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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 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.

OPTIONS

       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.

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 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.

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
       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 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.

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 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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sed

       The Base Definitions volume of POSIX.1‐2017, 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
       1003.1-2017, 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 .