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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GREP(1P) POSIX Programmer's Manual GREP(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
grep — search a file for a pattern
grep [-E|-F] [-c|-l|-q] [-insvx] -e pattern_list
[-e pattern_list]... [-f pattern_file]... [file...]
grep [-E|-F] [-c|-l|-q] [-insvx] [-e pattern_list]...
-f pattern_file [-f pattern_file]... [file...]
grep [-E|-F] [-c|-l|-q] [-insvx] pattern_list [file...]
The grep utility shall search the input files, selecting lines
matching one or more patterns; the types of patterns are
controlled by the options specified. The patterns are specified by
the -e option, -f option, or the pattern_list operand. The
pattern_list's value shall consist of one or more patterns
separated by <newline> characters; the pattern_file's contents
shall consist of one or more patterns terminated by a <newline>
character. By default, an input line shall be selected if any
pattern, treated as an entire basic regular expression (BRE) as
described in the Base Definitions volume of POSIX.1‐2017, Section
9.3, Basic Regular Expressions, matches any part of the line
excluding the terminating <newline>; a null BRE shall match every
line. By default, each selected input line shall be written to the
standard output.
Regular expression matching shall be based on text lines. Since a
<newline> separates or terminates patterns (see the -e and -f
options below), regular expressions cannot contain a <newline>.
Similarly, since patterns are matched against individual lines
(excluding the terminating <newline> characters) of the input,
there is no way for a pattern to match a <newline> found in the
input.
The grep utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-E Match using extended regular expressions. Treat each
pattern specified as an ERE, as described in the Base
Definitions volume of POSIX.1‐2017, Section 9.4,
Extended Regular Expressions. If any entire ERE pattern
matches some part of an input line excluding the
terminating <newline>, the line shall be matched. A null
ERE shall match every line.
-F Match using fixed strings. Treat each pattern specified
as a string instead of a regular expression. If an input
line contains any of the patterns as a contiguous
sequence of bytes, the line shall be matched. A null
string shall match every line.
-c Write only a count of selected lines to standard output.
-e pattern_list
Specify one or more patterns to be used during the
search for input. The application shall ensure that
patterns in pattern_list are separated by a <newline>.
A null pattern can be specified by two adjacent
<newline> characters in pattern_list. Unless the -E or
-F option is also specified, each pattern shall be
treated as a BRE, as described in the Base Definitions
volume of POSIX.1‐2017, Section 9.3, Basic Regular
Expressions. Multiple -e and -f options shall be
accepted by the grep utility. All of the specified
patterns shall be used when matching lines, but the
order of evaluation is unspecified.
-f pattern_file
Read one or more patterns from the file named by the
pathname pattern_file. Patterns in pattern_file shall
be terminated by a <newline>. A null pattern can be
specified by an empty line in pattern_file. Unless the
-E or -F option is also specified, each pattern shall be
treated as a BRE, as described in the Base Definitions
volume of POSIX.1‐2017, Section 9.3, Basic Regular
Expressions.
-i Perform pattern matching in searches without regard to
case; see the Base Definitions volume of POSIX.1‐2017,
Section 9.2, Regular Expression General Requirements.
-l (The letter ell.) Write only the names of files
containing selected lines to standard output. Pathnames
shall be written once per file searched. If the standard
input is searched, a pathname of "(standardinput)" shall
be written, in the POSIX locale. In other locales,
"standardinput" may be replaced by something more
appropriate in those locales.
-n Precede each output line by its relative line number in
the file, each file starting at line 1. The line number
counter shall be reset for each file processed.
-q Quiet. Nothing shall be written to the standard output,
regardless of matching lines. Exit with zero status if
an input line is selected.
-s Suppress the error messages ordinarily written for
nonexistent or unreadable files. Other error messages
shall not be suppressed.
-v Select lines not matching any of the specified patterns.
If the -v option is not specified, selected lines shall
be those that match any of the specified patterns.
-x Consider only input lines that use all characters in the
line excluding the terminating <newline> to match an
entire fixed string or regular expression to be matching
lines.
The following operands shall be supported:
pattern_list
Specify one or more patterns to be used during the
search for input. This operand shall be treated as if
it were specified as -e pattern_list.
file A pathname of a file to be searched for the patterns. If
no file operands are specified, the standard input shall
be used.
The standard input shall be used if no file operands are
specified, and shall be used if a file operand is '-' and the
implementation treats the '-' as meaning standard input.
Otherwise, the standard input shall not be used. See the INPUT
FILES section.
The input files shall be text files.
The following environment variables shall affect the execution of
grep:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_COLLATE
Determine the locale for the behavior of ranges,
equivalence classes, and multi-character collating
elements within regular expressions.
LC_CTYPE Determine the locale for the interpretation of sequences
of bytes of text data as characters (for example,
single-byte as opposed to multi-byte characters in
arguments and input files) and the behavior of character
classes within regular expressions.
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
If the -l option is in effect, the following shall be written for
each file containing at least one selected input line:
"%s\n", <file>
Otherwise, if more than one file argument appears, and -q is not
specified, the grep utility shall prefix each output line by:
"%s:", <file>
The remainder of each output line shall depend on the other
options specified:
* If the -c option is in effect, the remainder of each output
line shall contain:
"%d\n", <count>
* Otherwise, if -c is not in effect and the -n option is in
effect, the following shall be written to standard output:
"%d:", <line number>
* Finally, the following shall be written to standard output:
"%s", <selected-line contents>
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 One or more lines were selected.
1 No lines were selected.
>1 An error occurred.
If the -q option is specified, the exit status shall be zero if an
input line is selected, even if an error was detected. Otherwise,
default actions shall be performed.
The following sections are informative.
Care should be taken when using characters in pattern_list that
may also be meaningful to the command interpreter. It is safest to
enclose the entire pattern_list argument in single-quotes:
'...'
The -e pattern_list option has the same effect as the pattern_list
operand, but is useful when pattern_list begins with the <hyphen-
minus> delimiter. It is also useful when it is more convenient to
provide multiple patterns as separate arguments.
Multiple -e and -f options are accepted and grep uses all of the
patterns it is given while matching input text lines. (Note that
the order of evaluation is not specified. If an implementation
finds a null string as a pattern, it is allowed to use that
pattern first, matching every line, and effectively ignore any
other patterns.)
The -q option provides a means of easily determining whether or
not a pattern (or string) exists in a group of files. When
searching several files, it provides a performance improvement
(because it can quit as soon as it finds the first match) and
requires less care by the user in choosing the set of files to
supply as arguments (because it exits zero if it finds a match
even if grep detected an access or read error on earlier file
operands).
When using grep to process pathnames, it is recommended that
LC_ALL, or at least LC_CTYPE and LC_COLLATE, are set to POSIX or C
in the environment, since pathnames can contain byte sequences
that do not form valid characters in some locales, in which case
the utility's behavior would be undefined. In the POSIX locale
each byte is a valid single-byte character, and therefore this
problem is avoided.
1. To find all uses of the word "Posix" (in any case) in file
text.mm and write with line numbers:
grep -i -n posix text.mm
2. To find all empty lines in the standard input:
grep ^$
or:
grep -v .
3. Both of the following commands print all lines containing
strings "abc" or "def" or both:
grep -E 'abc|def'
grep -F 'abc
def'
4. Both of the following commands print all lines matching
exactly "abc" or "def":
grep -E '^abc$|^def$'
grep -F -x 'abc
def'
This grep has been enhanced in an upwards-compatible way to
provide the exact functionality of the historical egrep and fgrep
commands as well. It was the clear intention of the standard
developers to consolidate the three greps into a single command.
The old egrep and fgrep commands are likely to be supported for
many years to come as implementation extensions, allowing
historical applications to operate unmodified.
Historical implementations usually silently ignored all but one of
multiply-specified -e and -f options, but were not consistent as
to which specification was actually used.
The -b option was omitted from the OPTIONS section because block
numbers are implementation-defined.
The System V restriction on using - to mean standard input was
omitted.
A definition of action taken when given a null BRE or ERE is
specified. This is an error condition in some historical
implementations.
The -l option previously indicated that its use was undefined when
no files were explicitly named. This behavior was historical and
placed an unnecessary restriction on future implementations. It
has been removed.
The historical BSD grep -s option practice is easily duplicated by
redirecting standard output to /dev/null. The -s option required
here is from System V.
The -x option, historically available only with fgrep, is
available here for all of the non-obsolescent versions.
None.
sed(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Chapter 9, Regular Expressions, Section
12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 GREP(1P)
Pages that refer to this page: awk(1p), cut(1p), paste(1p), sed(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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