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. 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 containing -- 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. 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.
--colour[=WHEN], --color[=WHEN]
Surround the matching string with the marker find in GREP_COLOR environment variable. WHEN may
be `never', `always', or `auto'
-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, --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 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 newlines, any of which is to be
matched. -P, --perl-regexp Interpret PATTERN 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 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 nor-mally normally
mally 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 con-text context
text 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 unde-fined undefined
fined 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.
-o, --only-matching
Show only the part of a matching line that matches PATTERN.
--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-buffered
Turns on line buffering. However, this can be a performance penalty.
-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=PATTERN
Recurse in directories only searching file matching PATTERN.
--exclude=PATTERN
Recurse in directories skip file matching PATTERN.
-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 reg-ular regular
ular expressions with ^ and $ work correctly). Specifying -U overrules this guesswork, caus-ing causing
ing 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.
-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 match-ing matching
ing substring must either be at the beginning of the line, or preceded by a non-word con-stituent constituent
stituent character. Similarly, it must be either at the end of the line or followed by a non-word nonword
word constituent character. Word-constituent characters are letters, digits, and the under-score. underscore.
score.
-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 con-tain contain
tain newline characters.
REGULAR EXPRESSIONS
A regular expression is a pattern that describes a set of strings. Regular expressions are con-structed constructed
structed analogously to arithmetic expressions, by using various operators to combine smaller expres-sions. expressions.
sions.
Grep understands two different versions of regular expression syntax: "basic" and "extended." In
GNU grep, there is no difference in available functionality using either syntax. In other implemen-tations, implementations,
tations, 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 tradi-tional traditional
tional interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environ-ment environment
ment 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 [0-9A-Za-z], except the latter form depends upon the C 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 delimit-ing delimiting
ing 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 begin-ning beginning
ning 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 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 subexpression.
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 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
{.
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.
For more information see re_format(7).
ENVIRONMENT VARIABLES
Grep's behavior is affected by the following environment variables.
A locale 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 Brazilian Portuguese is used for the LC_MESSAGES
locale. The C locale is used if none of these environment variables are set, or if the locale cata-log catalog
log 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. For
example, if GREP_OPTIONS 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.
GREP_COLOR
Specifies the marker for highlighting.
LC_ALL, LC_COLLATE, LANG
These variables specify the LC_COLLATE locale, which determines the collating sequence used to
interpret range expressions like [a-z].
LC_ALL, LC_CTYPE, LANG
These variables specify the LC_CTYPE locale, which determines the type of characters, e.g.,
which characters are whitespace.
LC_ALL, LC_MESSAGES, LANG
These variables specify the LC_MESSAGES locale, 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.2 requires; otherwise, grep behaves more like other GNU pro-grams. programs.
grams. 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_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.
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.
GNU Project 2002/01/22 GREP(1)
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