GREP(1P) POSIX Programmer's Manual GREP(1P)PROLOG
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.
NAMEgrep — search a file for a pattern
SYNOPSISgrep [−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 termi‐
nated 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.1‐2008, Sec‐
tion 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
Regular expression matching shall be based on text lines. Since a <new‐
line> 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 ter‐
minating <newline> characters) of the input, there is no way for a pat‐
tern to match a <newline> found in the input.
The grep utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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.1‐2008, Section 9.4, Extended Regular Expres‐
sions. 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 con‐
tains any of the patterns as a contiguous sequence of bytes,
the line shall be matched. A null string shall match every
−c Write only a count of selected lines to standard output.
Specify one or more patterns to be used during the search for
input. The application shall ensure that patterns in pat‐
tern_list are separated by a <newline>. A null pattern can
be specified by two adjacent <newline> characters in pat‐
tern_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.1‐2008, 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 evalua‐
tion is unspecified.
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.1‐2008,
Section 9.3, Basic Regular Expressions.
−i Perform pattern matching in searches without regard to case;
see the Base Definitions volume of POSIX.1‐2008, 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 nonexis‐
tent or unreadable files. Other error messages shall not be
−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:
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
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 vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables 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.
Determine the locale for the behavior of ranges, equivalence
classes, and multi-character collating elements within regu‐
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
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
NLSPATH Determine the location of message catalogs for the processing
If the −l option is in effect, the following shall be written for each
file containing at least one selected input line:
Otherwise, if more than one file argument appears, and −q is not speci‐
fied, the grep utility shall prefix each output line by:
The remainder of each output line shall depend on the other options
* If the −c option is in effect, the remainder of each output line
* 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.
The following exit values shall be returned:
0 One or more lines were selected.
1 No lines were selected.
>1 An error occurred.
CONSEQUENCES OF ERRORS
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 op‐
erand, but is useful when pattern_list begins with the <hyphen> delim‐
iter. 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 pat‐
terns 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).
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 −v .
3. Both of the following commands print all lines containing strings
"abc" or "def" or both:
grep −E 'abc|def'
grep −F 'abc
4. Both of the following commands print all lines matching exactly
"abc" or "def":
grep −E '^abc$|^def$'
grep −F −x 'abc
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 appli‐
cations to operate unmodified.
Historical implementations usually silently ignored all but one of mul‐
tiply-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 num‐
bers 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.
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Chapter 9, Regular Expressions, Section 12.2, Utility Syntax
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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
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IEEE/The Open Group 2013 GREP(1P)