Perl::Critic::Policy::RegularExpressions::ProhibitCaptureWithoutTest(3)

NAME
Perl::Critic::Policy::RegularExpressions::ProhibitCaptureWithoutTest - Capture variable used outside conditional.

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

DESCRIPTION
If a regexp match fails, then any capture variables ($1, $2, ...) will be unaffected. They will retain whatever old values they may have had. Therefore it's important to check the return value of a match before using those variables.

    '12312123' =~ /(2)/;
    print $1;    # Prints 2
    '123123123' =~ /(X)/;
    print $1;    # Prints 2, because $1 has not changed.

Note that because the values of $1 etc will be unaffected, you cannot determine if a match succeeded by checking to see if the capture variables have values.

    # WRONG
    $str =~ /foo(.+)/;
    if ( $1 ) {
        print "I found $1 after 'foo'";
    }

This policy checks that the previous regexp for which the capture variable is in-scope is either in a conditional or causes an exception or other control transfer (i.e. "next", "last", "redo", "return", or sometimes "goto") if the match fails.

A "goto" is only accepted by this policy if it is a co-routine call (i.e. "goto &foo") or a "goto LABEL" where the label does not fall between the "goto" and the capture variable in the scope of the "goto". A computed "goto" (i.e. something like "goto (qw{foo bar baz})[$i]") is not accepted by this policy because its target can not be statically determined.

This policy does not check whether that conditional is actually testing a regexp result, nor does it check whether a regexp actually has a capture in it. Those checks are too hard.

This policy also does not check arbitrarily complex conditionals guarding regexp results, for pretty much the same reason. Simple things like

 m/(foo)/ or die "No foo!";
 die "No foo!" unless m/(foo)/;

will be handled, but something like

 m/(foo)/ or do {
   ... lots of complicated calculations here ...
   die "No foo!";
 };

are beyond its scope.

CONFIGURATION
By default, this policy considers "die", "croak", and "confess" to throw exceptions. If you have additional subroutines or methods that may be used in lieu of one of these, you can configure them in your perlcriticrc as follows:

 [RegularExpressions::ProhibitCaptureWithoutTest]
 exception_source = my_exception_generator

BUGS
This policy does not recognize named capture variables. Yet.

AUTHOR
Chris Dolan <cdolan@cpan.org>

COPYRIGHT
Copyright (c) 2006-2017 Chris Dolan.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.