pcregrep searches files for character patterns, in the same way
as other grep commands do, but it uses the PCRE regular
expression library to support patterns that are compatible with
the regular expressions of Perl 5. See pcresyntax(3) for a quick-
reference summary of pattern syntax, or pcrepattern(3) for a full
description of the syntax and semantics of the regular
expressions that PCRE supports.
Patterns, whether supplied on the command line or in a separate
file, are given without delimiters. For example:
pcregrep Thursday /etc/motd
If you attempt to use delimiters (for example, by surrounding a
pattern with slashes, as is common in Perl scripts), they are
interpreted as part of the pattern. Quotes can of course be used
to delimit patterns on the command line because they are
interpreted by the shell, and indeed 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, pcregrep reads the standard input. The
standard input can also be referenced by a name consisting of a
single hyphen. For example:
pcregrep some-pattern /file1 - /file3
By default, each line that matches a pattern is copied to the
standard output, and if there is more than one file, the file
name is output at the start of each line, followed by a colon.
However, there are options that can change how pcregrep behaves.
In particular, the -M option makes it possible to search for
patterns that span line boundaries. What defines a line boundary
is controlled by the -N (--newline) option.
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 pcregrep 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, pcregrep
uses the value to set a locale when calling the PCRE library.
The --locale option can be used to override this.
