GREP(1) General Commands Manual GREP(1)

grep — file pattern searcher

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 . . . ]
Obsolescent Versions:
egrep [ −c | −l ] [−inv] −e pattern_list [file . . . ]
egrep [ −c | −l ] [−inv] −f pattern_file [file . . . ]
egrep [ −c | −l ] [−inv] pattern_list [file . . . ]
fgrep [ −c | −l ] [−invx] −e pattern_list [file . . . ]
fgrep [ −c | −l ] [−invx] −f pattern_file [file . . . ]
fgrep [ −c | −l ] [−invx] pattern_list [file . . . ]

The grep utility shall search the input files, selecting lines matching one or more patterns; the types of patterns shall be 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>s. By default, an input line shall be selected if any pattern, treated as an entire basic regular expression ( BRE ) as described in 2.8.3, matches any part of the line; 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 <newline> separates or terminates patterns (see the −e and −f options below), regular expressions cannot contain a <newline> character. Similarly, since patterns are matched against individual lines of the input, there is no way for a pattern to match a <newline> found in the input. A command invoking the (obsolescent) egrep utility with the −e option specified shall be equivalent to the command:

grep −E [ −c | −l ] [−inv] −e pattern_list [file . . . ] A command invoking the egrep utility with the −f option specified shall be equivalent to the command:

grep −E [ −c | −l ] [−inv] −f pattern_file [file . . . ] A command invoking the egrep utility with the pattern_list specified shall be equivalent to the command:

grep −E [ −c | −l ] [−inv] pattern_list [file . . . ] A command invoking the (obsolescent) fgrep utility with the −e option specified shall be equivalent to the command:

grep −F [ −c | −l ] [−invx] −e pattern_list [file . . . ] A command invoking the fgrep utility with the −f option specified shall be equivalent to the command:

grep −F [ −c | −l ] [−invx] −f pattern_file [file . . . ] A command invoking the fgrep utility with the pattern_list operand specified shall be equivalent to the command:

grep −F [ −c | −l ] [−invx] pattern_list [file . . . ]

The grep utility shall conform to the utility argument syntax guidelines described in 2.10.2. The following options shall be supported by the implementation:

Match using extended regular expressions. Treat each pattern specified as an ERE, as described in 2.8.4. If any entire ERE pattern matches an input line, the line shall be matched. A null ERE shall match every line.

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.

Write only a count of selected lines to standard output.

pattern_list Specify one or more patterns to be used during the search for input. Patterns in pattern_list shall be separated by a <newline>. A null pattern can be specified by two adjacent <newline>s in pattern_list; in the obsolescent forms, adjacent <newline>s in pattern_list produce undefined results. Unless the −E or −F option is also specified, each pattern shall be treated as a BRE, as described in 2.8.3. In the nonobsolescent forms, 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.

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 2.8.3.

Perform pattern matching in searches without regard to case. See 2.8.2.

(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.

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.

Quiet. Do not write anything to the standard output, regardless of matching lines. Exit with zero status if an input line is selected.

Suppress the error messages ordinarily written for nonexistent or unreadable files. Other error messages shall not be suppressed.

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.

Consider only input lines that use all characters in the line to match an entire fixed string or regular expression to be matching lines.

The following operands shall be supported by the implementation:

pattern

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 (see OPTIONS ).

file

A pathname of a file to be searched for the pattern(s). If no file operands are specified, the standard input shall be used.

The standard input shall be used only if no file operands are specified. See Input Files.

The input files shall be text files.

The following environment variables shall affect the execution of grep:

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

This variable shall determine the locale for the behavior of ranges, equivalence classes, and multicharacter collating elements within regular expressions.

This variable shall determine the locale for the interpretation of sequences of bytes of text data as characters (e.g., single- versus multibyte characters in arguments) and the behavior of character classes within regular expressions.

This variable shall determine the language in which messages should be written.

Default.

If the −l option is in effect, and the −q option is not, a single output line 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>

Used only for diagnostic messages.

None.

None.

The grep utility shall exit with one of the following values:

One or more lines were selected.

No lines were selected.

An error occurred.

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.

This grep has been enhanced in an upward-compatible way to provide the exact functionality of the historical egrep and fgrep commands as well. It was the clear intention of the working group 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 existing applications to operate unmodified. To find all uses of the word Posix (in any case) in the file text.mm, and write with line numbers: grep -i -n posix text.mm To find all empty lines in the standard input:

grep ˆ$ or grep -v . Both of the following commands print all lines containing strings abc or def or both:

grep -E ’abc def’ grep -F ’abc def’ Both of the following commands print all lines matching exactly abc or def: grep -E ’ˆabc$ ˆdef$’ grep -F -x ’abc def’

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. Earlier drafts did not show that the −c, −l, and −q options were mutually exclusive. This has been fixed to more closely align with historical practice and documentation. 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. POSIX. 2 requires that the nonobsolescent forms accept multiple −e and −f options and use all of the patterns specified 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 −b option was removed from the Options subclause, since block numbers are implementation dependent. The System V restriction on using − to mean standard input was lifted. A definition of action taken when given a null RE 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 −q option was added at the suggestion of members of the balloting group as 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 will exit zero if it finds a match even if grep detected an access or read error on earlier file operands). The historical 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 nonobsolescent versions.

September 1991 posix.fail