GREP(1)                    POSIX Programmer's Manual                   GREP(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 ""((ssttaannddaarrddinput)" shall be written, in the POSIX
                 locale. In other locales, ""ssttaannddaarrddinput" 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 .



IEEE/The Open Group                  2017                              GREP(1)
