GREP(1) User Commands GREP(1)
NAME
grep, egrep, fgrep, rgrep - print lines that match patterns
SYNOPSIS
grep [OPTION...] PATTERNS [FILE...]
grep [OPTION...] -e PATTERNS ... [FILE...]
grep [OPTION...] -f PATTERN_FILE ... [FILE...]
DESCRIPTION
grep searches for PATTERNS in each FILE. PATTERNS is one or more
patterns separated by newline characters, and grep prints each line
that matches a pattern. Typically PATTERNS should be quoted when grep
is used in a shell command.
A FILE of "-" stands for standard input. If no FILE is given,
recursive searches examine the working directory, and nonrecursive
searches read standard input.
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.
Pattern Syntax
-E, --extended-regexp
Interpret PATTERNS as extended regular expressions (EREs, see
below).
-F, --fixed-strings
Interpret PATTERNS as fixed strings, not regular expressions.
-G, --basic-regexp
Interpret PATTERNS as basic regular expressions (BREs, see
below). This is the default.
-P, --perl-regexp
Interpret PATTERNS as Perl-compatible regular expressions
(PCREs). This option is experimental when combined with the -z
(--null-data) option, and grep -P may warn of unimplemented
features.
Matching Control
-e PATTERNS, --regexp=PATTERNS
Use PATTERNS as the patterns. 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 patterns and input data, so that
characters that differ only in case match each other.
--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, to cancel its effects because the
two options override each other.
-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. This option has no effect if -x is also specified.
-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 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'. 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 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, or null input
bytes when the -z option is not given.
By default, TYPE is binary, and grep suppresses output after
null input binary data is discovered, and suppresses output
lines that contain improperly encoded data. When some output is
suppressed, grep follows any output with a one-line message
saying that a binary file matches.
If TYPE is without-match, when grep discovers null input binary
data it assumes that the rest of the file does not match; this
is equivalent to the -I option.
If TYPE is text, grep processes a binary file 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 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 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. 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 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 base name matches any of the file-name globs
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 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 whether a file is text or binary as
described for the --binary-files option. 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 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.
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. It is unspecified whether
it matches an encoding error.
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;
it is unspecified whether it matches an encoding error. 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:], [:blank:], [: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 \?,
\+, \{, \|, \(, and \).
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.
ENVIRONMENT
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). The shell command locale -a lists locales that
are currently available.
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. 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.
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.
NOTES
This man page is maintained only fitfully; the full documentation is
often more up-to-date.
COPYRIGHT
Copyright 1998-2000, 2002, 2005-2020 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 <https://lists.gnu.org/mailman/listinfo/bug-grep> and a
bug tracker <https://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.
EXAMPLE
The following example outputs the location and contents of any line
containing "f" and ending in ".c", within all files in the current di-
rectory whose names contain "g" and end in ".h". The -n option outputs
line numbers, the -- argument treats expansions of "*g*.h" starting
with "-" as file names not options, and the empty file /dev/null causes
file names to be output even if only one file name happens to be of the
form "*g*.h".
$ grep -n -- 'f.*\.c$' *g*.h /dev/null
argmatch.h:1:/* definitions and prototypes for argmatch.c
The only line that matches is line 1 of argmatch.h. Note that the reg-
ular expression syntax used in the pattern differs from the globbing
syntax that the shell uses to match file names.
SEE ALSO
Regular Manual Pages
awk(1), cmp(1), diff(1), find(1), perl(1), sed(1), sort(1), xargs(1),
read(2), pcre(3), pcresyntax(3), pcrepattern(3), terminfo(5), glob(7),
regex(7).
Full Documentation
A complete manual <https://www.gnu.org/software/grep/manual/> is avail-
able. If the info and grep programs are properly installed at your
site, the command
info grep
should give you access to the complete manual.
GNU grep 3.4 2019-12-29 GREP(1)