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POSIX 1003.1 - man page for grep (posix section 1p)

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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.

NAME
       grep -- search a file for a pattern

SYNOPSIS
       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...]

DESCRIPTION
       The  grep  utility shall search the input files, selecting lines matching one or more pat-
       terns; 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  pat-
       tern_file's contents shall consist of one or more patterns terminated by a <newline> char-
       acter. 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, Section 9.3, Basic Regular Expressions, matches any part of the line exclud-
       ing  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.

OPTIONS
       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 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  contigu-
		 ous  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 appli-
		 cation  shall ensure that patterns in pattern_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 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.1-2008, Section 9.3, Basic Regular Expressions.

       -i	 Perform  pattern matching in searches without regard to case; see the Base Defi-
		 nitions volume of POSIX.1-2008, Section 9.2, Regular Expression General Require-
		 ments.

       -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 stan-
		 dard 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  pro-
		 cessed.

       -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  pat-
		 terns.

       -x	 Consider only input lines that use all characters in the line excluding the ter-
		 minating <newline> to match an entire fixed string or regular expression  to  be
		 matching lines.

OPERANDS
       The following operands shall be supported:

       pattern_list
		 Specify one or more patterns to be used during the search for input.  This oper-
		 and 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.

STDIN
       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.  Oth-
       erwise, the standard input shall not be used.  See the INPUT FILES section.

INPUT FILES
       The input files shall be text files.

ENVIRONMENT VARIABLES
       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.1-2008,  Section  8.2,  Interna-
		 tionalization	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  inter-
		 nationalization 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.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       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 util-
       ity 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>

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       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.

APPLICATION USAGE
       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 sin-
       gle-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> 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 op-
       erands).

EXAMPLES
	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'

RATIONALE
       This grep has been enhanced in an upwards-compatible way to provide the exact  functional-
       ity  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  implementa-
       tion-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  explic-
       itly  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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sed

       The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Chapter  9,
       Regular Expressions, Section 12.2, Utility Syntax Guidelines

COPYRIGHT
       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 Electrical 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 discrep-
       ancy 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 files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group			       2013					 GREP(1P)
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