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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  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
       output.

       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.

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 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
		 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  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.

       −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 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
		 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.

OPERANDS
       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.

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.  Otherwise, 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 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.

       LC_COLLATE
		 Determine the locale for the behavior of ranges,  equivalence
		 classes,  and multi-character collating elements within regu‐
		 lar 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 speci‐
       fied, 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>

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 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).

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 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.

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 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
       files  to  man page format. To report such errors, see https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			      GREP(1P)
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