Ubuntu Manpage: grep - search a file for a pattern

NAME

       grep - search a file for a pattern

SYNOPSIS

       grep [-E| -F][-c| -l| -q][-insvx] -e pattern_list...
               [-f pattern_file]...[file...]

       grep [-E| -F][-c| -l| -q][-insvx][-e pattern_list]...
               -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>s; the pattern_file's contents shall consist of one or more patterns terminated  by
       <newline>. 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 IEEE Std 1003.1-2001, 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>s) 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 IEEE Std 1003.1-2001, 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 IEEE Std 1003.1-2001, 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>s 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 IEEE Std 1003.1-2001,
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 IEEE Std 1003.1-2001, Section 9.3, Basic
Regular Expressions.

-i Perform pattern matching in searches without regard to case; see the Base Definitions volume of
IEEE Std 1003.1-2001, 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 "(standard input)" shall be written, in the POSIX locale. In other locales, "standard input"
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 only if no file operands are specified. 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 IEEE Std 1003.1-2001, 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, and the -q option is not, 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.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE/The Open Group                                   2003                                               GREP(P)