PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       grep — search a file for a pattern

SYNOPSIS         top

       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         top

       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.1‐2008, 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         top

       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 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.1‐2008,
                 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 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.1‐2008, 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
                 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         top

       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         top

       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         top

       The input files shall be text files.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       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         top

       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>
       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).

EXAMPLES         top

        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         top

       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         top

       None.

SEE ALSO         top

       sed(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Chapter 9, Regular Expressions, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                            GREP(1P)

Pages that refer to this page: awk(1p)cut(1p)paste(1p)sed(1p)