ‘a^’ or ‘$a’. To match every
line, a portable script should use a pattern like ‘^’ instead of
the empty pattern, as POSIX does not specify the behavior of the
empty pattern.

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 can't I combine the shell's ‘set -e’ with ‘grep’?

The ‘grep’ command follows the convention of programs like ‘cmp’
and ‘diff’ where an exit status of 1 is not an error. The shell
command ‘set -e’ causes the shell to exit if any subcommand exits
with nonzero status, and this will cause the shell to exit merely
because ‘grep’ selected no lines, which is ordinarily not what you
want.

There is a related problem with Bash's ‘set -e -o pipefail’. Since
‘grep’ does not always read all its input, a command outputting to
a pipe read by ‘grep’ can fail when ‘grep’ exits before reading all
its input, and the command's failure can cause Bash to exit.

14. Why is this back-reference failing?

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

This outputs an error message, because the second ‘\1’ has nothing
to refer back to, meaning it will never match anything.

15. 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.

16. What do ‘grep’, ‘-E’, and ‘-F’ 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

The ‘-E’ option stands for Extended ‘grep’. The ‘-F’ option stands
for Fixed ‘grep’;

17. What happened to ‘egrep’ and ‘fgrep’?

7th Edition Unix had commands ‘egrep’ and ‘fgrep’ that were the
counterparts of the modern ‘grep -E’ and ‘grep -F’. Although
breaking up ‘grep’ into three programs was perhaps useful on the
small computers of the 1970s, ‘egrep’ and ‘fgrep’ were deemed
obsolescent by POSIX in 1992, removed from POSIX in 2001,
deprecated by GNU Grep 2.5.3 in 2007, and changed to issue
obsolescence warnings by GNU Grep 3.8 in 2022; eventually, they are
planned to be removed entirely.

If you prefer the old names, you can use your own substitutes, such
as a shell script named ‘egrep’ with the following contents:

#!/bin/sh
exec grep -E "$@"

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.

Interval expressions may be implemented internally via repetition.
For example, ‘^(a|bc){2,4}$’ might be implemented as
‘^(a|bc)(a|bc)((a|bc)(a|bc)?)?$’. A large repetition count may exhaust
memory or greatly slow matching. Even small counts can cause problems
if cascaded; for example, ‘grep -E ".*{10,}{10,}{10,}{10,}{10,}"’ is
likely to overflow a stack. Fortunately, regular expressions like these
are typically artificial, and cascaded repetitions do not conform to
POSIX so cannot be used in portable programs anyway.

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 efficiency ‘grep’ does not always read all its input. For
example, the shell command ‘sed '/^...$/d' | grep -q X’ can cause ‘grep’
to exit immediately after reading a line containing ‘X’, without
bothering to read the rest of its input data. This in turn can cause
‘sed’ to exit with a nonzero status because ‘sed’ cannot write to its
output pipe after ‘grep’ exits.

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://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://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://doi.org/10.1145/2431211.2431212>. This
surveys string matching algorithms that might help improve the
performance of ‘grep’ in the future.

• Hakak SI, Kamsin A, Shivakumara P, Gilkar GA, Khan WZ, Imran M.
Exact string matching algorithms: survey issues, and future
research directions. _IEEE Access_. 2019;7:69614-37.
<https://doi.org/10.1109/ACCESS.2019.2914071>. This survey is more
recent than Faro & Lecroq, and focuses on taxonomy instead of
performance.

• Hume A, Sunday D. Fast string search. _Software Pract Exper_.
1991;21(11):1221-48. <https://doi.org/10.1002/spe.4380211105>. This
excellent albeit now-dated survey aided the initial development of
‘grep’.

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 2021 the GNU C library bug database
(https://sourceware.org/bugzilla/) contained back-reference bugs 52,
10844, 11053, 24269 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

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
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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
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"Document", below, refers to any such manual or work. Any member
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A "Modified Version" of the Document means any work containing the
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A "Secondary Section" is a named appendix or a front-matter section
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The "Invariant Sections" are certain Secondary Sections whose
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The "Cover Texts" are certain short passages of text that are
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A "Transparent" copy of the Document means a machine-readable copy,
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The "publisher" means any person or entity that distributes copies
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To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
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The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
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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
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may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
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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
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these Cover Texts: Front-Cover Texts on the front cover, and
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conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit
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reasonably) on the actual cover, and continue the rest onto
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If you publish or distribute Opaque copies of the Document
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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
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Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever
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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
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History section of the Document). You may use the same title
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B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
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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
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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
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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
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O. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or
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You may add a section Entitled "Endorsements", provided it contains
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You may combine the Document with other documents released under
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In the combination, you must combine any sections Entitled
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Entitled "History"; likewise combine any sections Entitled
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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
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storage or distribution medium, is called an "aggregate" if the
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legal rights of the compilation's users beyond what the individual
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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
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electronic equivalent of covers if the Document is in electronic
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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
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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
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finally terminates your license, and (b) permanently, if the
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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
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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/licenses/>.

Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
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have the option of following the terms and conditions either of
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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
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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.

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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
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their use in free software.

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

Index
*****

[index]
* Menu:

* --: 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 22)
* --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 113)
* --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 38)
* --files-without-match: General Output Control.
(line 33)
* --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 44)
* --no-filename: Output Line Prefix Control.
(line 23)
* --no-ignore-case: Matching Control. (line 44)
* --no-messages: General Output Control.
(line 95)
* --null: Output Line Prefix Control.
(line 50)
* --null-data: Other Options. (line 43)
* --only-matching: General Output Control.
(line 78)
* --perl-regexp: grep Programs. (line 30)
* --quiet: General Output Control.
(line 86)
* --recursive: File and Directory Selection.
(line 105)
* --regexp=PATTERNS: Matching Control. (line 8)
* --silent: General Output Control.
(line 86)
* --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 33)
* -l: General Output Control.
(line 38)
* -m: General Output Control.
(line 44)
* -n: Output Line Prefix Control.
(line 36)
* -NUM: Context Line Control.
(line 24)
* -o: General Output Control.
(line 78)
* -P: grep Programs. (line 30)
* -q: General Output Control.
(line 86)
* -r: File and Directory Selection.
(line 105)
* -R: File and Directory Selection.
(line 113)
* -s: General Output Control.
(line 95)
* -T: Output Line Prefix Control.
(line 41)
* -U: Other Options. (line 22)
* -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 43)
* ?: Fundamental Structure.
(line 19)
* .: Fundamental Structure.
(line 11)
* {,M}: Fundamental Structure.
(line 34)
* {N,}: Fundamental Structure.
(line 31)
* {N,M}: Fundamental Structure.
(line 38)
* {N}: Fundamental Structure.
(line 28)
* *: Fundamental Structure.
(line 22)
* +: Fundamental Structure.
(line 25)
* after context: Context Line Control.
(line 15)
* alnum character class: Character Classes and Bracket Expressions.
(line 32)
* alpha character class: Character Classes and Bracket Expressions.
(line 37)
* alphabetic characters: Character Classes and Bracket Expressions.
(line 37)
* alphanumeric characters: Character Classes and Bracket Expressions.
(line 32)
* alternatives in regular expressions: Fundamental Structure.
(line 46)
* anchoring: Anchoring. (line 6)
* asterisk: Fundamental Structure.
(line 22)
* back-reference: Back-references and Subexpressions.
(line 6)
* back-references: Performance. (line 41)
* backslash: Special Backslash 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 22)
* blank character class: Character Classes and Bracket Expressions.
(line 42)
* blank characters: Character Classes and Bracket Expressions.
(line 42)
* bn GREP_COLORS capability: Environment Variables.
(line 117)
* braces, first argument omitted: Fundamental Structure.
(line 34)
* braces, one argument: Fundamental Structure.
(line 28)
* braces, second argument omitted: Fundamental Structure.
(line 31)
* braces, two arguments: Fundamental Structure.
(line 38)
* 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 31)
* character encoding: Character Encoding. (line 6)
* character type: Environment Variables.
(line 144)
* classes of characters: Character Classes and Bracket Expressions.
(line 31)
* cntrl character class: Character Classes and Bracket Expressions.
(line 45)
* context lines: General Output Control.
(line 70)
* 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 45)
* copying: Copying. (line 6)
* counting lines: General Output Control.
(line 8)
* cx GREP_COLORS capability: Environment Variables.
(line 68)
* device search: File and Directory Selection.
(line 51)
* digit character class: Character Classes and Bracket Expressions.
(line 50)
* digit characters: Character Classes and Bracket Expressions.
(line 50)
* directory search: File and Directory Selection.
(line 62)
* dot: Fundamental Structure.
(line 11)
* encoding error: Environment Variables.
(line 151)
* environment variables: Environment Variables.
(line 24)
* 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 32)
* files which don't match: General Output Control.
(line 33)
* fn GREP_COLORS capability: Environment Variables.
(line 107)
* fn GREP_COLORS capability <1>: Environment Variables.
(line 122)
* graph character class: Character Classes and Bracket Expressions.
(line 53)
* graphic characters: Character Classes and Bracket Expressions.
(line 53)
* grep programs: grep Programs. (line 6)
* GREP_COLOR environment variable: Environment Variables.
(line 27)
* GREP_COLORS environment variable: Environment Variables.
(line 33)
* group separator: Context Line Control.
(line 27)
* group separator <1>: Context Line Control.
(line 31)
* hexadecimal digits: Character Classes and Bracket Expressions.
(line 77)
* highlight markers: Environment Variables.
(line 27)
* highlight markers <1>: Environment Variables.
(line 33)
* highlight, color, colour: General Output Control.
(line 14)
* holes in files: Performance. (line 51)
* include files: File and Directory Selection.
(line 97)
* interval expressions: Fundamental Structure.
(line 14)
* interval expressions <1>: Performance. (line 32)
* invalid regular expressions: Problematic Expressions.
(line 6)
* invert matching: Matching Control. (line 51)
* LANG environment variable: Environment Variables.
(line 10)
* LANG environment variable <1>: Environment Variables.
(line 144)
* LANG environment variable <2>: Environment Variables.
(line 151)
* LANG environment variable <3>: Environment Variables.
(line 160)
* LANGUAGE environment variable: Environment Variables.
(line 10)
* LANGUAGE environment variable <1>: Environment Variables.
(line 160)
* language of messages: Environment Variables.
(line 160)
* LC_ALL environment variable: Environment Variables.
(line 10)
* LC_ALL environment variable <1>: Environment Variables.
(line 144)
* LC_ALL environment variable <2>: Environment Variables.
(line 151)
* LC_ALL environment variable <3>: Environment Variables.
(line 160)
* LC_COLLATE environment variable: Environment Variables.
(line 144)
* LC_CTYPE environment variable: Environment Variables.
(line 151)
* LC_MESSAGES environment variable: Environment Variables.
(line 10)
* LC_MESSAGES environment variable <1>: Environment Variables.
(line 160)
* line buffering: Other Options. (line 13)
* line numbering: Output Line Prefix Control.
(line 36)
* ln GREP_COLORS capability: Environment Variables.
(line 112)
* locales: Performance. (line 20)
* lower character class: Character Classes and Bracket Expressions.
(line 56)
* lower-case letters: Character Classes and Bracket Expressions.
(line 56)
* match expression at most M times: Fundamental Structure.
(line 34)
* match expression at most once: Fundamental Structure.
(line 19)
* match expression from N to M times: Fundamental Structure.
(line 38)
* match expression N or more times: Fundamental Structure.
(line 31)
* match expression N times: Fundamental Structure.
(line 28)
* match expression one or more times: Fundamental Structure.
(line 25)
* match expression zero or more times: Fundamental Structure.
(line 22)
* 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 44)
* mc GREP_COLORS capability: Environment Variables.
(line 99)
* message language: Environment Variables.
(line 160)
* ms GREP_COLORS capability: Environment Variables.
(line 91)
* MS-Windows binary I/O: Other Options. (line 22)
* mt GREP_COLORS capability: Environment Variables.
(line 83)
* names of matching files: General Output Control.
(line 38)
* national language support: Environment Variables.
(line 144)
* national language support <1>: Environment Variables.
(line 160)
* ne GREP_COLORS capability: Environment Variables.
(line 129)
* NLS: Environment Variables.
(line 144)
* no filename prefix: Output Line Prefix Control.
(line 23)
* non-ASCII matching: Matching Non-ASCII. (line 6)
* non-printable matching: Matching Non-ASCII. (line 6)
* null character: Environment Variables.
(line 151)
* numeric characters: Character Classes and Bracket Expressions.
(line 50)
* only matching: General Output Control.
(line 78)
* option delimiter: Other Options. (line 7)
* ordinary characters: Fundamental Structure.
(line 6)
* patterns from file: Matching Control. (line 17)
* patterns option: Matching Control. (line 8)
* performance: Performance. (line 6)
* period: Fundamental Structure.
(line 11)
* pipelines and reading: Performance. (line 59)
* plus sign: Fundamental Structure.
(line 25)
* POSIXLY_CORRECT environment variable: Environment Variables.
(line 165)
* print character class: Character Classes and Bracket Expressions.
(line 60)
* print non-matching lines: Matching Control. (line 51)
* printable characters: Character Classes and Bracket Expressions.
(line 60)
* punct character class: Character Classes and Bracket Expressions.
(line 63)
* punctuation characters: Character Classes and Bracket Expressions.
(line 63)
* question mark: Fundamental Structure.
(line 19)
* quiet, silent: General Output Control.
(line 86)
* range expression: Character Classes and Bracket Expressions.
(line 14)
* recursive search: File and Directory Selection.
(line 105)
* recursive search <1>: File and Directory Selection.
(line 113)
* regular expressions: Regular Expressions. (line 6)
* return status: Exit Status. (line 6)
* rv GREP_COLORS capability: Environment Variables.
(line 77)
* 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 105)
* searching directory trees <4>: File and Directory Selection.
(line 113)
* searching for patterns: Introduction. (line 6)
* sl GREP_COLORS capability: Environment Variables.
(line 60)
* space character class: Character Classes and Bracket Expressions.
(line 68)
* space characters: Character Classes and Bracket Expressions.
(line 68)
* special characters: Fundamental Structure.
(line 6)
* subexpression: Back-references and Subexpressions.
(line 6)
* suppress binary data: File and Directory Selection.
(line 8)
* suppress error messages: General Output Control.
(line 95)
* symbolic links: File and Directory Selection.
(line 62)
* symbolic links <1>: File and Directory Selection.
(line 105)
* symbolic links <2>: File and Directory Selection.
(line 113)
* tab-aligned content lines: Output Line Prefix Control.
(line 41)
* TERM environment variable: Environment Variables.
(line 172)
* translation of message language: Environment Variables.
(line 160)
* unspecified behavior in regular expressions: Problematic Expressions.
(line 6)
* upper character class: Character Classes and Bracket Expressions.
(line 73)
* upper-case letters: Character Classes and Bracket Expressions.
(line 73)
* usage summary, printing: Generic Program Information.
(line 7)
* usage, examples: Usage. (line 6)
* using grep, Q&A: Usage. (line 32)
* variants of grep: grep Programs. (line 6)
* version, printing: Generic Program Information.
(line 12)
* whitespace characters: Character Classes and Bracket Expressions.
(line 68)
* with filename prefix: Output Line Prefix Control.
(line 18)
* xdigit character class: Character Classes and Bracket Expressions.
(line 77)
* xdigit class: Character Classes and Bracket Expressions.
(line 77)
* zero-terminated file names: Output Line Prefix Control.
(line 50)
* zero-terminated lines: Other Options. (line 43)

Tag Table:
Node: Top769
Node: Introduction1954
Node: Invoking2697
Node: Command-line Options3540
Node: Generic Program Information4423
Node: Matching Control4897
Node: General Output Control8530
Node: Output Line Prefix Control12638
Node: Context Line Control14992
Node: File and Directory Selection17055
Node: Other Options22854
Node: Environment Variables25059
Node: Exit Status34261
Node: grep Programs34739
Node: Regular Expressions37411
Node: Fundamental Structure38759
Node: Character Classes and Bracket Expressions40779
Node: Special Backslash Expressions45606
Node: Anchoring47151
Node: Back-references and Subexpressions47591
Node: Basic vs Extended48595
Node: Problematic Expressions49800
Node: Character Encoding55243
Node: Matching Non-ASCII56715
Node: Usage58838
Node: Performance68662
Node: Reporting Bugs73869
Node: Known Bugs74246
Node: Copying75317
Node: GNU Free Documentation License76423
Node: Index101530

End Tag Table

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coding: utf-8
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