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.IX Title "Perl::Critic::Policy::RegularExpressions::ProhibitFixedStringMatches 3pm"
.TH Perl::Critic::Policy::RegularExpressions::ProhibitFixedStringMatches 3pm 2023-07-26 "perl v5.38.0" "User Contributed Perl Documentation"
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.SH NAME
Perl::Critic::Policy::RegularExpressions::ProhibitFixedStringMatches \- Use "eq" or hash instead of fixed\-pattern regexps.
.SH AFFILIATION
.IX Header "AFFILIATION"
This Policy is part of the core Perl::Critic
distribution.
.SH DESCRIPTION
.IX Header "DESCRIPTION"
A regular expression that matches just a fixed set of constant strings
is wasteful of performance and is hard on maintainers.  It is much
more readable and often faster to use \f(CW\*(C`eq\*(C'\fR or a hash to match such
strings.
.PP
.Vb 2
\&    # Bad
\&    my $is_file_function = $token =~ m/\eA (?: open | close | read ) \ez/xms;
\&
\&    # Faster and more readable
\&    my $is_file_function = $token eq \*(Aqopen\*(Aq ||
\&                           $token eq \*(Aqclose\*(Aq ||
\&                           $token eq \*(Aqread\*(Aq;
.Ve
.PP
For larger numbers of strings, a hash is superior:
.PP
.Vb 4
\&    # Bad
\&    my $is_perl_keyword =
\&        $token =~ m/\eA (?: chomp | chop | chr | crypt | hex | index
\&                           lc | lcfirst | length | oct | ord | ... ) \ez/xms;
\&
\&    # Better
\&    Readonly::Hash my %PERL_KEYWORDS => map {$_ => 1} qw(
\&        chomp chop chr crypt hex index lc lcfirst length oct ord ...
\&    );
\&    my $is_perl_keyword = $PERL_KEYWORD{$token};
.Ve
.PP
Conway also suggests using \f(CWlc()\fR instead of a case-insensitive match.
.SS VARIANTS
.IX Subsection "VARIANTS"
This policy detects both grouped and non-grouped strings.  The
grouping may or may not be capturing.  The grouped body may or may not
be alternating.  \f(CW\*(C`\eA\*(C'\fR and \f(CW\*(C`\ez\*(C'\fR are always considered anchoring which
\&\f(CW\*(C`^\*(C'\fR and \f(CW\*(C`$\*(C'\fR are considered anchoring is the \f(CW\*(C`m\*(C'\fR regexp option is
not in use.  Thus, all of these are violations:
.PP
.Vb 7
\&    m/^foo$/;
\&    m/\eA foo \ez/x;
\&    m/\eA foo \ez/xm;
\&    m/\eA(foo)\ez/;
\&    m/\eA(?:foo)\ez/;
\&    m/\eA(foo|bar)\ez/;
\&    m/\eA(?:foo|bar)\ez/;
.Ve
.PP
Furthermore, this policy detects violations in \f(CW\*(C`m//\*(C'\fR, \f(CW\*(C`s///\*(C'\fR and
\&\f(CW\*(C`qr//\*(C'\fR constructs, as you would expect.
.SH CONFIGURATION
.IX Header "CONFIGURATION"
This Policy is not configurable except for the standard options.
.SH CREDITS
.IX Header "CREDITS"
Initial development of this policy was supported by a grant from the
Perl Foundation.
.SH AUTHOR
.IX Header "AUTHOR"
Chris Dolan <cdolan@cpan.org>
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright (c) 2007\-2011 Chris Dolan.  Many rights reserved.
.PP
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