pcre2/doc/pcre2grep.1

.TH PCRE2GREP 1 "06 April 2016" "PCRE2 10.22"
.SH NAME
pcre2grep - a grep with Perl-compatible regular expressions.
.SH SYNOPSIS
.B pcre2grep [options] [long options] [pattern] [path1 path2 ...]
.
.SH DESCRIPTION
.rs
.sp
\fBpcre2grep\fP 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
.\" HREF
\fBpcre2syntax\fP(3)
.\"
for a quick-reference summary of pattern syntax, or
.\" HREF
\fBpcre2pattern\fP(3)
.\"
for a full description of the syntax and semantics of the regular expressions
that PCRE2 supports.
.P
Patterns, whether supplied on the command line or in a separate file, are given
without delimiters. For example:
.sp
  pcre2grep Thursday /etc/motd
.sp
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.
.P
The first argument that follows any option settings is treated as the single
pattern to be matched when neither \fB-e\fP nor \fB-f\fP 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 \fB-e\fP, \fB-f\fP, or an
argument pattern must be provided.
.P
If no files are specified, \fBpcre2grep\fP reads the standard input. The
standard input can also be referenced by a name consisting of a single hyphen.
For example:
.sp
  pcre2grep some-pattern file1 - file3
.sp
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 \fBpcre2grep\fP behaves. In
particular, the \fB-M\fP option makes it possible to search for strings that
span line boundaries. What defines a line boundary is controlled by the
\fB-N\fP (\fB--newline\fP) option.
.P
The amount of memory used for buffering files that are being scanned is
controlled by a parameter that can be set by the \fB--buffer-size\fP option.
The default value for this parameter is specified when \fBpcre2grep\fP 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.
.P
Patterns can be no longer than 8K or BUFSIZ bytes, whichever is the greater.
BUFSIZ is defined in \fB<stdio.h>\fP. When there is more than one pattern
(specified by the use of \fB-e\fP and/or \fB-f\fP), each pattern is applied to
each line in the order in which they are defined, except that all the \fB-e\fP
patterns are tried before the \fB-f\fP patterns.
.P
By default, as soon as one pattern matches a line, no further patterns are
considered. However, if \fB--colour\fP (or \fB--color\fP) is used to colour the
matching substrings, or if \fB--only-matching\fP, \fB--file-offsets\fP, or
\fB--line-offsets\fP 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.
.P
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).
.P
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.
.P
If the \fBLC_ALL\fP or \fBLC_CTYPE\fP environment variable is set,
\fBpcre2grep\fP uses the value to set a locale when calling the PCRE2 library.
The \fB--locale\fP option can be used to override this.
.
.
.SH "SUPPORT FOR COMPRESSED FILES"
.rs
.sp
It is possible to compile \fBpcre2grep\fP so that it uses \fBlibz\fP or
\fBlibbz2\fP to read files whose names end in \fB.gz\fP or \fB.bz2\fP,
respectively. You can find out whether your binary has support for one or both
of these file types by running it with the \fB--help\fP option. If the
appropriate support is not present, files are treated as plain text. The
standard input is always so treated.
.
.
.SH "BINARY FILES"
.rs
.sp
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 \fB--binary-files\fP option
for a means of changing the way binary files are handled.
.
.
.SH OPTIONS
.rs
.sp
The order in which some of the options appear can affect the output. For
example, both the \fB-h\fP and \fB-l\fP 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.
.TP 10
\fB--\fP
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.
.TP
\fB-A\fP \fInumber\fP, \fB--after-context=\fP\fInumber\fP
Output \fInumber\fP 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 \fInumber\fP is expected to be relatively small. However, \fBpcre2grep\fP
guarantees to have up to 8K of following text available for context output.
.TP
\fB-a\fP, \fB--text\fP
Treat binary files as text. This is equivalent to
\fB--binary-files\fP=\fItext\fP.
.TP
\fB-B\fP \fInumber\fP, \fB--before-context=\fP\fInumber\fP
Output \fInumber\fP 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 \fInumber\fP is expected to be relatively small. However, \fBpcre2grep\fP
guarantees to have up to 8K of preceding text available for context output.
.TP
\fB--binary-files=\fP\fIword\fP
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 \fB-a\fP or \fB--text\fP 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
\fB-I\fP 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.
.TP
\fB--buffer-size=\fP\fInumber\fP
Set the parameter that controls how much memory is used for buffering files
that are being scanned.
.TP
\fB-C\fP \fInumber\fP, \fB--context=\fP\fInumber\fP
Output \fInumber\fP lines of context both before and after each matching line.
This is equivalent to setting both \fB-A\fP and \fB-B\fP to the same value.
.TP
\fB-c\fP, \fB--count\fP
Do not output lines from the files that are being scanned; instead output the
number of matches (or non-matches if \fB-v\fP 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 \fB-M\fP (multiline) option is used (without
\fB-v\fP), there may be more suppressed lines than the number of matches.
.sp
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
\fB--files-with-matches\fP option is also used, only those files whose counts
are greater than zero are listed. When \fB-c\fP is used, the \fB-A\fP,
\fB-B\fP, and \fB-C\fP options are ignored.
.TP
\fB--colour\fP, \fB--color\fP
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.
.TP
\fB--colour=\fP\fIvalue\fP, \fB--color=\fP\fIvalue\fP
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 \fBpcre2grep\fP has to search for all possible matches in a line, not
just one, in order to colour them all.
.sp
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.
.TP
\fB-D\fP \fIaction\fP, \fB--devices=\fP\fIaction\fP
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).
.TP
\fB-d\fP \fIaction\fP, \fB--directories=\fP\fIaction\fP
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 \fB-r\fP 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.
.TP
\fB-e\fP \fIpattern\fP, \fB--regex=\fP\fIpattern\fP, \fB--regexp=\fP\fIpattern\fP
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 \fB-e\fP 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.
.sp
If \fB-f\fP is used with \fB-e\fP, 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 \fB-e\fP 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, \fBpcre2grep\fP 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 \fB-o\fP or \fB--colo(u)r\fP to show the part(s)
of the line that matched.
.TP
\fB--exclude\fP=\fIpattern\fP
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 \fB--file-list\fP, 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 \fB-F\fP, \fB-w\fP, and \fB-x\fP 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 \fB--include\fP
and an \fB--exclude\fP pattern, it is excluded. There is no short form for this
option.
.TP
\fB--exclude-from=\fP\fIfilename\fP
Treat each non-empty line of the file as the data for an \fB--exclude\fP
option. What constitutes a newline when reading the file is the operating
system's default. The \fB--newline\fP 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.
.TP
\fB--exclude-dir\fP=\fIpattern\fP
Directories whose names match the pattern are skipped without being processed,
whatever the setting of the \fB--recursive\fP option. This applies to all
directories, whether listed on the command line, obtained from
\fB--file-list\fP, 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 \fB-F\fP, \fB-w\fP, and \fB-x\fP 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 \fB--include-dir\fP
and \fB--exclude-dir\fP, it is excluded. There is no short form for this
option.
.TP
\fB-F\fP, \fB--fixed-strings\fP
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 \fB--newline\fP option. The \fB-w\fP (match
as a word) and \fB-x\fP (match whole line) options can be used with \fB-F\fP.
They apply to each of the fixed strings. A line is selected if any of the fixed
strings are found in it (subject to \fB-w\fP or \fB-x\fP, 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 \fB--include\fP or
\fB--exclude\fP options.
.TP
\fB-f\fP \fIfilename\fP, \fB--file=\fP\fIfilename\fP
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 \fB--newline\fP 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 \fB-e\fP above.
.sp
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 \fB-f\fP is used, patterns
specified on the command line using \fB-e\fP 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.
.TP
\fB--file-list\fP=\fIfilename\fP
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 \fB--file\fP and \fB--file-list\fP 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.
.TP
\fB--file-offsets\fP
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 \fB-A\fP, \fB-B\fP, and \fB-C\fP
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 \fB--line-offsets\fP
and \fB--only-matching\fP.
.TP
\fB-H\fP, \fB--with-filename\fP
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 \fB-M\fP option causes a pattern to match more than one
line, only the first is preceded by the file name.
.TP
\fB-h\fP, \fB--no-filename\fP
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.
.TP
\fB--help\fP
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.
.TP
\fB-I\fP
Ignore binary files. This is equivalent to
\fB--binary-files\fP=\fIwithout-match\fP.
.TP
\fB-i\fP, \fB--ignore-case\fP
Ignore upper/lower case distinctions during comparisons.
.TP
\fB--include\fP=\fIpattern\fP
If any \fB--include\fP patterns are specified, the only files that are
processed are those that match one of the patterns (and do not match an
\fB--exclude\fP pattern). This option does not affect directories, but it
applies to all files, whether listed on the command line, obtained from
\fB--file-list\fP, 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 \fB-F\fP, \fB-w\fP, and \fB-x\fP options do not apply to
this pattern. The option may be given any number of times. If a file name
matches both an \fB--include\fP and an \fB--exclude\fP pattern, it is excluded.
There is no short form for this option.
.TP
\fB--include-from=\fP\fIfilename\fP
Treat each non-empty line of the file as the data for an \fB--include\fP
option. What constitutes a newline for this purpose is the operating system's
default. The \fB--newline\fP option has no effect on this option. This option
may be given any number of times; all the files are read.
.TP
\fB--include-dir\fP=\fIpattern\fP
If any \fB--include-dir\fP patterns are specified, the only directories that
are processed are those that match one of the patterns (and do not match an
\fB--exclude-dir\fP pattern). This applies to all directories, whether listed
on the command line, obtained from \fB--file-list\fP, 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 \fB-F\fP,
\fB-w\fP, and \fB-x\fP options do not apply to this pattern. The option may be
given any number of times. If a directory matches both \fB--include-dir\fP and
\fB--exclude-dir\fP, it is excluded. There is no short form for this option.
.TP
\fB-L\fP, \fB--files-without-match\fP
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.
.TP
\fB-l\fP, \fB--files-with-matches\fP
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 \fB-c\fP (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 \fB-c\fP is a way of suppressing the listing of files with no matches.
.TP
\fB--label\fP=\fIname\fP
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.
.TP
\fB--line-buffered\fP
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 \fBpcre2grep\fP 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
\fBpcre2grep\fP to buffer up large amounts of data. However, its use will
affect performance, and the \fB-M\fP (multiline) option ceases to work.
.TP
\fB--line-offsets\fP
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 \fB-n\fP option), and the
offset and length are separated by a comma. In this mode, no context is shown.
That is, the \fB-A\fP, \fB-B\fP, and \fB-C\fP 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 \fB--file-offsets\fP and \fB--only-matching\fP.
.TP
\fB--locale\fP=\fIlocale-name\fP
This option specifies a locale to be used for pattern matching. It overrides
the value in the \fBLC_ALL\fP or \fBLC_CTYPE\fP 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.
.TP
\fB--match-limit\fP=\fInumber\fP
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 \fBpcre2_match()\fP function that is called by \fBpcre2grep\fP to
do the matching has two parameters that can limit the resources that it uses.
.sp
The \fB--match-limit\fP 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 \fBmatch()\fP which it calls repeatedly (sometimes recursively). The
limit set by \fB--match-limit\fP 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.
.sp
The \fB--recursion-limit\fP option is similar to \fB--match-limit\fP, but
instead of limiting the total number of times that \fBmatch()\fP 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 \fBmatch()\fP are recursive. This limit is
of use only if it is set smaller than \fB--match-limit\fP.
.sp
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.
.TP
\fB-M\fP, \fB--multiline\fP
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.
.sp
When this option is set, the PCRE2 library is called in "multiline" mode.
However, \fBpcre2grep\fP still processes the input line by line. The difference
is that a matched string may extend past the end of a line and continue on
one or more subsequent lines. The newline sequence 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:
.sp
  pcre2grep -M 'regular\es+expression' <file>
.sp
The \es 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.
.sp
There is a limit to the number of lines that can be matched, imposed by the way
that \fBpcre2grep\fP buffers the input file as it scans it. However,
\fBpcre2grep\fP 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 \fB-M\fP option
does not work when input is read line by line (see \fP--line-buffered\fP.)
.TP
\fB-N\fP \fInewline-type\fP, \fB--newline\fP=\fInewline-type\fP
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).
.sp
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, \fBpcre2grep\fP uses the library's default.
The possible values for this option are CR, LF, CRLF, ANYCRLF, or ANY. This
makes it possible to use \fBpcre2grep\fP 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,
\fBpcre2grep\fP may behave in strange ways. Note that this option does not
apply to files specified by the \fB-f\fP, \fB--exclude-from\fP, or
\fB--include-from\fP options, which are expected to use the operating system's
standard newline sequence.
.TP
\fB-n\fP, \fB--line-number\fP
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 \fB-M\fP option causes a
pattern to match more than one line, only the first is preceded by its line
number. This option is forced if \fB--line-offsets\fP is used.
.TP
\fB--no-jit\fP
If the PCRE2 library is built with support for just-in-time compiling (which
speeds up matching), \fBpcre2grep\fP 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.
.TP
\fB-o\fP, \fB--only-matching\fP
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 \fB-A\fP, \fB-B\fP, and
\fB-C\fP options are ignored. If there is more than one match in a line, each
of them is shown separately. If \fB-o\fP is combined with \fB-v\fP (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 \fB--file-offsets\fP and \fB--line-offsets\fP.
.TP
\fB-o\fP\fInumber\fP, \fB--only-matching\fP=\fInumber\fP
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 \fB-o\fP 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.
.sp
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).
.TP
\fB--om-separator\fP=\fItext\fP
Specify a separating string for multiple occurrences of \fB-o\fP. The default
is an empty string. Separating strings are never coloured.
.TP
\fB-q\fP, \fB--quiet\fP
Work quietly, that is, display nothing except error messages. The exit
status indicates whether or not any matches were found.
.TP
\fB-r\fP, \fB--recursive\fP
If any given path is a directory, recursively scan the files it contains,
taking note of any \fB--include\fP and \fB--exclude\fP 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 \fB-d\fP
option to "recurse".
.TP
\fB--recursion-limit\fP=\fInumber\fP
See \fB--match-limit\fP above.
.TP
\fB-s\fP, \fB--no-messages\fP
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.
.TP
\fB-u\fP, \fB--utf-8\fP
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 \fB--exclude\fP and
\fB--include\fP options) and all subject lines that are scanned must be valid
strings of UTF-8 characters.
.TP
\fB-V\fP, \fB--version\fP
Write the version numbers of \fBpcre2grep\fP and the PCRE2 library to the
standard output and then exit. Anything else on the command line is
ignored.
.TP
\fB-v\fP, \fB--invert-match\fP
Invert the sense of the match, so that lines which do \fInot\fP match any of
the patterns are the ones that are found.
.TP
\fB-w\fP, \fB--word-regex\fP, \fB--word-regexp\fP
Force the patterns to match only whole words. This is equivalent to having \eb
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 \fB--include\fP or \fB--exclude\fP options.
.TP
\fB-x\fP, \fB--line-regex\fP, \fB--line-regexp\fP
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 \fB--include\fP or \fB--exclude\fP options.
.
.
.SH "ENVIRONMENT VARIABLES"
.rs
.sp
The environment variables \fBLC_ALL\fP and \fBLC_CTYPE\fP are examined, in that
order, for a locale. The first one that is set is used. This can be overridden
by the \fB--locale\fP option. If no locale is set, the PCRE2 library's default
(usually the "C" locale) is used.
.
.
.SH "NEWLINES"
.rs
.sp
The \fB-N\fP (\fB--newline\fP) option allows \fBpcre2grep\fP 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 \fB-f\fP,
\fB--exclude-from\fP, or \fB--include-from\fP options, which are assumed to use
the operating system's standard newline sequence, nor does it affect the way in
which \fBpcre2grep\fP writes informational messages to the standard error and
output streams. For these it uses the string "\en" to indicate newlines,
relying on the C I/O library to convert this to an appropriate sequence.
.
.
.SH "OPTIONS COMPATIBILITY"
.rs
.sp
Many of the short and long forms of \fBpcre2grep\fP's options are the same
as in the GNU \fBgrep\fP program. Any long option of the form
\fB--xxx-regexp\fP (GNU terminology) is also available as \fB--xxx-regex\fP
(PCRE2 terminology). However, the \fB--file-list\fP, \fB--file-offsets\fP,
\fB--include-dir\fP, \fB--line-offsets\fP, \fB--locale\fP, \fB--match-limit\fP,
\fB-M\fP, \fB--multiline\fP, \fB-N\fP, \fB--newline\fP, \fB--om-separator\fP,
\fB--recursion-limit\fP, \fB-u\fP, and \fB--utf-8\fP options are specific to
\fBpcre2grep\fP, as is the use of the \fB--only-matching\fP option with a
capturing parentheses number.
.P
Although most of the common options work the same way, a few are different in
\fBpcre2grep\fP. For example, the \fB--include\fP option's argument is a glob
for GNU \fBgrep\fP, but a regular expression for \fBpcre2grep\fP. If both the
\fB-c\fP and \fB-l\fP options are given, GNU grep lists only file names,
without counts, but \fBpcre2grep\fP gives the counts as well.
.
.
.SH "OPTIONS WITH DATA"
.rs
.sp
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:
.sp
  -f/some/file
  -f /some/file
.sp
The exception is the \fB-o\fP 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.
.P
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:
.sp
  --file=/some/file
  --file /some/file
.sp
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.
.P
The exceptions to the above are the \fB--colour\fP (or \fB--color\fP) and
\fB--only-matching\fP 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 \fBpcre2grep\fP will assume that it has no data.
.
.
.SH "CALLING EXTERNAL SCRIPTS"
.rs
.sp
On non-Windows systems, \fBpcre2grep\fP 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 \fBpcre2grep\fP is built.
You can find out whether your binary has support for callouts by running it
with the \fB--help\fP option. If the support is not enabled, all callouts in
patterns are ignored by \fBpcre2grep\fP.
.P
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
.\" HREF
\fBpcre2callout\fP
.\"
documentation for details). Numbered callouts are ignored by \fBpcre2grep\fP.
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:
.sp
  executable_name|arg1|arg2|...
.sp
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.
.P
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:
.sp
  echo -e "abcde\en12345" | pcre2grep \e
    '(?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
.sp
The parameters for the \fBexecv()\fP 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.
.
.
.SH "MATCHING ERRORS"
.rs
.sp
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+)*\ed 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, \fBpcre2grep\fP outputs an error
message and the line that caused the problem to the standard error stream. If
there are more than 20 such errors, \fBpcre2grep\fP gives up.
.P
The \fB--match-limit\fP option of \fBpcre2grep\fP can be used to set the
overall resource limit; there is a second option called \fB--recursion-limit\fP
that sets a limit on the amount of memory (usually stack) that is used (see the
discussion of these options above).
.
.
.SH DIAGNOSTICS
.rs
.sp
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
\fB-s\fP option to suppress error messages about inaccessible files does not
affect the return code.
.
.
.SH "SEE ALSO"
.rs
.sp
\fBpcre2pattern\fP(3), \fBpcre2syntax\fP(3), \fBpcre2callout\fP(3).
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 06 April 2016
Copyright (c) 1997-2016 University of Cambridge.
.fi