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