pcregrep

pcregrep - a grep with Perl-compatible regular expressions.

pcregrep [options] [long options] [pattern] [path1 path2 ...]

pcregrep searches files for character patterns, in the same way as other grep commands do, but it uses the PCRE regular expression library to support patterns that are compatible with the regular expressions of Perl 5. See pcrepattern for a full description of syntax and semantics of the regular expressions that PCRE supports.

Patterns, whether supplied on the command line or in a separate file, are given without delimiters. For example:

pcregrep Thursday /etc/motd

If you attempt to use delimiters (for example, by surrounding a pattern with slashes, as is common in Perl scripts), they are interpreted as part of the pattern. Quotes can of course be used on the command line because they are interpreted by the shell, and indeed they are required if a pattern contains white space or shell metacharacters.

The first argument that follows any option settings is treated as the single pattern to be matched when neither -e nor -f is present. Conversely, when one or both of these options are used to specify patterns, all arguments are treated as path names. At least one of -e, -f, or an argument pattern must be provided.

If no files are specified, pcregrep reads the standard input. The standard input can also be referenced by a name consisting of a single hyphen. For example:

pcregrep some-pattern /file1 - /file3

By default, each line that matches the pattern is copied to the standard output, and if there is more than one file, the file name is output at the start of each line. However, there are options that can change how pcregrep behaves. In particular, the -M option makes it possible to search for patterns that span line boundaries.

Patterns are limited to 8K or BUFSIZ characters, whichever is the greater. BUFSIZ is defined in <stdio.h>.

If the LC_ALL or LC_CTYPE environment variable is set, pcregrep uses the value to set a locale when calling the PCRE library. The --locale option can be used to override this.

Options

--

This terminate the list of options. It is useful if the next item on the command line starts with a hyphen but is not an option. This allows for the processing of patterns and filenames that start with hyphens.

-A number, --after-context=number

Output number lines of context after each matching line. If filenames and/or line numbers are being output, a hyphen separator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of following text available for context output.

-B number, --before-context=number

Output number lines of context before each matching line. If filenames and/or line numbers are being output, a hyphen separator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of preceding text available for context output.

-C number, --context=number

Output number lines of context both before and after each matching line. This is equivalent to setting both -A and -B to the same value.

-c, --count

Do not output individual lines; instead just output a count of the number of lines that would otherwise have been output. If several files are given, a count is output for each of them. In this mode, the -A, -B, and -C options are ignored.

--colour, --color

If this option is given without any data, it is equivalent to "--colour=auto". If data is required, it must be given in the same shell item, separated by an equals sign.

--colour=value, --color=value

This option specifies under what circumstances the part of a line that matched a pattern should be coloured in the output. The value may be "never" (the default), "always", or "auto". In the latter case, colouring happens only if the standard output is connected to a terminal. The colour can be specified by setting the environment variable PCREGREP_COLOUR or PCREGREP_COLOR. The value of this variable should be a string of two numbers, separated by a semicolon. They are copied directly into the control string for setting colour on a terminal, so it is your responsibility to ensure that they make sense. If neither of the environment variables is set, the default is "1;31", which gives red.

-D action, --devices=action

If an input path is not a regular file or a directory, "action" specifies how it is to be processed. Valid values are "read" (the default) or "skip" (silently skip the path).

-d action, --directories=action

If an input path is a directory, "action" specifies how it is to be processed. Valid values are "read" (the default), "recurse" (equivalent to the -r option), or "skip" (silently skip the path). In the default case, directories are read as if they were ordinary files. In some operating systems the effect of reading a directory like this is an immediate end-of-file.

-e pattern, --regex=pattern,

--regexp=pattern Specify a pattern to be matched. This option can be used multiple times in order to specify several patterns. It can also be used as a way of specifying a single pattern that starts with a hyphen. When -e is used, no argument pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. They are applied to each line in the order in which they are defined until one matches (or fails to match if -v is used). If -f is used with -e, the command line patterns are matched first, followed by the patterns from the file, independent of the order in which these options are specified. Note that multiple use of -e is not the same as a single pattern with alternatives. For example, X|Y finds the first character in a line that is X or Y, whereas if the two patterns are given separately, pcregrep finds X if it is present, even if it follows Y in the line. It finds Y only if there is no X in the line. This really matters only if you are using -o to show the portion of the line that matched.

--exclude=pattern

When pcregrep is searching the files in a directory as a consequence of the -r (recursive search) option, any files whose names match the pattern are excluded. The pattern is a PCRE regular expression. If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

-F, --fixed-strings

Interpret each pattern as a list of fixed strings, separated by newlines, instead of as a regular expression. The -w (match as a word) and -x (match whole line) options can be used with -F. They apply to each of the fixed strings. A line is selected if any of the fixed strings are found in it (subject to -w or -x, if present).

-f filename, --file=filename

Read a number of patterns from the file, one per line, and match them against each line of input. A data line is output if any of the patterns match it. The filename can be given as "-" to refer to the standard input. When -f is used, patterns specified on the command line using -e may also be present; they are tested before the file's patterns. However, no other pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. Trailing white space is removed from each line, and blank lines are ignored. An empty file contains no patterns and therefore matches nothing.

-H, --with-filename

Force the inclusion of the filename at the start of output lines when searching a single file. By default, the filename is not shown in this case. For matching lines, the filename is followed by a colon and a space; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name without a space.

-h, --no-filename

Suppress the output filenames when searching multiple files. By default, filenames are shown when multiple files are searched. For matching lines, the filename is followed by a colon and a space; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name without a space.

--help

Output a brief help message and exit.

-i, --ignore-case

Ignore upper/lower case distinctions during comparisons.

--include=pattern

When pcregrep is searching the files in a directory as a consequence of the -r (recursive search) option, only those files whose names match the pattern are included. The pattern is a PCRE regular expression. If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

-L, --files-without-match

Instead of outputting lines from the files, just output the names of the files that do not contain any lines that would have been output. Each file name is output once, on a separate line.

-l, --files-with-matches

Instead of outputting lines from the files, just output the names of the files containing lines that would have been output. Each file name is output once, on a separate line. Searching stops as soon as a matching line is found in a file.

--label=name

This option supplies a name to be used for the standard input when file names are being output. If not supplied, "(standard input)" is used. There is no short form for this option.

--locale=locale-name

This option specifies a locale to be used for pattern matching. It overrides the value in the LC_ALL or LC_CTYPE environment variables. If no locale is specified, the PCRE library's default (usually the "C" locale) is used. There is no short form for this option.

-M, --multiline

Allow patterns to match more than one line. When this option is given, patterns may usefully contain literal newline characters and internal occurrences of ^ and $ characters. The output for any one match may consist of more than one line. When this option is set, the PCRE library is called in "multiline" mode. There is a limit to the number of lines that can be matched, imposed by the way that pcregrep buffers the input file as it scans it. However, pcregrep ensures that at least 8K characters or the rest of the document (whichever is the shorter) are available for forward matching, and similarly the previous 8K characters (or all the previous characters, if fewer than 8K) are guaranteed to be available for lookbehind assertions.

-n, --line-number

Precede each output line by its line number in the file, followed by a colon and a space for matching lines or a hyphen and a space for context lines. If the filename is also being output, it precedes the line number.

-o, --only-matching

Show only the part of the line that matched a pattern. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored.

-q, --quiet

Work quietly, that is, display nothing except error messages. The exit status indicates whether or not any matches were found.

-r, --recursive

If any given path is a directory, recursively scan the files it contains, taking note of any --include and --exclude settings. By default, a directory is read as a normal file; in some operating systems this gives an immediate end-of-file. This option is a shorthand for setting the -d option to "recurse".

-s, --no-messages

Suppress error messages about non-existent or unreadable files. Such files are quietly skipped. However, the return code is still 2, even if matches were found in other files.

-u, --utf-8

Operate in UTF-8 mode. This option is available only if PCRE has been compiled with UTF-8 support. Both patterns and subject lines must be valid strings of UTF-8 characters.

-V, --version

Write the version numbers of pcregrep and the PCRE library that is being used to the standard error stream.

-v, --invert-match

Invert the sense of the match, so that lines which do not match any of the patterns are the ones that are found.

-w, --word-regex, --word-regexp

Force the patterns to match only whole words. This is equivalent to having \b at the start and end of the pattern.

-x, --line-regex, --line-regexp

Force the patterns to be anchored (each must start matching at the beginning of a line) and in addition, require them to match entire lines. This is equivalent to having ^ and $ characters at the start and end of each alternative branch in every pattern.

Environment Variables

The environment variables LC_ALL and LC_CTYPE are examined, in that order, for a locale. The first one that is set is used. This can be overridden by the --locale option. If no locale is set, the PCRE library's default (usually the "C" locale) is used.

Options Compatibility

The majority of short and long forms of pcregrep's options are the same as in the GNU grep program. Any long option of the form --xxx-regexp (GNU terminology) is also available as --xxx-regex (PCRE terminology). However, the --locale, -M, --multiline, -u, and --utf-8 options are specific to pcregrep.

Options With Data

There are four different ways in which an option with data can be specified. If a short form option is used, the data may follow immediately, or in the next command line item. For example:

-f/some/file -f /some/file

If a long form option is used, the data may appear in the same command line item, separated by an equals character, or (with one exception) it may appear in the next command line item. For example:

--file=/some/file --file /some/file

Note, however, that if you want to supply a file name beginning with ~ as data in a shell command, and have the shell expand ~ to a home directory, you must separate the file name from the option, because the shell does not treat ~ specially unless it is at the start of an item.

The exception to the above is the --colour (or --color) option, for which the data is optional. If this option does have data, it must be given in the first form, using an equals character. Otherwise it will be assumed that it has no data.

Matching Errors

It is possible to supply a regular expression that takes a very long time to fail to match certain lines. Such patterns normally involve nested indefinite repeats, for example: (a+)*\d when matched against a line of a's with no final digit. The PCRE matching function has a resource limit that causes it to abort in these circumstances. If this happens, pcregrep outputs an error message and the line that caused the problem to the standard error stream. If there are more than 20 such errors, pcregrep gives up.

Diagnostics

Exit status is 0 if any matches were found, 1 if no matches were found, and 2 for syntax errors and non-existent or inacessible files (even if matches were found in other files) or too many matching errors. Using the -s option to suppress error messages about inaccessble files does not affect the return code.

Author

Philip Hazel
University Computing Service
Cambridge CB2 3QG, England.

Last updated: 23 January 2006
Copyright (c) 1997-2006 University of Cambridge.

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