xenial (1) grep.1posix.gz

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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.1‐2008,
       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

       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

       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.1‐2008, 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

       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> 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

        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.1‐2008,  Chapter  8,  Environment  Variables,  Chapter  9,  Regular
       Expressions, Section 12.2, Utility Syntax Guidelines

       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 .