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.IX Title "Perl::Critic::Policy::RegularExpressions::ProhibitUselessTopic 3pm"
.TH Perl::Critic::Policy::RegularExpressions::ProhibitUselessTopic 3pm "2020-05-17" "perl v5.30.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
Perl::Critic::Policy::RegularExpressions::ProhibitUselessTopic \- Don't use $_ to match against regexes.
.SH "AFFILIATION"
.IX Header "AFFILIATION"
This Policy is part of the Perl::Critic distribution.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
It is not necessary to specify the topic variable \f(CW$_\fR when matching
against a regular expression.
.PP
Match or substitution operations are performed against variables, such as:
.PP
.Vb 3
\&    $x =~ /foo/;
\&    $x =~ s/foo/bar/;
\&    $x =~ tr/a\-mn\-z/n\-za\-m/;
.Ve
.PP
If a variable is not specified, the match is against \f(CW$_\fR.
.PP
.Vb 3
\&    # These are identical.
\&    /foo/;
\&    $_ =~ /foo/;
\&
\&    # These are identical.
\&    s/foo/bar/;
\&    $_ =~ s/foo/bar/;
\&
\&    # These are identical.
\&    tr/a\-mn\-z/n\-za\-m/;
\&    $_ =~ tr/a\-mn\-z/n\-za\-m/;
.Ve
.PP
This applies to negative matching as well.
.PP
.Vb 3
\&    # These are identical
\&    if ( $_ !~ /DEBUG/ ) { ...
\&    if ( !/DEBUG ) { ...
.Ve
.PP
Including the \f(CW\*(C`$_ =~\*(C'\fR or \f(CW\*(C`$_ !~\*(C'\fR is unnecessary, adds complexity,
and is not idiomatic Perl.
.SH "CONFIGURATION"
.IX Header "CONFIGURATION"
This Policy is not configurable except for the standard options.
.SH "AUTHOR"
.IX Header "AUTHOR"
Andy Lester <andy@petdance.com>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 2013 Andy Lester <andy@petdance.com>
.PP
This library is free software; you can redistribute it and/or modify it
under the terms of the Artistic License 2.0.