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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 dif-
       fer (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...
               [-f pattern_file]...[file...]

       grep [-E| -F][-c| -l| -q][-insvx][-e pattern_list]...
               -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 pat-
       terns 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>s;
       the pattern_file's contents shall consist of one or more patterns terminated by <newline>. 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 IEEE Std 1003.1-2001, 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>s) 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 IEEE Std 1003.1-2001, 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  IEEE Std 1003.1-2001,  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>s  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 IEEE Std 1003.1-2001, Section 9.3, Basic  Regu-
              lar  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 IEEE Std 1003.1-2001, Section 9.3, Basic Regular Expressions.

       -i     Perform  pattern  matching  in  searches  without  regard  to  case;  see the Base Definitions volume of
              IEEE Std 1003.1-2001, 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 "(standard
              input)" shall be written, in the POSIX locale. In other locales, "standard input"  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.


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 only if no file operands are specified. 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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the prece-
              dence 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 ele-
              ments within regular expressions.

       LC_CTYPE
              Determine the locale for the interpretation of sequences of bytes of text data as characters (for  exam-
              ple,  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  writ-
              ten 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, and the -q option is not, the following shall be written for each file contain-
       ing 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>


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 inter-
       preter. 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 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 pat-
       tern, 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 exten-
       sions, 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  behav-
       ior 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  ver-
       sions.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sed

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                             GREP(1P)