GREP(1)GREP(1)NAME
grep, egrep, fgrep - print lines matching a pattern
SYNOPSIS
grep [options] PATTERN [FILE...]
grep [options] [-e PATTERN | -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 containing a match to the
given PATTERN. By default, grep prints the matching lines.
In addition, two variant programs egrep and fgrep are available. 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.
-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.
-C [NUM], -NUM, --context[=NUM]
Print NUM lines (default 2) of output context.
-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 mes‐
sage 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. Warning: grep
--binary-files=text might output binary garbage, which can have
nasty side effects if the output is a terminal and if the termi‐
nal driver interprets some of it as commands.
-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.
-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, direc‐
tories 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 PATTERN as an extended regular expression (see below).
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern; useful to protect patterns beginning
with -.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, separated by new‐
lines, any of which is to be matched.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. The empty file con‐
tains zero patterns, and therefore matches nothing.
-G, --basic-regexp
Interpret PATTERN as a basic regular expression (see below).
This is the default.
-H, --with-filename
Print the filename for each match.
-h, --no-filename
Suppress the prefixing of filenames on output when multiple
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 PATTERN 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.
--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 operating, or if an I/O error occurs.
-n, --line-number
Prefix each line of output with the line number within its input
file.
-q, --quiet, --silent
Quiet; suppress normal output. The scanning will stop on the
first match. Also see the -s or --no-messages option below.
-r, --recursive
Read all files under each directory, recursively; this is equiv‐
alent to the -d recurse option.
-s, --no-messages
Suppress error messages about nonexistent or unreadable files.
Portability note: unlike GNU grep, traditional grep did not con‐
form 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 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-Win‐
dows.
-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 ver‐
sion 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 preceded by a non-word con‐
stituent 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 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.
REGULAR EXPRESSIONS
A regular expression is a pattern that describes a set of strings.
Regular expressions are constructed analogously to arithmetic expres‐
sions, by using various operators to combine smaller expressions.
Grep understands two different versions of regular expression syntax:
“basic” and “extended.” In GNU grep, there is no difference in avail‐
able functionality using either syntax. 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 list of characters enclosed by [ and ] 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. A range of charac‐
ters may be specified by giving the first and last characters, sepa‐
rated by a hyphen. Finally, certain named classes of characters are
predefined. Their names are self explanatory, and they are [:alnum:],
[:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:],
[:punct:], [:space:], [:upper:], and [:xdigit:]. For example,
[[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the
POSIX locale and the ASCII 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
metacharacters 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.
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 oper‐
ators:
? 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 concatenating 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 subex‐
pression.
Repetition takes precedence over concatenation, which in turn takes
precedence over alternation. A whole subexpression may be enclosed in
parentheses to override these precedence rules.
The backreference \n, where n is a single digit, matches the substring
previously matched by the nth parenthesized subexpression of the regu‐
lar 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 {.
GNU egrep attempts to support traditional usage by assuming that { is
not special if it would be the start of an invalid interval specifica‐
tion. 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_OPTIONS
This variable specifies default options to be placed in front of
any explicit options. For example, if GREP_OPTIONS is
'--binary-files=without-match --directories=skip', grep behaves
as if the two options --binary-files=without-match and --direc‐
tories=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.
LC_ALL, LC_MESSAGES, LANG
These variables specify the LC_MESSAGES locale, which determines
the language that grep uses for messages. The locale is deter‐
mined by the first of these variables that is set. American
English is used if none of these environment variables are set,
or if the message catalog is not installed, or if grep was not
compiled with national language support (NLS).
LC_ALL, LC_CTYPE, LANG
These variables specify the LC_CTYPE locale, which determines
the type of characters, e.g., which characters are whitespace.
The locale is determined by the first of these variables that is
set. The POSIX 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).
POSIXLY_CORRECT
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”. POSIXLY_CORRECT also disables _N_GNU_nonop‐
tion_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 com‐
mand 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.
DIAGNOSTICS
Normally, exit status is 0 if matches were found, and 1 if no matches
were found. (The -v option inverts the sense of the exit status.)
Exit status is 2 if there were syntax errors in the pattern, inaccessi‐
ble input files, or other system errors.
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 {m,n} 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.
GNU Project 2002/04/30 GREP(1)
