Perl regular expressions have multiple types of grouping syntax. The basic parentheses (e.g. m/(foo)/) captures into the magic variable $1. Non-capturing groups (e.g. m/(?:foo)/ are useful because they have better runtime performance and do not copy strings to the magic global capture variables.

It's also easier on the maintenance programmer if you consistently use capturing vs. non-capturing groups, because that programmer can tell more easily which regexps can be refactored without breaking surrounding code which may use the captured values.



We use the Regexp::Parser manpage to analyze the regular expression syntax. This is an optional module for Perl::Critic, so it will not be automatically installed by CPAN for you. If you wish to use this policy, you must install that module first.

qr// interpolation

This policy can be confused by interpolation of qr// elements, but those are always false negatives. For example:

    my $foo_re = qr/(foo)/;
    my ($foo) = m/$foo_re (bar)/x;

A human can tell that this should be a violation because there are two captures but only the first capture is used, not the second. The policy only notices that there is one capture in the regexp and remains happy.


Initial development of this policy was supported by a grant from the Perl Foundation.


Chris Dolan <cdolan@cpan.org>


Copyright (c) 2007 Chris Dolan. Many rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module