pcre2grep man page

pcre2grep — a grep with Perl-compatible regular expressions.

Synopsis

pcre2grep [options] [long options] [pattern] [path1 path2 ...]

Description

pcre2grep searches files for character patterns, in the same way as other grep commands do, but it uses the PCRE2 regular expression library to support patterns that are compatible with the regular expressions of Perl 5. See pcre2syntax(3) for a quick-reference summary of pattern syntax, or pcre2pattern(3) for a full description of the syntax and semantics of the regular expressions that PCRE2 supports.

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

pcre2grep 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 quotes 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, pcre2grep reads the standard input. The standard input can also be referenced by a name consisting of a single hyphen. For example:

pcre2grep some-pattern file1 - file3

Input files are searched line by line. 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 pcre2grep behaves. In particular, the -M option makes it possible to search for strings that span line boundaries. What defines a line boundary is controlled by the -N (--newline) option.

The amount of memory used for buffering files that are being scanned is controlled by a parameter that can be set by the --buffer-size option. The default value for this parameter is specified when pcre2grep is built, with the default default being 20K. A block of memory three times this size is used (to allow for buffering "before" and "after" lines). An error occurs if a line overflows the buffer.

Patterns can be no longer than 8K or BUFSIZ bytes, 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 a line, 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 behaviour means that the order in which multiple patterns are specified can affect the output when one of the above options is used. This is no longer the same behaviour as GNU grep, which now manages to display earlier matches for later patterns (as long as there is no overlap).

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, pcre2grep uses the value to set a locale when calling the PCRE2 library. The --locale option can be used to override this.

Support for Compressed Files

It is possible to compile pcre2grep 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.

Binary Files

By default, a file that contains a binary zero byte within the first 1024 bytes is identified as a binary file, and is processed specially. (GNU grep also identifies binary files in this manner.) See the --binary-files option for a means of changing the way binary files are handled.

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. Similarly, except where noted below, if an option is given twice, the later setting is used. Numerical values for options may be followed by K or M, to signify multiplication by 1024 or 1024*1024 respectively.

--
This terminates 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 file names that start with hyphens.
-A number, --after-context=number
Output number lines of context after each matching line. If file names 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, pcre2grep guarantees to have up to 8K of following text available for context output.
-a, --text
Treat binary files as text. This is equivalent to --binary-files=text.
-B number, --before-context=number
Output number lines of context before each matching line. If file names 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, pcre2grep guarantees to have up to 8K of preceding text available for context output.
--binary-files=word
Specify how binary files are to be processed. If the word is "binary" (the default), pattern matching is performed on binary files, but the only output is "Binary file <name> matches" when a match succeeds. If the word is "text", which is equivalent to the -a or --text option, binary files are processed in the same way as any other file. In this case, when a match succeeds, the output may be binary garbage, which can have nasty effects if sent to a terminal. If the word is "without-match", which is equivalent to the -I option, binary files are not processed at all; they are assumed not to be of interest and are skipped without causing any output or affecting the return code.
--buffer-size=number
Set the parameter that controls how much memory is used for buffering files that are being scanned.
-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 lines from the files that are being scanned; instead output the number of matches (or non-matches if -v is used) that would otherwise have caused lines to be shown. By default, this count is the same as the number of suppressed lines, but if the -M (multiline) option is used (without -v), there may be more suppressed lines than the number of matches.

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 pcre2grep 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 PCRE2GREP_COLOUR or PCRE2GREP_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 in non-Windows environments, for compatibility with GNU grep), "recurse" (equivalent to the -r option), or "skip" (silently skip the path, the default in Windows environments). In the "read" 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; in others it may provoke an error.
-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 no limit to the number of patterns. They are applied to each line in the order in which they are defined until one matches.

If -f is used with -e, the command line patterns are matched first, followed by the patterns from the file(s), 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, with X first, pcre2grep 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 matters only if you are using -o or --colo(u)r to show the part(s) of the line that matched.
--exclude=pattern
Files (but not directories) whose names match the pattern are skipped without being processed. This applies to all files, whether listed on the command line, obtained from --file-list, or by scanning a directory. The pattern is a PCRE2 regular expression, and is matched against the final component of the file name, not the entire path. The -F, -w, and -x options do not apply to this pattern. The option may be given any number of times in order to specify multiple patterns. If a file name matches both an --include and an --exclude pattern, it is excluded. There is no short form for this option.
--exclude-from=filename
Treat each non-empty line of the file as the data for an --exclude option. What constitutes a newline when reading the file is the operating system's default. The --newline option has no effect on this option. This option may be given more than once in order to specify a number of files to read.
--exclude-dir=pattern
Directories whose names match the pattern are skipped without being processed, whatever the setting of the --recursive option. This applies to all directories, whether listed on the command line, obtained from --file-list, or by scanning a parent directory. The pattern is a PCRE2 regular expression, and is matched against the final component of the directory name, not the entire path. The -F, -w, and -x options do not apply to this pattern. The option may be given any number of times in order to specify more than one pattern. If a directory matches both --include-dir and --exclude-dir, it is excluded. There is no short form for this option.
-F, --fixed-strings
Interpret each data-matching pattern as a list of fixed strings, separated by newlines, instead of as a regular expression. What constitutes a newline for this purpose is controlled by the --newline option. 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). This option applies only to the patterns that are matched against the contents of files; it does not apply to patterns specified by any of the --include or --exclude options.
-f filename, --file=filename
Read patterns from the file, one per line, and match them against each line of input. What constitutes a newline when reading the file is the operating system's default. The --newline option has no effect on this option. 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.

If this option is given more than once, all the specified files are read. A data line is output if any of the patterns match it. A file name 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 the names of paths to be searched.
--file-list=filename
Read a list of files and/or directories that are to be scanned from the given file, one per line. Trailing white space is removed from each line, and blank lines are ignored. These paths are processed before any that are listed on the command line. The file name can be given as "-" to refer to the standard input. If --file and --file-list are both specified as "-", patterns are read first. This is useful only when the standard input is a terminal, from which further lines (the list of files) can be read after an end-of-file indication. If this option is given more than once, all the specified files are read.
--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 file name at the start of output lines when searching a single file. By default, the file name is not shown in this case. For matching lines, the file name 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. When the -M option causes a pattern to match more than one line, only the first is preceded by the file name.
-h, --no-filename
Suppress the output file names when searching multiple files. By default, file names are shown when multiple files are searched. For matching lines, the file name 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. Anything else on the command line is ignored.
-I
Ignore binary files. This is equivalent to --binary-files=without-match.
-i, --ignore-case
Ignore upper/lower case distinctions during comparisons.
--include=pattern
If any --include patterns are specified, the only files that are processed are those that match one of the patterns (and do not match an --exclude pattern). This option does not affect directories, but it applies to all files, whether listed on the command line, obtained from --file-list, or by scanning a directory. The pattern is a PCRE2 regular expression, and is matched against the final component of the file name, not the entire path. The -F, -w, and -x options do not apply to this pattern. The option may be given any number of times. If a file name matches both an --include and an --exclude pattern, it is excluded. There is no short form for this option.
--include-from=filename
Treat each non-empty line of the file as the data for an --include option. What constitutes a newline for this purpose is the operating system's default. The --newline option has no effect on this option. This option may be given any number of times; all the files are read.
--include-dir=pattern
If any --include-dir patterns are specified, the only directories that are processed are those that match one of the patterns (and do not match an --exclude-dir pattern). This applies to all directories, whether listed on the command line, obtained from --file-list, or by scanning a parent directory. The pattern is a PCRE2 regular expression, and is matched against the final component of the directory name, not the entire path. The -F, -w, and -x options do not apply to this pattern. The option may be given any number of times. If a directory 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 pcre2grep can determine that it is reading from a terminal (which is currently possible only in Unix-like 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 pcre2grep 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 PCRE2 library's default (usually the "C" locale) is used. There is no short form for this option.
--match-limit=number
Processing some regular expression patterns can require a very large amount of memory, leading in some cases to a program crash if not enough is available. Other patterns may take a very long time to search for all possible matching strings. The pcre2_match() function that is called by pcre2grep to do the matching has two parameters that can limit the resources that it uses.

The --match-limit option provides a means of limiting resource usage when processing patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats. Internally, PCRE2 uses a function called match() which it calls repeatedly (sometimes recursively). The limit set by --match-limit is imposed on the number of times this function is called during a match, which has the effect of limiting the amount of backtracking that can take place.

The --recursion-limit option is similar to --match-limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursive calls, which in turn limits the amount of memory that can be used. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recursive. This limit is of use only if it is set smaller than --match-limit.

There are no short forms for these options. The default settings are specified when the PCRE2 library is compiled, with the default default being 10 million.
-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 a successful match may consist of more than one line. The first is the line in which the match started, and the last is the line in which the match ended. If the matched string ends with a newline sequence the output ends at the end of that line.

When this option is set, the PCRE2 library is called in "multiline" mode. This allows a matched string to extend past the end of a line and continue on one or more subsequent lines. However, pcre2grep still processes the input line by line. Once a match has been handled, scanning restarts at the beginning of the next line, just as it does when -M is not present. This means that it is possible for the second or subsequent lines in a multiline match to be output again as part of another match.

The newline sequence that separates multiple lines must be matched as part of the pattern. For example, to find the phrase "regular expression" in a file where "regular" might be at the end of a line and "expression" at the start of the next line, you could use this command:

pcre2grep -M 'regular\s+expression' <file>

The \s escape sequence matches any white space character, including newlines, and is followed by + so as to match trailing white space on the first line as well as possibly handling a two-character newline sequence.

There is a limit to the number of lines that can be matched, imposed by the way that pcre2grep buffers the input file as it scans it. However, pcre2grep ensures that at least 8K characters or the rest of the file (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. The -M option does not work when input is read line by line (see --line-buffered.)
-N newline-type, --newline=newline-type
The PCRE2 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 (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).

When the PCRE2 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, pcre2grep uses the library's default. The possible values for this option are CR, LF, CRLF, ANYCRLF, or ANY. This makes it possible to use pcre2grep to scan 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, pcre2grep may behave in strange ways. Note that this option does not apply to files specified by the -f, --exclude-from, or --include-from options, which are expected to use the operating system's standard newline sequence.
-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 file name is also being output, it precedes the line number. When the -M option causes a pattern to match more than one line, only the first is preceded by its line number. This option is forced if --line-offsets is used.
--no-jit
If the PCRE2 library is built with support for just-in-time compiling (which speeds up matching), pcre2grep automatically makes use of this, unless it was explicitly disabled at build time. This option can be used to disable the use of JIT at run time. It is provided for testing and working round problems. It should never be needed in normal use.
-o, --only-matching
Show only the part of the line that matched a pattern instead of the whole line. 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. If the matched portion of the line is empty, nothing is output unless the file name or line number are being printed, in which case they are shown on an otherwise empty line. This option is mutually exclusive with --file-offsets and --line-offsets.
-onumber, --only-matching=number
Show only the part of the line that matched the capturing parentheses of the given number. Up to 32 capturing parentheses are supported, and -o0 is equivalent to -o without a number. Because these options can be given without an argument (see above), if an argument is present, it must be given in the same shell item, for example, -o3 or --only-matching=2. The comments given for the non-argument case above also apply to this case. If the specified capturing parentheses do not exist in the pattern, or were not set in the match, nothing is output unless the file name or line number are being output.

If this option is given multiple times, multiple substrings are output, in the order the options are given. For example, -o3 -o1 -o3 causes the substrings matched by capturing parentheses 3 and 1 and then 3 again to be output. By default, there is no separator (but see the next option).
--om-separator=text
Specify a separating string for multiple occurrences of -o. The default is an empty string. Separating strings are never coloured.
-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".
--recursion-limit=number
See --match-limit above.
-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 PCRE2 has been compiled with UTF-8 support. All patterns (including those for any --exclude and --include options) and all subject lines that are scanned must be valid strings of UTF-8 characters.
-V, --version
Write the version numbers of pcre2grep and the PCRE2 library to the standard output and then exit. Anything else on the command line is ignored.
-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. This option applies only to the patterns that are matched against the contents of files; it does not apply to patterns specified by any of the --include or --exclude options.
-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 top-level branch in every pattern. This option applies only to the patterns that are matched against the contents of files; it does not apply to patterns specified by any of the --include or --exclude options.

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 PCRE2 library's default (usually the "C" locale) is used.

Newlines

The -N (--newline) option allows pcre2grep to scan files with different newline conventions from the default. Any parts of the input files that are written to the standard output are copied identically, with whatever newline sequences they have in the input. However, the setting of this option does not affect the interpretation of files specified by the -f, --exclude-from, or --include-from options, which are assumed to use the operating system's standard newline sequence, nor does it affect the way in which pcre2grep writes informational messages to the standard error and output streams. For these it uses the string "\n" to indicate newlines, relying on the C I/O library to convert this to an appropriate sequence.

Options Compatibility

Many of the short and long forms of pcre2grep'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 (PCRE2 terminology). However, the --file-list, --file-offsets, --include-dir, --line-offsets, --locale, --match-limit, -M, --multiline, -N, --newline, --om-separator, --recursion-limit, -u, and --utf-8 options are specific to pcre2grep, as is the use of the --only-matching option with a capturing parentheses number.

Although most of the common options work the same way, a few are different in pcre2grep. For example, the --include option's argument is a glob for GNU grep, but a regular expression for pcre2grep. If both the -c and -l options are given, GNU grep lists only file names, without counts, but pcre2grep gives the counts as well.

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 (with one exception) in the next command line item. For example:

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

The exception is the -o option, which may appear with or without data. Because of this, if data is present, it must follow immediately in the same item, for example -o3.

If a long form option is used, the data may appear in the same command line item, separated by an equals character, or (with two exceptions) 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 exceptions to the above are the --colour (or --color) and --only-matching options, for which the data is optional. If one of these options does have data, it must be given in the first form, using an equals character. Otherwise pcre2grep will assume that it has no data.

Calling External Scripts

On non-Windows systems, pcre2grep has, by default, support for calling external programs or scripts during matching by making use of PCRE2's callout facility. However, this support can be disabled when pcre2grep is built. You can find out whether your binary has support for callouts by running it with the --help option. If the support is not enabled, all callouts in patterns are ignored by pcre2grep.

A callout in a PCRE2 pattern is of the form (?C<arg>) where the argument is either a number or a quoted string (see the pcre2callout documentation for details). Numbered callouts are ignored by pcre2grep. String arguments are parsed as a list of substrings separated by pipe (vertical bar) characters. The first substring must be an executable name, with the following substrings specifying arguments:

executable_name|arg1|arg2|...

Any substring (including the executable name) may contain escape sequences started by a dollar character: $<digits> or ${<digits>} is replaced by the captured substring of the given decimal number, which must be greater than zero. If the number is greater than the number of capturing substrings, or if the capture is unset, the replacement is empty.

Any other character is substituted by itself. In particular, $$ is replaced by a single dollar and $| is replaced by a pipe character. Here is an example:

echo -e "abcde\n12345" | pcre2grep \
'(?x)(.)(..(.))
(?C"/bin/echo|Arg1: [$1] [$2] [$3]|Arg2: $|${1}$| ($4)")()' -

Output:

Arg1: [a] [bcd] [d] Arg2: |a| ()
abcde
Arg1: [1] [234] [4] Arg2: |1| ()
12345

The parameters for the execv() system call that is used to run the program or script are zero-terminated strings. This means that binary zero characters in the callout argument will cause premature termination of their substrings, and therefore should not be present. Any syntax errors in the string (for example, a dollar not followed by another character) cause the callout to be ignored. If running the program fails for any reason (including the non-existence of the executable), a local matching failure occurs and the matcher backtracks in the normal way.

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 PCRE2 matching function has a resource limit that causes it to abort in these circumstances. If this happens, pcre2grep outputs an error message and the line that caused the problem to the standard error stream. If there are more than 20 such errors, pcre2grep gives up.

The --match-limit option of pcre2grep can be used to set the overall resource limit; there is a second option called --recursion-limit that sets a limit on the amount of memory (usually stack) that is used (see the discussion of these options above).

Diagnostics

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

See Also

pcre2pattern(3), pcre2syntax(3), pcre2callout(3).

Author

Philip Hazel
University Computing Service
Cambridge, England.

Revision

Last updated: 19 June 2016
Copyright (c) 1997-2016 University of Cambridge.

Info

19 June 2016 PCRE2 10.22