Provided by: grep_2.25-1~16.04.1_amd64 
NAME
grep, egrep, fgrep, rgrep - print lines matching a pattern
SYNOPSIS
grep [OPTIONS] PATTERN [FILE...]
grep [OPTIONS] [-e PATTERN]... [-f FILE]... [FILE...]
DESCRIPTION
grep searches the named input FILEs for lines containing a match to the given PATTERN. If no files are
specified, or if the file “-” is given, grep searches standard input. By default, grep prints the
matching lines.
In addition, the variant programs egrep, fgrep and rgrep are the same as grep -E, grep -F, and grep -r,
respectively. These variants are deprecated, but are provided for backward compatibility.
OPTIONS
Generic Program Information
--help Output a usage message and exit.
-V, --version
Output the version number of grep and exit.
Matcher Selection
-E, --extended-regexp
Interpret PATTERN as an extended regular expression (ERE, see below).
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings (instead of regular expressions), separated by
newlines, any of which is to be matched.
-G, --basic-regexp
Interpret PATTERN as a basic regular expression (BRE, see below). This is the default.
-P, --perl-regexp
Interpret the pattern as a Perl-compatible regular expression (PCRE). This is highly experimental
and grep -P may warn of unimplemented features.
Matching Control
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern. If this option is used multiple times or is combined with the -f
(--file) option, search for all patterns given. This option can be used to protect a pattern
beginning with “-”.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. If this option is used multiple times or is combined
with the -e (--regexp) option, search for all patterns given. The empty file contains zero
patterns, and therefore matches nothing.
-i, --ignore-case
Ignore case distinctions in both the PATTERN and the input files.
-v, --invert-match
Invert the sense of matching, to select non-matching lines.
-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.
-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 ^ and $.
-y Obsolete synonym for -i.
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 (see below), count non-matching lines.
--color[=WHEN], --colour[=WHEN]
Surround the matched (non-empty) strings, matching lines, context lines, file names, line numbers,
byte offsets, and separators (for fields and groups of context lines) with escape sequences to
display them in color on the terminal. The colors are defined by the environment variable
GREP_COLORS. The deprecated environment variable GREP_COLOR is still supported, but its setting
does not have priority. WHEN is never, always, or auto.
-L, --files-without-match
Suppress normal output; instead print the name of each input file from which no output would
normally have been printed. The scanning will stop on the first match.
-l, --files-with-matches
Suppress normal output; instead print the name of each input file from which output would normally
have been printed. The scanning will stop on the first match.
-m NUM, --max-count=NUM
Stop reading a file after NUM matching lines. If the input is standard input from a regular file,
and NUM matching lines are output, grep ensures that the standard input is positioned to just
after the last matching line before exiting, regardless of the presence of trailing context lines.
This enables a calling process to resume a search. When grep stops after NUM matching 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 a matching line, with each such part on a separate
output line.
-q, --quiet, --silent
Quiet; do not write anything to standard output. Exit immediately with zero status if any match
is found, even if an error was detected. Also see the -s or --no-messages option.
-s, --no-messages
Suppress error messages about nonexistent or unreadable files.
Output Line Prefix Control
-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 is
especially useful when implementing tools like zgrep, e.g., gzip -cd foo.gz | grep --label=foo -H
something. See also the -H option.
-n, --line-number
Prefix each line of output with the 1-based line number within its input file.
-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. 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.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes 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 grep on a Unix machine. This option has no effect unless -b option is also
used; it has no effect on platforms other than MS-DOS and MS-Windows.
-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.
Context Line Control
-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching lines. Places a line containing a group
separator (--) between contiguous groups of matches. With the -o or --only-matching option, this
has no effect and a warning is given.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching lines. Places a line containing a group
separator (--) between contiguous groups of matches. With the -o or --only-matching option, this
has no effect and a warning is given.
-C NUM, -NUM, --context=NUM
Print NUM lines of output context. Places a line containing a group separator (--) between
contiguous groups of matches. With the -o or --only-matching option, this has no effect and a
warning is given.
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 the first few bytes of a file indicate that the file contains binary data, assume that the file
is of type TYPE. By default, TYPE is binary, and grep normally outputs either a one-line message
saying that a binary file matches, or no message if there is no match. If TYPE is without-match,
grep assumes that a binary file does not match; this is equivalent to the -I option. If TYPE is
text, grep processes a binary file as if it were text; this is equivalent to the -a option. When
processing binary data, grep may treat non-text bytes as line terminators; for example, the
pattern '.' (period) might not match a null byte, as the null byte might be treated as a line
terminator. Warning: grep --binary-files=text might output binary garbage, which can have nasty
side effects if the output is a terminal and if the terminal driver interprets some of it as
commands.
-D ACTION, --devices=ACTION
If an input file is a device, FIFO or socket, use ACTION to process it. By default, ACTION is
read, which means that devices are read just as if they were ordinary files. If ACTION is skip,
devices are silently skipped.
-d ACTION, --directories=ACTION
If an input file is a directory, use ACTION to process it. By default, ACTION is read, i.e., read
directories just as if they were ordinary files. If ACTION is skip, silently skip directories.
If ACTION is recurse, read all files under each directory, recursively, following symbolic links
only if they are on the command line. This is equivalent to the -r option.
--exclude=GLOB
Skip files whose base name matches GLOB (using wildcard matching). A file-name glob can use *, ?,
and [...] as wildcards, and \ to quote a wildcard or backslash character literally.
--exclude-from=FILE
Skip files whose base name matches any of the file-name globs read from FILE (using wildcard
matching as described under --exclude).
--exclude-dir=DIR
Exclude directories matching the pattern DIR from recursive searches.
-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 base name matches GLOB (using wildcard matching as described under
--exclude).
-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 -d recurse option.
-R, --dereference-recursive
Read all files under each directory, recursively. Follow all symbolic links, unlike -r.
Other Options
--line-buffered
Use line buffering on output. This can cause a performance penalty.
-U, --binary
Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep guesses the file type
by looking at the contents of the first 32KB read from the file. If grep decides the file is a
text file, it strips the CR characters from the original file contents (to make regular
expressions with ^ and $ work correctly). Specifying -U overrules this guesswork, causing all
files to be read and passed to the matching mechanism verbatim; if the file is a text file with
CR/LF pairs at the end of each line, this will cause some regular expressions to fail. This
option has no effect on platforms other than MS-DOS and MS-Windows.
-z, --null-data
Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character)
instead of a newline. Like the -Z or --null option, this option can be used with commands like
sort -z to process arbitrary file names.
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” (PCRE). In GNU 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.
The fundamental building blocks are the regular expressions that match a single character. Most
characters, including all letters and digits, are regular expressions that match themselves. Any meta-
character with special meaning may be quoted by preceding it with a backslash.
The period . matches any single character.
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. For example, the regular expression [0123456789] matches any single digit.
Within a bracket expression, a range expression consists of two characters separated by a hyphen. It
matches any single character that sorts between the two characters, inclusive, using the locale's
collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to
[abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not
equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example. To obtain the traditional
interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environment
variable to the value C.
Finally, certain named classes of characters are predefined within bracket expressions, as follows.
Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:],
[:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[: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 [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 ] place
it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to
include a literal - place it last.
Anchoring
The caret ^ and the dollar sign $ are meta-characters that respectively match the empty string at the
beginning and end of a line.
The Backslash Character and Special Expressions
The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol
\b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at
the edge of a word. The symbol \w is a synonym for [_[:alnum:]] and \W is a synonym for [^_[:alnum:]].
Repetition
A regular expression may be followed by one of several repetition operators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{,m} The preceding item is matched at most m times. This is a GNU extension.
{n,m} The preceding item is matched at least n times, but not more than m times.
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.
Alternation
Two regular expressions may be joined by the infix operator |; the resulting regular expression matches
any string matching either alternate expression.
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.
Back References and Subexpressions
The back-reference \n, where n is a single digit, matches the substring previously matched by the nth
parenthesized subexpression of the regular expression.
Basic vs Extended Regular Expressions
In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead
use the backslashed versions \?, \+, \{, \|, \(, and \).
ENVIRONMENT VARIABLES
The behavior of grep is affected by the following environment variables.
The locale for category LC_foo is specified by examining the three environment variables LC_ALL, LC_foo,
LANG, in that order. The first of these variables that is set specifies the locale. For example, if
LC_ALL is not set, but LC_MESSAGES is set to pt_BR, then the Brazilian Portuguese locale is used for 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).
GREP_OPTIONS
This variable specifies default options to be placed in front of any explicit options. As this
causes problems when writing portable scripts, this feature will be removed in a future release of
grep, and grep warns if it is used. Please use an alias or script instead.
GREP_COLOR
This variable specifies the color used to highlight matched (non-empty) text. It is deprecated in
favor of GREP_COLORS, but still supported. The mt, ms, and mc capabilities of GREP_COLORS have
priority over it. It can only specify the color used to highlight the matching non-empty text in
any matching line (a selected line when the -v command-line option is omitted, or a context line
when -v is specified). The default is 01;31, which means a bold red foreground text on the
terminal's default background.
GREP_COLORS
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
ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36 with the rv and ne boolean capabilities omitted
(i.e., false). Supported capabilities are as follows.
sl= SGR substring for whole selected lines (i.e., matching lines when the -v command-line
option is omitted, or non-matching lines when -v is specified). If however the boolean rv
capability and the -v command-line option are both specified, it applies to context
matching lines instead. The default is empty (i.e., the terminal's default color pair).
cx= SGR substring for whole context lines (i.e., non-matching lines when the -v command-line
option is omitted, or matching lines when -v is specified). If however the boolean rv
capability and the -v command-line option are both specified, it applies to selected non-
matching lines instead. The default is empty (i.e., the terminal's default color pair).
rv Boolean value that reverses (swaps) the meanings of the sl= and cx= capabilities when the
-v command-line option is specified. The default is false (i.e., the capability is
omitted).
mt=01;31
SGR substring for matching non-empty text in any matching line (i.e., a selected line when
the -v command-line option is omitted, or a context line when -v is specified). Setting
this is equivalent to setting both ms= and mc= at once to the same value. The default is a
bold red text foreground over the current line background.
ms=01;31
SGR substring for matching non-empty text in a selected line. (This is only used when the
-v command-line option is omitted.) The effect of the sl= (or cx= if rv) capability
remains active when this kicks in. 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 only used when the
-v command-line option is specified.) The effect of the cx= (or sl= if rv) capability
remains active when this kicks in. 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.
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. 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.
LC_ALL, LC_COLLATE, LANG
These variables specify the locale for the LC_COLLATE category, which determines the collating
sequence used to interpret range expressions like [a-z].
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.
LC_ALL, LC_MESSAGES, LANG
These variables specify the locale for the LC_MESSAGES category, which determines the language
that grep uses for messages. The default C locale uses American English messages.
POSIXLY_CORRECT
If set, grep behaves as POSIX requires; otherwise, grep behaves more like other GNU programs.
POSIX requires that options that follow file names must be treated as file names; by default, such
options are permuted to the front of the operand list and are treated as options. Also, POSIX
requires that unrecognized options be diagnosed as “illegal”, but since they are not really
against the law the default is to diagnose them as “invalid”. POSIXLY_CORRECT also disables
_N_GNU_nonoption_argv_flags_, described below.
_N_GNU_nonoption_argv_flags_
(Here N is grep's numeric process ID.) If the ith character of this environment variable's value
is 1, do not consider the ith operand of grep to be an option, even if it appears to be one. A
shell can put this variable in the environment for each command it runs, specifying which operands
are the results of file name wildcard expansion and therefore should not be treated as options.
This behavior is available only with the GNU C library, and only when POSIXLY_CORRECT is not set.
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 is used and a line is selected, the exit status is 0
even if an error occurred.
COPYRIGHT
Copyright 1998-2000, 2002, 2005-2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
BUGS
Reporting Bugs
Email bug reports to the bug-reporting address ⟨bug-grep@gnu.org⟩. An email archive ⟨http://
lists.gnu.org/mailman/listinfo/bug-grep⟩ and a bug tracker ⟨http://debbugs.gnu.org/cgi/
pkgreport.cgi?package=grep⟩ are available.
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 are very slow, and may require exponential time.
SEE ALSO
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).
POSIX Programmer's Manual Page
grep(1p).
Full Documentation
A complete manual ⟨http://www.gnu.org/software/grep/manual/⟩ is available. If the info and grep programs
are properly installed at your site, the command
info grep
should give you access to the complete manual.
NOTES
This man page is maintained only fitfully; the full documentation is often more up-to-date.