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pcregrep man page

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SYNOPSIS

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


DESCRIPTION

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(3) 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 to delimit patterns 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 a 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, followed by a colon. 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. What defines a line boundary is controlled by the -N (--newline) option.

Patterns are limited to 8K or BUFSIZ characters, whichever is the greater. BUFSIZ is defined in <stdio.h>. When there is more than one pattern (specified by the use of -e and/or -f), each pattern is applied to each line in the order in which they are defined, except that all the -e patterns are tried before the -f patterns.

By default, as soon as one pattern matches (or fails to match when -v is used), no further patterns are considered. However, if --colour (or --color) is used to colour the matching substrings, or if --only-matching, --file-offsets, or --line-offsets is used to output only the part of the line that matched (either shown literally, or as an offset), scanning resumes immediately following the match, so that further matches on the same line can be found. If there are multiple patterns, they are all tried on the remainder of the line, but patterns that follow the one that matched are not tried on the earlier part of the line.

This is the same behaviour as GNU grep, but it does mean that the order in which multiple patterns are specified can affect the output when one of the above options is used.

Patterns that can match an empty string are accepted, but empty string matches are never recognized. An example is the pattern "(super)?(man)?", in which all components are optional. This pattern finds all occurrences of both "super" and "man"; the output differs from matching with "super|man" when only the matching substrings are being shown.

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.


SUPPORT FOR COMPRESSED FILES

It is possible to compile pcregrep so that it uses libz or libbz2 to read files whose names end in .gz or .bz2, respectively. You can find out whether your binary has support for one or both of these file types by running it with the --help option. If the appropriate support is not present, files are treated as plain text. The standard input is always so treated.


OPTIONS

The order in which some of the options appear can affect the output. For example, both the -h and -l options affect the printing of file names. Whichever comes later in the command line will be the one that takes effect.

-- 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 from the files that are being scanned; instead output the number of lines that would otherwise have been shown. If no lines are selected, the number zero is output. If several files are are being scanned, a count is output for each of them. However, if the --files-with-matches option is also used, only those files whose counts are greater than zero are listed. When -c is used, 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 parts of a line that matched a pattern should be coloured in the output. By default, the output is not coloured. The value (which is optional, see above) may be "never", "always", or "auto". In the latter case, colouring happens only if the standard output is connected to a terminal. More resources are used when colouring is enabled, because pcregrep has to search for all possible matches in a line, not just one, in order to colour them all.

The colour that is used 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 part(s) 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 regular files whose names match the pattern are excluded. Subdirectories are not excluded by this option; they are searched recursively, subject to the --exclude_dir and --include_dir options. The pattern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

--exclude_dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, any subdirectories whose names match the pattern are excluded. (Note that the \fP--exclude\fP option does not affect subdirectories.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include_dir and --exclude_dir, 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. See also the comments about multiple patterns versus a single pattern with alternatives in the description of -e above.

--file-offsets Instead of showing lines or parts of lines that match, show each match as an offset from the start of the file and a length, separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. This option is mutually exclusive with --line-offsets and --only-matching.

-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; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name.

-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; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name.

--help Output a help message, giving brief details of the command options and file type support, and then 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 regular files whose names match the pattern are included. Subdirectories are always included and searched recursively, subject to the \fP--include_dir\fP and --exclude_dir options. The pattern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

--include_dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, only those subdirectories whose names match the pattern are included. (Note that the --include option does not affect subdirectories.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include_dir and --exclude_dir, 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 normally stops as soon as a matching line is found in a file. However, if the -c (count) option is also used, matching continues in order to obtain the correct count, and those files that have at least one match are listed along with their counts. Using this option with -c is a way of suppressing the listing of files with no matches.

--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.

--line-buffered When this option is given, input is read and processed line by line, and the output is flushed after each write. By default, input is read in large chunks, unless pcregrep can determine that it is reading from a terminal (which is currently possible only in Unix environments). Output to terminal is normally automatically flushed by the operating system. This option can be useful when the input or output is attached to a pipe and you do not want pcregrep to buffer up large amounts of data. However, its use will affect performance, and the -M (multiline) option ceases to work.

--line-offsets Instead of showing lines or parts of lines that match, show each match as a line number, the offset from the start of the line, and a length. The line number is terminated by a colon (as usual; see the -n option), and the offset and length are separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. This option is mutually exclusive with --file-offsets and --only-matching.

--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. This option does not work when input is read line by line (see \fP--line-buffered\fP.)

-N newline-type, --newline=newline-type The PCRE library supports five different conventions for indicating the ends of lines. They are the single-character sequences CR (carriage return) and LF (linefeed), the two-character sequence CRLF, an "anycrlf" convention, which recognizes any of the preceding three types, and an "any" convention, in which any Unicode line ending sequence is assumed to end a line. The Unicode sequences are the three just mentioned, plus VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).

When the PCRE library is built, a default line-ending sequence is specified. This is normally the standard sequence for the operating system. Unless otherwise specified by this option, pcregrep uses the library's default. The possible values for this option are CR, LF, CRLF, ANYCRLF, or ANY. This makes it possible to use pcregrep on files that have come from other environments without having to modify their line endings. If the data that is being scanned does not agree with the convention set by this option, pcregrep may behave in strange ways.

-n, --line-number Precede each output line by its line number in the file, followed by a colon for matching lines or a hyphen for context lines. If the filename is also being output, it precedes the line number. This option is forced if --line-offsets is used.

-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. If there is more than one match in a line, each of them is shown separately. If -o is combined with -v (invert the sense of the match to find non-matching lines), no output is generated, but the return code is set appropriately. This option is mutually exclusive with --file-offsets and --line-offsets.

-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.


NEWLINES

The -N (--newline) option allows pcregrep to scan files with different newline conventions from the default. However, the setting of this option does not affect the way in which pcregrep writes information to the standard error and output streams. It uses the string "\n" in C printf() calls to indicate newlines, relying on the C I/O library to convert this to an appropriate sequence if the output is sent to a file.


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. If both the -c and -l options are given, GNU grep lists only file names, without counts, but pcregrep gives the counts.


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.


SEE ALSO

pcrepattern(3), pcretest(1).


AUTHOR

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


REVISION

Last updated: 21 May 2010
Copyright © 1997-2010 University of Cambridge.

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