This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

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  -epattern_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.

Asynchronous Events

       Default.

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.

       Thefollowingsectionsareinformative.

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 .

IEEE/The Open Group                                   2017                                          GREP(1POSIX)

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,
       Section9.3, BasicRegularExpressions, 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.

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, Section8.2, InternationalizationVariables 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.

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'

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.

Extended Description

       None.

Future Directions

       None.

Input Files

       The input files shall be text files.

Name

       grep — search a file for a pattern

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 -epattern_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.

Options

The grep utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section12.2, UtilitySyntaxGuidelines.

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, Section9.4, ExtendedRegularExpressions. 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.

-epattern_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, Section9.3, BasicRegularExpressions. 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.

-fpattern_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, Section9.3,
BasicRegularExpressions.

-i Perform pattern matching in searches without regard to case; see the Base Definitions volume of
POSIX.1‐2017, Section9.2, RegularExpressionGeneralRequirements.

-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.

Output Files

       None.

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.

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.

Stderr

       The standard error shall be used only for diagnostic messages.

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.

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:", <linenumber>

        *  Finally, the following shall be written to standard output:

               "%s", <selected-linecontents>

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...]