.\" GNU grep man page
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.	if !\w|\*(lq| \{\
.		ds lq ``
.		if \w'\(lq' .ds lq "\(lq
.	\}
.	if !\w|\*(rq| \{\
.		ds rq ''
.		if \w'\(rq' .ds rq "\(rq
.	\}
.\}
.
.ie \n[.g] .mso www.tmac
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.
.TH GREP 1 \*(Dt "GNU grep 3.1" "User Commands"
.hy 0
.
.SH NAME
grep, egrep, fgrep \- print lines matching a pattern
.
.SH SYNOPSIS
.B grep
.RI [ OPTIONS ]
.I PATTERN
.RI [ FILE .\|.\|.]
.br
.B grep
.RI [ OPTIONS ]
.B \-e
.I PATTERN
\&.\|.\|.\&
.RI [ FILE .\|.\|.]
.br
.B grep
.RI [ OPTIONS ]
.B \-f
.I FILE
\&.\|.\|.\&
.RI [ FILE .\|.\|.]
.
.SH DESCRIPTION
.B grep
searches for
.I PATTERN
in each
.IR FILE .
A
.I FILE
of
.RB "\*(lq" \- "\*(rq"
stands for standard input.
If no
.I FILE
is given, recursive searches examine the working directory,
and nonrecursive searches read standard input.
By default,
.B grep
prints the matching lines.
.PP
In addition, the variant programs
.B egrep
and
.B fgrep
are the same as
.B "grep\ \-E"
and
.BR "grep\ \-F" ,
respectively.
These variants are deprecated, but are provided for backward compatibility.
.
.SH OPTIONS
.SS "Generic Program Information"
.TP
.B \-\^\-help
Output a usage message and exit.
.TP
.BR \-V ", " \-\^\-version
Output the version number of
.B grep
and exit.
.SS "Matcher Selection"
.TP
.BR \-E ", " \-\^\-extended\-regexp
Interpret
.I PATTERN
as an extended regular expression (ERE, see below).
.TP
.BR \-F ", " \-\^\-fixed\-strings
Interpret
.I PATTERN
as a list of fixed strings (instead of regular expressions),
separated by newlines,
any of which is to be matched.
.TP
.BR \-G ", " \-\^\-basic\-regexp
Interpret
.I PATTERN
as a basic regular expression (BRE, see below).
This is the default.
.TP
.BR \-P ", " \-\^\-perl\-regexp
Interpret the pattern as a Perl-compatible regular expression (PCRE).
This is experimental and
.B "grep \-P"
may warn of unimplemented features.
.SS "Matching Control"
.TP
.BI \-e " PATTERN" "\fR,\fP \-\^\-regexp=" PATTERN
Use
.I PATTERN
as the pattern.
If this option is used multiple times or is combined with the
.B \-f
.RB ( \-\-file )
option, search for all patterns given.
This option can be used to protect a pattern beginning with \*(lq\-\*(rq.
.TP
.BI \-f " FILE" "\fR,\fP \-\^\-file=" FILE
Obtain patterns from
.IR FILE ,
one per line.
If this option is used multiple times or is combined with the
.B \-e
.RB ( \-\-regexp )
option, search for all patterns given.
The empty file contains zero patterns, and therefore matches nothing.
.TP
.BR \-i ", " \-\^\-ignore\-case
Ignore case distinctions, so that characters that differ only in case
match each other.
.TP
.BR \-v ", " \-\^\-invert\-match
Invert the sense of matching, to select non-matching lines.
.TP
.BR \-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
.B \-x
is also specified.
.TP
.BR \-x ", " \-\^\-line\-regexp
Select only those matches that exactly match the whole line.
For a regular expression pattern, this is like parenthesizing the
pattern and then surrounding it with
.B ^
and
.BR $ .
.TP
.B \-y
Obsolete synonym for
.BR \-i .
.SS "General Output Control"
.TP
.BR \-c ", " \-\^\-count
Suppress normal output; instead print a count of
matching lines for each input file.
With the
.BR \-v ", " \-\^\-invert\-match
option (see below), count non-matching lines.
.TP
.BR \-\^\-color [ =\fIWHEN\fP "], " \-\^\-colour [ =\fIWHEN\fP ]
Surround the matched (non-empty) strings, matching lines, context lines,
file names, line numbers, byte offsets, and separators (for fields and
groups of context lines) with escape sequences to display them in color
on the terminal.
The colors are defined by the environment variable
.BR GREP_COLORS .
The deprecated environment variable
.B GREP_COLOR
is still supported, but its setting does not have priority.
.I WHEN
is
.BR never ", " always ", or " auto .
.TP
.BR \-L ", " \-\^\-files\-without\-match
Suppress normal output; instead print the name
of each input file from which no output would
normally have been printed.
The scanning will stop on the first match.
.TP
.BR \-l ", " \-\^\-files\-with\-matches
Suppress normal output; instead print
the name of each input file from which output
would normally have been printed.
The scanning will stop on the first match.
.TP
.BI \-m " NUM" "\fR,\fP \-\^\-max\-count=" NUM
Stop reading a file after
.I NUM
matching lines.
If the input is standard input from a regular file,
and
.I NUM
matching lines are output,
.B grep
ensures that the standard input is positioned to just after the last
matching line before exiting, regardless of the presence of trailing
context lines.
This enables a calling process to resume a search.
When
.B grep
stops after
.I NUM
matching lines, it outputs any trailing context lines.
When the
.B \-c
or
.B \-\^\-count
option is also used,
.B grep
does not output a count greater than
.IR NUM .
When the
.B \-v
or
.B \-\^\-invert\-match
option is also used,
.B grep
stops after outputting
.I NUM
non-matching lines.
.TP
.BR \-o ", " \-\^\-only\-matching
Print only the matched (non-empty) parts of a matching line,
with each such part on a separate output line.
.TP
.BR \-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
.B \-s
or
.B \-\^\-no\-messages
option.
.TP
.BR \-s ", " \-\^\-no\-messages
Suppress error messages about nonexistent or unreadable files.
.SS "Output Line Prefix Control"
.TP
.BR \-b ", " \-\^\-byte\-offset
Print the 0-based byte offset within the input file
before each line of output.
If
.B \-o
.RB ( \-\^\-only\-matching )
is specified,
print the offset of the matching part itself.
.TP
.BR \-H ", " \-\^\-with\-filename
Print the file name for each match.
This is the default when there is more than one file to search.
.TP
.BR \-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.
.TP
.BI \-\^\-label= LABEL
Display input actually coming from standard input as input coming from file
.IR LABEL .
This is especially useful when implementing tools like
.BR zgrep ,
e.g.,
.BR "gzip -cd foo.gz | grep --label=foo -H something" .
See also the
.B \-H
option.
.TP
.BR \-n ", " \-\^\-line\-number
Prefix each line of output with the 1-based line number
within its input file.
.TP
.BR \-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:
.BR \-H , \-n ,
and
.BR \-b .
In order to improve the probability that lines
from a single file will all start at the same column,
this also causes the line number and byte offset (if present)
to be printed in a minimum size field width.
.TP
.BR \-u ", " \-\^\-unix\-byte\-offsets
Report Unix-style byte offsets.
This switch causes
.B grep
to report byte offsets as if the file were a Unix-style text file,
i.e., with CR characters stripped off.
This will produce results identical to running
.B grep
on a Unix machine.
This option has no effect unless
.B \-b
option is also used;
it has no effect on platforms other than MS-DOS and MS-Windows.
.TP
.BR \-Z ", " \-\^\-null
Output a zero byte (the ASCII
.B NUL
character) instead of the character that normally follows a file name.
For example,
.B "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
.BR "find \-print0" ,
.BR "perl \-0" ,
.BR "sort \-z" ,
and
.B "xargs \-0"
to process arbitrary file names,
even those that contain newline characters.
.SS "Context Line Control"
.TP
.BI \-A " NUM" "\fR,\fP \-\^\-after\-context=" NUM
Print
.I NUM
lines of trailing context after matching lines.
Places a line containing a group separator
.RB ( \-\^\- )
between contiguous groups of matches.
With the
.B \-o
or
.B \-\^\-only\-matching
option, this has no effect and a warning is given.
.TP
.BI \-B " NUM" "\fR,\fP \-\^\-before\-context=" NUM
Print
.I NUM
lines of leading context before matching lines.
Places a line containing a group separator
.RB ( \-\^\- )
between contiguous groups of matches.
With the
.B \-o
or
.B \-\^\-only\-matching
option, this has no effect and a warning is given.
.TP
.BI \-C " NUM" "\fR,\fP \-" NUM "\fR,\fP \-\^\-context=" NUM
Print
.I NUM
lines of output context.
Places a line containing a group separator
.RB ( \-\^\- )
between contiguous groups of matches.
With the
.B \-o
or
.B \-\^\-only\-matching
option, this has no effect and a warning is given.
.SS "File and Directory Selection"
.TP
.BR \-a ", " \-\^\-text
Process a binary file as if it were text; this is equivalent to the
.B \-\^\-binary\-files=text
option.
.TP
.BI \-\^\-binary\-files= TYPE
If a file's data or metadata
indicate that the file contains binary data,
assume that the file is of type
.IR TYPE .
Non-text bytes indicate binary data; these are either output bytes that are
improperly encoded for the current locale, or null input bytes when the
.B \-z
option is not given.
.IP
By default,
.I TYPE
is
.BR binary ,
and when
.B grep
discovers that a file is binary it suppresses any further output, and
instead outputs either a one-line message saying that a binary file
matches, or no message if there is no match.
.IP
If
.I TYPE
is
.BR without-match ,
when
.B grep
discovers that a file is binary it assumes that the rest of the file
does not match; this is equivalent to the
.B \-I
option.
.IP
If
.I TYPE
is
.BR text ,
.B grep
processes a binary file as if it were text; this is equivalent to the
.B \-a
option.
.IP
When
.I type
is
.BR binary ,
.B grep
may treat non-text bytes as line terminators even without the
.B \-z
option.  This means choosing
.B binary
versus
.B text
can affect whether a pattern matches a file.  For
example, when
.I type
is
.B binary
the pattern
.B q$ might
match
.B q
immediately followed by a null byte, even though this
is not matched when
.I type
is
.BR text .
Conversely, when
.I type
is
.B binary
the pattern
.B .\&
(period) might not match a null byte.
.IP
.I Warning:
The
.B \-a
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
.B \-a
or to set
.B LC_ALL='C'
in the environment, in order to find more matches even if the matches
are unsafe for direct display.
.TP
.BI \-D " ACTION" "\fR,\fP \-\^\-devices=" ACTION
If an input file is a device, FIFO or socket, use
.I ACTION
to process it.
By default,
.I ACTION
is
.BR read ,
which means that devices are read just as if they were ordinary files.
If
.I ACTION
is
.BR skip ,
devices are silently skipped.
.TP
.BI \-d " ACTION" "\fR,\fP \-\^\-directories=" ACTION
If an input file is a directory, use
.I ACTION
to process it.
By default,
.I ACTION
is
.BR read ,
i.e., read directories just as if they were ordinary files.
If
.I ACTION
is
.BR skip ,
silently skip directories.
If
.I ACTION
is
.BR recurse ,
read all files under each directory, recursively,
following symbolic links only if they are on the command line.
This is equivalent to the
.B \-r
option.
.TP
.BI \-\^\-exclude= GLOB
Skip any command-line file with a name suffix that matches the pattern
.IR GLOB ,
using wildcard matching; a name suffix is either the whole
name, or any suffix starting after a
.B /
and before a +non-\fB/\fP.
When searching recursively, skip any subfile whose base name matches
.IR GLOB ;
the base name is the part after the last
.BR / .
A pattern can use
.BR * ,
.BR ? ,
and
.BR [ ... ]
as wildcards, and
.B \e
to quote a wildcard or backslash character literally.
.TP
.BI \-\^\-exclude-from= FILE
Skip files whose base name matches any of the file-name globs read from
.I FILE
(using wildcard matching as described under
.BR \-\^\-exclude ).
.TP
.BI \-\^\-exclude-dir= GLOB
Skip any command-line directory with a name suffix that matches the
pattern
.IR GLOB .
When searching recursively, skip any subdirectory
whose base name matches
.IR GLOB .
Ignore any redundant trailing slashes in
.IR GLOB .
.TP
.BR \-I
Process a binary file as if it did not contain matching data; this is
equivalent to the
.B \-\^\-binary\-files=without-match
option.
.TP
.BI \-\^\-include= GLOB
Search only files whose base name matches
.I GLOB
(using wildcard matching as described under
.BR \-\^\-exclude ).
.TP
.BR \-r ", " \-\^\-recursive
Read all files under each directory, recursively,
following symbolic links only if they are on the command line.
Note that if no file operand is given, grep searches the working directory.
This is equivalent to the
.B "\-d recurse"
option.
.TP
.BR \-R ", " \-\^\-dereference\-recursive
Read all files under each directory, recursively.
Follow all symbolic links, unlike
.BR \-r .
.SS "Other Options"
.TP
.BR \-\^\-line\-buffered
Use line buffering on output.
This can cause a performance penalty.
.TP
.BR \-U ", " \-\^\-binary
Treat the file(s) as binary.
By default, under MS-DOS and MS-Windows,
.BR grep
guesses whether a file is text or binary as described for the
.B \-\^\-binary\-files
option.
If
.BR grep
decides the file is a text file, it strips the CR characters from the
original file contents (to make regular expressions with
.B ^
and
.B $
work correctly).
Specifying
.B \-U
overrules this guesswork, causing all files to be read and passed to the
matching mechanism verbatim; if the file is a text file with CR/LF
pairs at the end of each line, this will cause some regular
expressions to fail.
This option has no effect on platforms
other than MS-DOS and MS-Windows.
.TP
.BR \-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
.B \-Z
or
.B \-\^\-null
option, this option can be used with commands like
.B sort -z
to process arbitrary file names.
.
.SH "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.
.PP
.B grep
understands three different versions of regular expression syntax:
\*(lqbasic\*(rq (BRE), \*(lqextended\*(rq (ERE) and \*(lqperl\*(rq (PCRE).
In GNU
.B grep
there is no difference in available functionality between basic and
extended syntaxes.
In other implementations, basic regular expressions are less powerful.
The following description applies to extended regular expressions;
differences for basic regular expressions are summarized afterwards.
Perl-compatible regular expressions give additional functionality, and are
documented in pcresyntax(3) and pcrepattern(3), but work only if
PCRE is available in the system.
.PP
The fundamental building blocks are the regular expressions
that match a single character.
Most characters, including all letters and digits,
are regular expressions that match themselves.
Any meta-character with special meaning
may be quoted by preceding it with a backslash.
.PP
The period
.B .\&
matches any single character.
.SS "Character Classes and Bracket Expressions"
A
.I "bracket expression"
is a list of characters enclosed by
.B [
and
.BR ] .
It matches any single
character in that list; if the first character of the list
is the caret
.B ^
then it matches any character
.I not
in the list.
For example, the regular expression
.B [0123456789]
matches any single digit.
.PP
Within a bracket expression, a
.I "range expression"
consists of two characters separated by a hyphen.
It matches any single character that sorts between the two characters,
inclusive, using the locale's collating sequence and character set.
For example, in the default C locale,
.B [a\-d]
is equivalent to
.BR [abcd] .
Many locales sort characters in dictionary order, and in these locales
.B [a\-d]
is typically not equivalent to
.BR [abcd] ;
it might be equivalent to
.BR [aBbCcDd] ,
for example.
To obtain the traditional interpretation of bracket expressions,
you can use the C locale by setting the
.B LC_ALL
environment variable to the value
.BR C .
.PP
Finally, certain named classes of characters are predefined within
bracket expressions, as follows.
Their names are self explanatory, and they are
.BR [:alnum:] ,
.BR [:alpha:] ,
.BR [:cntrl:] ,
.BR [:digit:] ,
.BR [:graph:] ,
.BR [:lower:] ,
.BR [:print:] ,
.BR [:punct:] ,
.BR [:space:] ,
.BR [:upper:] ,
and
.BR [:xdigit:].
For example,
.B [[:alnum:]]
means the character class of numbers and
letters in the current locale.
In the C locale and ASCII
character set encoding, this is the same as
.BR [0\-9A\-Za\-z] .
(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.)
Most meta-characters lose their special meaning inside bracket expressions.
To include a literal
.B ]
place it first in the list.
Similarly, to include a literal
.B ^
place it anywhere but first.
Finally, to include a literal
.B \-
place it last.
.SS Anchoring
The caret
.B ^
and the dollar sign
.B $
are meta-characters that respectively match the empty string at the
beginning and end of a line.
.SS "The Backslash Character and Special Expressions"
The symbols
.B \e<
and
.B \e>
respectively match the empty string at the beginning and end of a word.
The symbol
.B \eb
matches the empty string at the edge of a word,
and
.B \eB
matches the empty string provided it's
.I not
at the edge of a word.
The symbol
.B \ew
is a synonym for
.B [_[:alnum:]]
and
.B \eW
is a synonym for
.BR [^_[:alnum:]] .
.SS Repetition
A regular expression may be followed by one of several repetition operators:
.PD 0
.TP
.B ?
The preceding item is optional and matched at most once.
.TP
.B *
The preceding item will be matched zero or more times.
.TP
.B +
The preceding item will be matched one or more times.
.TP
.BI { n }
The preceding item is matched exactly
.I n
times.
.TP
.BI { n ,}
The preceding item is matched
.I n
or more times.
.TP
.BI {, m }
The preceding item is matched at most
.I m
times.
This is a GNU extension.
.TP
.BI { n , m }
The preceding item is matched at least
.I n
times, but not more than
.I m
times.
.PD
.SS Concatenation
Two regular expressions may be concatenated; the resulting
regular expression matches any string formed by concatenating
two substrings that respectively match the concatenated
expressions.
.SS Alternation
Two regular expressions may be joined by the infix operator
.BR | ;
the resulting regular expression matches any string matching
either alternate expression.
.SS Precedence
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.
.SS "Back References and Subexpressions"
The back-reference
.BI \e n\c
\&, where
.I n
is a single digit, matches the substring
previously matched by the
.IR n th
parenthesized subexpression of the regular expression.
.SS "Basic vs Extended Regular Expressions"
In basic regular expressions the meta-characters
.BR ? ,
.BR + ,
.BR { ,
.BR | ,
.BR ( ,
and
.BR )
lose their special meaning; instead use the backslashed
versions
.BR \e? ,
.BR \e+ ,
.BR \e{ ,
.BR \e| ,
.BR \e( ,
and
.BR \e) .
.
.SH "ENVIRONMENT VARIABLES"
The behavior of
.B grep
is affected by the following environment variables.
.PP
The locale for category
.BI LC_ foo
is specified by examining the three environment variables
.BR LC_ALL ,
.BR LC_\fIfoo\fP ,
.BR LANG ,
in that order.
The first of these variables that is set specifies the locale.
For example, if
.B LC_ALL
is not set, but
.B LC_MESSAGES
is set to
.BR pt_BR ,
then the Brazilian Portuguese locale is used for the
.B 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
.B grep
was not compiled with national language support (NLS).
The shell command
.B "locale \-a"
lists locales that are currently available.
.TP
.B GREP_OPTIONS
This variable specifies default options
to be placed in front of any explicit options.
As this causes problems when writing portable scripts,
this feature will be removed in a future release of
.BR grep ,
and
.B grep
warns if it is used.
Please use an alias or script instead.
.TP
.B GREP_COLOR
This variable specifies the color used to highlight matched (non-empty) text.
It is deprecated in favor of
.BR GREP_COLORS ,
but still supported.
The
.BR mt ,
.BR ms ,
and
.B mc
capabilities of
.B GREP_COLORS
have priority over it.
It can only specify the color used to highlight
the matching non-empty text in any matching line
(a selected line when the
.B -v
command-line option is omitted,
or a context line when
.B -v
is specified).
The default is
.BR 01;31 ,
which means a bold red foreground text on the terminal's default background.
.TP
.B GREP_COLORS
Specifies the colors and other attributes
used to highlight various parts of the output.
Its value is a colon-separated list of capabilities
that defaults to
.B ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36
with the
.B rv
and
.B ne
boolean capabilities omitted (i.e., false).
Supported capabilities are as follows.
.RS
.TP
.B sl=
SGR substring for whole selected lines
(i.e.,
matching lines when the
.B \-v
command-line option is omitted,
or non-matching lines when
.B \-v
is specified).
If however the boolean
.B rv
capability
and the
.B \-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).
.TP
.B cx=
SGR substring for whole context lines
(i.e.,
non-matching lines when the
.B \-v
command-line option is omitted,
or matching lines when
.B \-v
is specified).
If however the boolean
.B rv
capability
and the
.B \-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).
.TP
.B rv
Boolean value that reverses (swaps) the meanings of
the
.B sl=
and
.B cx=
capabilities
when the
.B \-v
command-line option is specified.
The default is false (i.e., the capability is omitted).
.TP
.B mt=01;31
SGR substring for matching non-empty text in any matching line
(i.e.,
a selected line when the
.B \-v
command-line option is omitted,
or a context line when
.B \-v
is specified).
Setting this is equivalent to setting both
.B ms=
and
.B mc=
at once to the same value.
The default is a bold red text foreground over the current line background.
.TP
.B ms=01;31
SGR substring for matching non-empty text in a selected line.
(This is only used when the
.B \-v
command-line option is omitted.)
The effect of the
.B sl=
(or
.B cx=
if
.BR rv )
capability remains active when this kicks in.
The default is a bold red text foreground over the current line background.
.TP
.B mc=01;31
SGR substring for matching non-empty text in a context line.
(This is only used when the
.B \-v
command-line option is specified.)
The effect of the
.B cx=
(or
.B sl=
if
.BR rv )
capability remains active when this kicks in.
The default is a bold red text foreground over the current line background.
.TP
.B fn=35
SGR substring for file names prefixing any content line.
The default is a magenta text foreground over the terminal's default background.
.TP
.B ln=32
SGR substring for line numbers prefixing any content line.
The default is a green text foreground over the terminal's default background.
.TP
.B bn=32
SGR substring for byte offsets prefixing any content line.
The default is a green text foreground over the terminal's default background.
.TP
.B se=36
SGR substring for separators that are inserted
between selected line fields
.RB ( : ),
between context line fields,
.RB ( \- ),
and between groups of adjacent lines when nonzero context is specified
.RB ( \-\^\- ).
The default is a cyan text foreground over the terminal's default background.
.TP
.B ne
Boolean value that prevents clearing to the end of line
using Erase in Line (EL) to Right
.RB ( \\\\\\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
.B back_color_erase
.RB ( 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).
.PP
Note that boolean capabilities have no
.BR = ...
part.
They are omitted (i.e., false) by default and become true when specified.
.PP
See the Select Graphic Rendition (SGR) section
in the documentation of the text terminal that is used
for permitted values and their meaning as character attributes.
These substring values are integers in decimal representation
and can be concatenated with semicolons.
.B grep
takes care of assembling the result
into a complete SGR sequence
.RB ( \\\\\\33[ ... m ).
Common values to concatenate include
.B 1
for bold,
.B 4
for underline,
.B 5
for blink,
.B 7
for inverse,
.B 39
for default foreground color,
.B 30
to
.B 37
for foreground colors,
.B 90
to
.B 97
for 16-color mode foreground colors,
.B 38;5;0
to
.B 38;5;255
for 88-color and 256-color modes foreground colors,
.B 49
for default background color,
.B 40
to
.B 47
for background colors,
.B 100
to
.B 107
for 16-color mode background colors, and
.B 48;5;0
to
.B 48;5;255
for 88-color and 256-color modes background colors.
.RE
.TP
\fBLC_ALL\fP, \fBLC_COLLATE\fP, \fBLANG\fP
These variables specify the locale for the
.B LC_COLLATE
category,
which determines the collating sequence
used to interpret range expressions like
.BR [a\-z] .
.TP
\fBLC_ALL\fP, \fBLC_CTYPE\fP, \fBLANG\fP
These variables specify the locale for the
.B LC_CTYPE
category,
which determines the type of characters,
e.g., which characters are whitespace.
This category also determines the character encoding, that is, whether
text is encoded in UTF-8, ASCII, or some other encoding.  In the C or
POSIX locale, all characters are encoded as a single byte and every
byte is a valid character.
.TP
\fBLC_ALL\fP, \fBLC_MESSAGES\fP, \fBLANG\fP
These variables specify the locale for the
.B LC_MESSAGES
category,
which determines the language that
.B grep
uses for messages.
The default C locale uses American English messages.
.TP
.B POSIXLY_CORRECT
If set,
.B grep
behaves as POSIX requires; otherwise,
.B grep
behaves more like other GNU programs.
POSIX requires that options that follow file names must be
treated as file names; by default, such options are permuted to the
front of the operand list and are treated as options.
Also, POSIX requires that unrecognized options be diagnosed as
\*(lqillegal\*(rq, but since they are not really against the law the default
is to diagnose them as \*(lqinvalid\*(rq.
.B POSIXLY_CORRECT
also disables \fB_\fP\fIN\fP\fB_GNU_nonoption_argv_flags_\fP,
described below.
.TP
\fB_\fP\fIN\fP\fB_GNU_nonoption_argv_flags_\fP
(Here
.I N
is
.BR grep 's
numeric process ID.)  If the
.IR i th
character of this environment variable's value is
.BR 1 ,
do not consider the
.IR i th
operand of
.B grep
to be an option, even if it appears to be one.
A shell can put this variable in the environment for each command it runs,
specifying which operands are the results of file name wildcard
expansion and therefore should not be treated as options.
This behavior is available only with the GNU C library, and only
when
.B POSIXLY_CORRECT
is not set.
.
.SH "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
.B \-q
or
.B \-\^\-quiet
or
.B \-\^\-silent
is used and a line is selected, the exit status is 0 even if an error
occurred.
.
.SH COPYRIGHT
Copyright 1998\(en2000, 2002, 2005\(en2017 Free Software Foundation, Inc.
.PP
This is free software;
see the source for copying conditions.
There is NO warranty;
not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
.
.SH BUGS
.SS "Reporting Bugs"
Email bug reports to
.MTO bug-grep@gnu.org "the bug-reporting address" .
An
.URL http://lists.gnu.org/mailman/listinfo/bug-grep "email archive"
and a
.URL http://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep "bug tracker"
are available.
.SS "Known Bugs"
Large repetition counts in the
.BI { n , m }
construct may cause
.B grep
to use lots of memory.
In addition,
certain other obscure regular expressions require exponential time
and space, and may cause
.B grep
to run out of memory.
.PP
Back-references are very slow, and may require exponential time.
.
.SH "SEE ALSO"
.SS "Regular Manual Pages"
awk(1), cmp(1), diff(1), find(1), gzip(1),
perl(1), sed(1), sort(1), xargs(1), zgrep(1),
read(2),
pcre(3), pcresyntax(3), pcrepattern(3),
terminfo(5),
glob(7), regex(7).
.SS "POSIX Programmer's Manual Page"
grep(1p).
.SS "Full Documentation"
A
.URL http://www.gnu.org/software/grep/manual/ "complete manual"
is available.
If the
.B info
and
.B grep
programs are properly installed at your site, the command
.IP
.B info grep
.PP
should give you access to the complete manual.
.
.SH NOTES
This man page is maintained only fitfully;
the full documentation is often more up-to-date.
.\" Work around problems with some troff -man implementations.
.br