NAME
Perl::Critic::Policy::RegularExpressions::PreventUselessMetacharacterEscapes - \Q...\E is for the variable you are interpolating, not for the text around it.
VERSION
version 1.000
Perl::Critic::Policy::RegularExpressions::PreventUselessMetacharacterEscapes
\Q...\E exists to make an interpolated value literal, because you do not know what is in it. You do know what is in the text you typed around it, so escaping that is work the pattern does not need:
qr/\Qowner => "root:$admin"\E/; # the whole thing quotemeta'd
qr/owner => "root:\Q$admin\E"/; # only the part you cannot seeWhy it is worth a policy
The wide form does not merely add noise. Everything inside \Q...\E is still interpolated first, so a sigil in that literal text is a variable:
my $re = qr/\Qowner => "root:$admin"\E/;Under strict that is a compile error naming a variable you never meant to write. Without it, $admin interpolates to empty and you get
(?^:owner\ \=\>\ \"root\:\")-- a pattern that has silently lost everything after the sigil and will not match what you wrote it for.
The escapes it does produce are useless in their own right: \: and \; are not metacharacters, and \. is a thing you can type.
PROHIBITED
qr/\Qfoo.bar\E/; # nothing interpolated: escape the dot yourself
qr/\Qx:$a;\E/; # literals either side of the variable
qr/\Q$a.$b\E/; # a literal between two variables
m/\Qowner => "root:$admin"\E/;
s/\Qfoo.bar\E/baz/;ALLOWED
\Q...\E around interpolation and nothing else, however many:
qr/\Q$a\E/;
qr/\Q$a$b\E/; # adjacent, with no literal between them
qr/owner => "root:\Q$admin\E"/;
qr/\Q$user\E and \Q$host\E/;
qr/\Q$hash{key}\E and \Q$obj->{name}\E/;
qr/\Q@list\E/;CONFIGURATION
allow_whitespace-
Whether literal whitespace inside
\Q...\Eis allowed. Off by default: a space needs no escaping either, and\Q$first \E$secondis usually a span that should have stopped one character earlier.[RegularExpressions::PreventUselessMetacharacterEscapes] allow_whitespace = 1
CAVEATS
\Q...\E works in a double-quoted string as well, with the same hazard. This policy looks only at regexes, which is what its namespace says it does.
A \Q with no \E runs to the end of the pattern, and is read that way here.
METHODS
supported_parameters
allow_whitespace, whether literal whitespace inside a span is tolerated.
default_severity
SEVERITY_MEDIUM. The silent-truncation case is a wrong pattern rather than an untidy one.
default_themes
bugs, maintenance
applies_to
PPI::Token::Regexp::Match, PPI::Token::Regexp::Substitute, PPI::Token::QuoteLike::Regexp
violates
Standard Perl::Critic::Policy interface. One violation per token, however many spans in it are too wide: the fix is the same edit in each.
BUGS
Please report any bugs or feature requests on the bugtracker website https://github.com/Troglodyne-Internet-Widgets/perl-critic-policy-preventuselessmetacharacterescapes/issues
When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.
AUTHORS
Current Maintainers:
George S. Baugh <george@troglodyne.net>
COPYRIGHT AND LICENSE
Copyright (c) 2026 Troglodyne LLC
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.