PerlPerl::Critic::Policy::RegularExpressions::ProhibitEscapedMetacharacters(3)NAMEPerl::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
perlPerl::Critic::Policy::RegularExpressions::ProhibitEscapedMetacharacters(3)
