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Perl::Critic::Policy::ValuesAndExpressions::RequireInterpolationOfMetachars - Warns that you might have used single quotes when you really wanted double-quotes.


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


This policy warns you if you use single-quotes or q// with a string that has unescaped metacharacters that may need interpolation. Its hard to know for sure if a string really should be interpolated without looking into the symbol table. This policy just makes an educated guess by looking for metacharacters and sigils which usually indicate that the string should be interpolated.


  • Variable names to use vars:

        use vars '$x';          # ok
        use vars ('$y', '$z');  # ok
        use vars qw< $a $b >;   # ok
  • Things that look like e-mail addresses:

        print '';           # ok
        $address = '';  # ok


The rcs_keywords option allows you to stop this policy from complaining about things that look like RCS variables, for example, in deriving values for $VERSION variables.

For example, if you've got code like

    our ($VERSION) = (q<$Revision$> =~ m/(\d+)/mx);

You can specify

    rcs_keywords = Revision

in your .perlcriticrc to provide an exemption.


Perl's own warnings pragma also warns you about this.




Jeffrey Ryan Thalhammer <>


Copyright (c) 2005-2011 Imaginative Software Systems. All 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.