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LINUX Web Hosting Commands and tools grepSYNOPSIS
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 con-
tiguous 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 con-
tiguous 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.
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 pro-
cess 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 pat-
terns beginning with -.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, sepa-
rated by newlines, any of which is to be matched.
-P, --perl-regexp Interpret PATTERN as a Perl regu-
lar 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
-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.
--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 perfor-
mance. However, --mmap can cause undefined behav-
ior (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 espe-
cially 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 penal-
ity.
-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
-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.
-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-Win-
dows.
-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-match-
ing 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 charac-
ter. Similarly, it must be either at the end of
the line or followed by a non-word constituent
character. Word-constituent characters are let-
ters, digits, and the underscore.
-x, --line-regexp
Select only those matches that exactly match the
whole line.
-y Obsolete synonym for -i.
-Z, --null
to arithmetic expressions, by using various operators to
combine 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
syntax. In other implementations, basic regular expres-
sions 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 expres-
sions 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 char-
acter 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 [aBbC-
cDd], for example. To obtain the traditional interpreta-
tion 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 prede-
fined 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 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
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 concate-
nating two substrings that respectively match the concate-
nated subexpressions.
Two regular expressions may be joined by the infix opera-
tor |; the resulting regular expression matches any string
matching either subexpression.
Repetition takes precedence over concatenation, which in
turn takes precedence over alternation. A whole subex-
pression 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 assum-
ing 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 LC_foo is specified by examining the three envi-
ronment variables LC_ALL, LC_foo, LANG, in that order.
The first of these variables that is set specifies the
explicit options. Option specifications are sepa-
rated 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; other-
wise, 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 diag-
nosed 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 com-
mand it runs, specifying which operands are the
results of file name wildcard expansion and there-
fore should not be treated as options. This behav-
ior 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
GNU Project 2002/01/22 GREP(1)
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