User Commands GREP(1)
NAME
grep, egrep, fgrep - print lines matching a pattern
SYNOPSIS
grep [options] PATERN [FILE...]
grep [options] [-e PATERN -f FILE] [FILE...]
DESCRIPTION
Grep searches the named input FILEs (or standard input if no
files are named, or the file name - is given) for lines con-
taining a match to the given PATERN. By default, grep
prints the matching lines.
In addition, two variant programs egrep and fgrep are avail-
able. Egrep is the same as grep -E. Fgrep is the same as
grep -F.
OPTIONS
-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching
lines. Places a line containing -- between contiguous
groups of matches.
-a, --text
Process a binary file as if it were text; this is
equivalent to the --binary-files=text option.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching
lines. Places a line containing -- between contiguous
groups of matches.
-C NUM, --context=NUM
Print NUM lines of output context. Places a line con-
taining -- between contiguous groups of matches.
-b, --byte-offset
Print the byte offset within the input file before each
line of output.
--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. Warn-
ing: grep --binary-files=text might output binary gar-
bage, which can have nasty side effects if the output
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is a terminal and if the terminal driver interprets
some of it as commands.
--colour[=WHEN], --color[=WHEN]
Surround the matching string with the marker find in
GREPCOLOR environment variable. WHEN may be `never',
`always', or `auto'
-c, --count
Suppress normal output; instead print a count of match-
ing lines for each input file. With the -v, --invert-
match option (see below), count non-matching lines.
-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, which means that
directories are read just as if they were ordinary
files. If ACTION is skip, directories are silently
skipped. If ACTION is recurse, grep reads all files
under each directory, recursively; this is equivalent
to the -r option.
-E, --extended-regexp
Interpret PATERN as an extended regular expression
(see below).
-e PATERN, --regexp=PATERN
Use PATERN as the pattern; useful to protect patterns
beginning with -.
-F, --fixed-strings
Interpret PATERN as a list of fixed strings, separated
by newlines, any of which is to be matched. -P,
--perl-regexp Interpret PATERN as a Perl regular
expression.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. The empty
file contains zero patterns, and therefore matches
nothing.
-G, --basic-regexp
Interpret PATERN as a basic regular expression (see
below). This is the default.
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-H, --with-filename
Print the filename for each match.
-h, --no-filename
Suppress the prefixing of filenames on output when mul-
tiple files are searched.
--help
Output a brief help message.
-I Process a binary file as if it did not contain matching
data; this is equivalent to the --binary-
files=without-match option.
-i, --ignore-case
Ignore case distinctions in both the PATERN and the
input files.
-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 stan-
dard input is positioned to just after the last match-
ing 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.
--mmap
If possible, use the mmap(2) system call to read input,
instead of the default read(2) system call. In some
situations, --mmap yields better performance. However,
--mmap can cause undefined behavior (including core
dumps) if an input file shrinks while grep is operat-
ing, or if an I/O error occurs.
-n, --line-number
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Prefix each line of output with the line number within
its input file.
-o, --only-matching
Show only the part of a matching line that matches PAT-
TERN.
--label=LABEL
Displays input actually coming from standard input as
input coming from file LABEL. This is especially useful
for tools like zgrep, e.g. gzip -cd foo.gz grep --
label=foo something
--line-buffering
Use line buffering, it can be a performance penality.
-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.
-R, -r, --recursive
Read all files under each directory, recursively; this
is equivalent to the -d recurse option.
--include=PATERN
Recurse in directories only searching file matching
PATERN.
--exclude=PATERN
Recurse in directories skip file matching PATERN.
-s, --no-messages
Suppress error messages about nonexistent or unreadable
files. Portability note: unlike GNU grep, traditional
grep did not conform to POSIX.2, because traditional
grep lacked a -q option and its -s option behaved like
GNU grep's -q option. Shell scripts intended to be
portable to traditional grep should avoid both -q and
-s and should redirect output to /dev/null instead.
-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
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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.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes
grep to report byte offsets as if the file were 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.
-V, --version
Print the version number of grep to standard error.
This version number should be included in all bug
reports (see below).
-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 pre-
ceded 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.
-y Obsolete synonym for -i.
-Z, --null
Output a zero byte (the ASCI 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.
REGULAR EXPRESIONS
A regular expression is a pattern that describes a set of
strings. Regular expressions are constructed analogously to
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arithmetic expressions, by using various operators to com-
bine smaller expressions.
Grep understands two different versions of regular expres-
sion syntax: "basic" and "extended." In GNU grep, there is
no difference in available functionality using either syn-
tax. 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.
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 metacharacter with special meaning may be
quoted by preceding it with a backslash.
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 expres-
sions, you can use the C locale by setting the LCAL
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 exam-
ple, [:alnum:] means [0-9A-Za-z], except the latter form
depends upon the C locale and the ASCI character encoding,
whereas the former is independent of locale and character
set. (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 list.) Most metacharac-
ters lose their special meaning inside lists. 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.
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The period . matches any single character. The symbol \w is
a synonym for [:alnum:] and \W is a synonym for
[^[:alnum].
The caret ^ and the dollar sign $ are metacharacters that
respectively match the empty string at the beginning and end
of a line. 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.
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.
{n,m}
The preceding item is matched at least n times, but not
more than m times.
Two regular expressions may be concatenated; the resulting
regular expression matches any string formed by concatenat-
ing two substrings that respectively match the concatenated
subexpressions.
Two regular expressions may be joined by the infix operator
; the resulting regular expression matches any string
matching either subexpression.
Repetition takes precedence over concatenation, which in
turn takes precedence over alternation. A whole subexpres-
sion may be enclosed in parentheses to override these pre-
cedence rules.
The backreference \n, where n is a single digit, matches the
substring previously matched by the nth parenthesized subex-
pression of the regular expression.
In basic regular expressions the metacharacters ?, ], {, ,
(, and ) lose their special meaning; instead use the
backslashed versions \?, \], \{, \, \(, and \).
Traditional egrep did not support the { metacharacter, and
some egrep implementations support \{ instead, so portable
scripts should avoid { in egrep patterns and should use [{]
to match a literal {.
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GNU egrep attempts to support traditional usage by assuming
that { is not special if it would be the start of an invalid
interval specification. For example, the shell command
egrep '{1' searches for the two-character string {1 instead
of reporting a syntax error in the regular expression.
POSIX.2 allows this behavior as an extension, but portable
scripts should avoid it.
ENVIRONMENT VARIABLES
Grep's behavior is affected by the following environment
variables.
A locale LCfoo is specified by examining the three environ-
ment variables LCAL, LCfoo, LANG, in that order. The
first of these variables that is set specifies the locale.
For example, if LCAL is not set, but LCMESAGES is set to
ptBR, then Brazilian Portuguese is used for the LCMESAGES
locale. The C locale is used if none of these environment
variables are set, or if the locale catalog is not
installed, or if grep was not compiled with national
language support (NLS).
GREPOPTIONS
This variable specifies default options to be placed in
front of any explicit options. For example, if
GREPOPTIONS is '--binary-files=without-match
--directories=skip', grep behaves as if the two options
--binary-files=without-match and --directories=skip had
been specified before any explicit options. Option
specifications are separated by whitespace. A
backslash escapes the next character, so it can be used
to specify an option containing whitespace or a
backslash.
GREPCOLOR
Specifies the marker for highlighting.
LCAL, LCOLATE, LANG
These variables specify the LCOLATE locale, which
determines the collating sequence used to interpret
range expressions like [a-z].
LCAL, LCTYPE, LANG
These variables specify the LCTYPE locale, which
determines the type of characters, e.g., which charac-
ters are whitespace.
LCAL, LCMESAGES, LANG
These variables specify the LCMESAGES locale, which
determines the language that grep uses for messages.
The default C locale uses American English messages.
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POSIXLYCORECT
If set, grep behaves as POSIX.2 requires; otherwise,
grep behaves more like other GNU programs. POSIX.2
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.2 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". POSIXLYCORECT also
disables NGNUnonoptionargvflags, described below.
NGNUnonoptionargvflags
(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 POSIXLYCORECT is not
set.
DIAGNOSTICS
Normally, exit status is 0 if selected lines are found and 1
otherwise. But the exit status is 2 if an error occurred,
unless the -q or --quiet or --silent option is used and a
selected line is found.
BUGS
Email bug reports to bug-gnu-utils@gnu.org. Be sure to
include the word "grep" somewhere in the "Subject:" field.
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.
Backreferences are very slow, and may require exponential
time.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
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ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWggrp
Interface Stability Volatile
NOTES
Source for ggrep is available on http:/opensolaris.org.
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