NAME

       Perl::Critic::Policy::RegularExpressions::ProhibitEscapedMetacharacters - Use character
       classes for literal meta-characters instead of escapes.

AFFILIATION

       This Policy is part of the core Perl::Critic distribution.

DESCRIPTION

       Ever heard of leaning toothpick syndrome?  That comes from writing regular expressions
       that match on characters that are significant in regular expressions.  For example, the
       expression to match four forward slashes looks like:

           m/\/\/\/\//;

       Well, this policy doesn't solve that problem (write it as "m{////}" instead!) but solves a
       related one.  As seen above, the escapes make the expression hard to parse visually.  One
       solution is to use character classes.  You see, inside of character classes, the only
       characters that are special are "\", "]", "^" and "-", so you don't need to escape the
       others.  So instead of the following loose IPv4 address matcher:

           m/ \d+ \. \d+ \. \d+ \. \d+ /x;

       You could write:

           m/ \d+ [.] \d+ [.] \d+ [.] \d+ /x;

       which is certainly more readable, if less recognizable prior the publication of Perl Best
       Practices.  (Of course, you should really use Regexp::Common::net to match IPv4
       addresses!)

       Specifically, this policy forbids backslashes immediately prior to the following
       characters:

           { } ( ) . * + ? | #

       We make special exception for "$" because "/[$]/" turns into "/[5.008006/" for Perl 5.8.6.
       We also make an exception for "^" because it has special meaning (negation) in a character
       class.  Finally, "[" and "]" are exempt, of course, because they are awkward to represent
       in character classes.

       Note that this policy does not forbid unnecessary escaping.  So go ahead and (pointlessly)
       escape "!" characters.

CONFIGURATION

       This Policy is not configurable except for the standard options.

BUGS

       Perl treats "m/[#]/x" in unexpected ways.  I think it's a bug in Perl itself, but am not
       100% sure that I have not simply misunderstood...

       This part makes sense:

           "#f" =~ m/[#]f/x;     # match
           "#f" =~ m/[#]a/x;     # no match

       This doesn't:

           $qr  = qr/f/;
           "#f" =~ m/[#]$qr/x; # no match

       Neither does this:

           print qr/[#]$qr/x;  # yields '(?x-ism:[#]$qr
                                       )'

CREDITS

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

AUTHOR

       Chris Dolan <cdolan@cpan.org>

COPYRIGHT

       Copyright (c) 2007-2011 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

perl v5.20.2         Perl::Critic::Policy::RegularExpressions::ProhibitEscapedMetacharacters(3pm)