trunk/doc/pcregrep.1

.TH PCREGREP 1
.SH NAME
pcregrep - a grep with Perl-compatible regular expressions.
.SH SYNOPSIS
.B pcregrep [options] [long options] [pattern] [path1 path2 ...]
.
.SH DESCRIPTION
.rs
.sp
\fBpcregrep\fP 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
.\" HREF
\fBpcrepattern\fP(3)
.\"
for a full description of syntax and semantics of the regular expressions
that PCRE supports.
.P
Patterns, whether supplied on the command line or in a separate file, are given
without delimiters. For example:
.sp
  pcregrep 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 they 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, \fBpcregrep\fP reads the standard input. The
standard input can also be referenced by a name consisting of a single hyphen.
For example:
.sp
  pcregrep some-pattern /file1 - /file3
.sp
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 \fBpcregrep\fP behaves. In particular, the \fB-M\fP option makes it
possible to search for patterns 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 \fBpcregrep\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 are limited to 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 (or fails to match when \fB-v\fP is
used), 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 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.
.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,
\fBpcregrep\fP uses the value to set a locale when calling the PCRE library.
The \fB--locale\fP option can be used to override this.
.
.
.SH "SUPPORT FOR COMPRESSED FILES"
.rs
.sp
It is possible to compile \fBpcregrep\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 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. 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 filenames 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 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 \fInumber\fP is expected to be relatively small. However, \fBpcregrep\fP
guarantees to have up to 8K of following text available for context output.
.TP
\fB-B\fP \fInumber\fP, \fB--before-context=\fP\fInumber\fP
Output \fInumber\fP 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 \fInumber\fP is expected to be relatively small. However, \fBpcregrep\fP
guarantees to have up to 8K of preceding text available for context output.
.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 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
\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 \fBpcregrep\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
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.
.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), "recurse" (equivalent to the \fB-r\fP
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.
.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 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 \fB-v\fP is used). If \fB-f\fP is used with \fB-e\fP, 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
\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, \fBpcregrep\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
really matters only if you are using \fB-o\fP to show the part(s) of the line
that matched.
.TP
\fB--exclude\fP=\fIpattern\fP
When \fBpcregrep\fP is searching the files in a directory as a consequence of
the \fB-r\fP (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 \fB--exclude-dir\fP and
\fB--include_dir\fP 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 \fB--include\fP and \fB--exclude\fP, it is excluded.
There is no short form for this option.
.TP
\fB--exclude-dir\fP=\fIpattern\fP
When \fBpcregrep\fP is searching the contents of a directory as a consequence
of the \fB-r\fP (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 \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 pattern as a list of fixed strings, separated by newlines,
instead of as a regular expression. 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).
.TP
\fB-f\fP \fIfilename\fP, \fB--file=\fP\fIfilename\fP
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 \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 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 \fB-e\fP above.
.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 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.
.TP
\fB-h\fP, \fB--no-filename\fP
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.
.TP
\fB--help\fP
Output a help message, giving brief details of the command options and file
type support, and then exit.
.TP
\fB-i\fP, \fB--ignore-case\fP
Ignore upper/lower case distinctions during comparisons.
.TP
\fB--include\fP=\fIpattern\fP
When \fBpcregrep\fP is searching the files in a directory as a consequence of
the \fB-r\fP (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 \fB--exclude-dir\fP
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 \fB--include\fP and \fB--exclude\fP, it is excluded. There is no short
form for this option.
.TP
\fB--include-dir\fP=\fIpattern\fP
When \fBpcregrep\fP is searching the contents of a directory as a consequence
of the \fB-r\fP (recursive search) option, only those subdirectories whose
names match the pattern are included. (Note that the \fB--include\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 \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 \fBpcregrep\fP 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
\fBpcregrep\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 PCRE 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 \fBpcre_exec()\fP function that is called by \fBpcregrep\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, PCRE 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 PCRE 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 last of which is the one 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 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 \fBpcregrep\fP buffers the input file as it scans it. However,
\fBpcregrep\fP 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.)
.TP
\fB-N\fP \fInewline-type\fP, \fB--newline\fP=\fInewline-type\fP
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
(form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and
PS (paragraph separator, U+2029).
.sp
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, \fBpcregrep\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 \fBpcregrep\fP 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,
\fBpcregrep\fP may behave in strange ways.
.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 filename is also being
output, it precedes the line number. This option is forced if
\fB--line-offsets\fP is used.
.TP
\fB--no-jit\fP
If the PCRE library is built with support for just-in-time compiling (which 
speeds up matching), \fBpcregrep\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. 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 printed.
.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 PCRE has been compiled
with UTF-8 support. Both patterns and subject lines must be valid strings of
UTF-8 characters.
.TP
\fB-V\fP, \fB--version\fP
Write the version numbers of \fBpcregrep\fP and the PCRE library that is being
used to the standard error stream.
.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.
.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 branch in every pattern.
.
.
.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 PCRE library's default
(usually the "C" locale) is used.
.
.
.SH "NEWLINES"
.rs
.sp
The \fB-N\fP (\fB--newline\fP) option allows \fBpcregrep\fP to scan files with
different newline conventions from the default. However, the setting of this
option does not affect the way in which \fBpcregrep\fP writes information to
the standard error and output streams. It uses the string "\en" in C
\fBprintf()\fP 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.
.
.
.SH "OPTIONS COMPATIBILITY"
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Many of the short and long forms of \fBpcregrep\fP's options are the same
as in the GNU \fBgrep\fP program (version 2.5.4). Any long option of the form
\fB--xxx-regexp\fP (GNU terminology) is also available as \fB--xxx-regex\fP
(PCRE terminology). However, the \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--recursion-limit\fP,
\fB-u\fP, and \fB--utf-8\fP options are specific to \fBpcregrep\fP, as is the
use of the \fB--only-matching\fP option with a capturing parentheses number.
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Although most of the common options work the same way, a few are different in
\fBpcregrep\fP. For example, the \fB--include\fP option's argument is a glob
for GNU \fBgrep\fP, but a regular expression for \fBpcregrep\fP. If both the
\fB-c\fP and \fB-l\fP options are given, GNU grep lists only file names,
without counts, but \fBpcregrep\fP gives the counts.
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.SH "OPTIONS WITH DATA"
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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:
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  -f/some/file
  -f /some/file
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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.
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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:
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  --file=/some/file
  --file /some/file
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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.
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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 \fBpcregrep\fP will assume that it has no data.
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.SH "MATCHING ERRORS"
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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 PCRE matching function has a resource limit that causes it to abort
in these circumstances. If this happens, \fBpcregrep\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, \fBpcregrep\fP gives up.
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The \fB--match-limit\fP option of \fBpcregrep\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).
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.SH DIAGNOSTICS
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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.
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.SH "SEE ALSO"
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\fBpcrepattern\fP(3), \fBpcretest\fP(1).
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.SH AUTHOR
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Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
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.SH REVISION
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Last updated: 06 September 2011
Copyright (c) 1997-2011 University of Cambridge.
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