Perl::Critic::Policy::RegularExpressions::RequireExtendedFormattingExceptForSplit - Always use the /x modifier with regular expressions, except when the regex is used


version 2.05


Extended regular expression formatting allows you mix whitespace and comments into the pattern, thus making them much more readable.

    # Match a single-quoted string efficiently...

    m{'[^\\']*(?:\\.[^\\']*)*'};  #Huh?

    # Same thing with extended format...

        '           # an opening single quote
        [^\\']      # any non-special chars (i.e. not backslash or single quote)
        (?:         # then all of...
            \\ .    #    any explicitly backslashed char
            [^\\']* #    followed by an non-special chars
        )*          # ...repeated zero or more times
        '           # a closing single quote


You might find that putting a /x on short regular expressions to be excessive. An exception can be made for them by setting minimum_regex_length_to_complain_about to the minimum match length you'll allow without a /x. The length only counts the regular expression, not the braces or operators.

    minimum_regex_length_to_complain_about = 5

    $num =~ m<(\d+)>;              # ok, only 5 characters
    $num =~ m<\d\.(\d+)>;          # not ok, 9 characters

This option defaults to 0.

Because using /x on a regex which has whitespace in it can make it harder to read (you have to escape all that innocent whitespace), by default, you can have a regular expression that only contains whitespace and word characters without the modifier. If you want to restrict this, turn on the strict option.

    strict = 1

    $string =~ m/Basset hounds got long ears/;  # no longer ok

This option defaults to false.



Currently only one parameter is supported: minimum_regex_length_to_complain_about.

Regular expressions that are shorter than this number, no violation is thrown.


Default theme is reneeb.


Be default this policy is of medium severity.


By default this policy applies to

  • PPI::Token::Regexp::Match

  • PPI::Token::Regexp::Substitute

  • PPI::Token::QuoteLike::Regexp


For common regular expressions like e-mail addresses, phone numbers, dates, etc., have a look at the Regexp::Common module. Also, be cautions about slapping modifier flags onto existing regular expressions, as they can drastically alter their meaning. See for an interesting discussion on the effects of blindly modifying regular expression flags.


Add an exemption for regular expressions that contain \Q at the beginning and don't use \E until the very end, if at all.


Renee Baecker <>


This software is Copyright (c) 2015 by Renee Baecker.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)