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.IX Title "Perl::Critic::Policy::ValuesAndExpressions::ProhibitInterpolationOfLiterals 3pm"
.TH Perl::Critic::Policy::ValuesAndExpressions::ProhibitInterpolationOfLiterals 3pm 2023-07-26 "perl v5.38.0" "User Contributed Perl Documentation"
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.SH NAME
Perl::Critic::Policy::ValuesAndExpressions::ProhibitInterpolationOfLiterals \- Always use single quotes for literal strings.
.SH AFFILIATION
.IX Header "AFFILIATION"
This Policy is part of the core Perl::Critic
distribution.
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Don't use double-quotes or \f(CW\*(C`qq//\*(C'\fR if your string doesn't require
interpolation.  This saves the interpreter a bit of work and it lets
the reader know that you really did intend the string to be literal.
.PP
.Vb 4
\&    print "foobar";     #not ok
\&    print \*(Aqfoobar\*(Aq;     #ok
\&    print qq/foobar/;   #not ok
\&    print q/foobar/;    #ok
\&
\&    print "$foobar";    #ok
\&    print "foobar\en";   #ok
\&    print qq/$foobar/;  #ok
\&    print qq/foobar\en/; #ok
\&
\&    print qq{$foobar};  #preferred
\&    print qq{foobar\en}; #preferred
.Ve
.PP
Use of double-quotes might be reasonable if the string contains single
quote (') characters:
.PP
.Vb 1
\&    print "it\*(Aqs me";    # ok, if configuration flag set
.Ve
.SH CONFIGURATION
.IX Header "CONFIGURATION"
The types of quoting styles to exempt from this policy can be
configured via the \f(CW\*(C`allow\*(C'\fR option.  This must be a
whitespace-delimited combination of some or all of the following
styles: \f(CW\*(C`qq{}\*(C'\fR, \f(CWqq()\fR, \f(CW\*(C`qq[]\*(C'\fR, and \f(CW\*(C`qq//\*(C'\fR.
.PP
This is useful because some folks have configured their editor to
apply special syntax highlighting within certain styles of quotes.
For example, you can tweak \f(CW\*(C`vim\*(C'\fR to use SQL highlighting for
everything that appears within \f(CW\*(C`qq{}\*(C'\fR or \f(CW\*(C`qq[]\*(C'\fR quotes.  But if
those strings are literal, Perl::Critic will complain.  To prevent
this, put the following in your \fI.perlcriticrc\fR file:
.PP
.Vb 2
\&    [ValuesAndExpressions::ProhibitInterpolationOfLiterals]
\&    allow = qq{} qq[]
.Ve
.PP
The flag \f(CW\*(C`allow_if_string_contains_single_quote\*(C'\fR permits
double-quoted strings if the string contains a single quote (')
character.  It defaults to off; to turn it on put the following in
your \fI.perlcriticrc\fR file:
.PP
.Vb 2
\&    [ValuesAndExpressions::ProhibitInterpolationOfLiterals]
\&    allow_if_string_contains_single_quote = 1
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Perl::Critic::Policy::ValuesAndExpressions::RequireInterpolationOfMetachars
.SH AUTHOR
.IX Header "AUTHOR"
Jeffrey Ryan Thalhammer <jeff@imaginative\-software.com>
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright (c) 2005\-2021 Imaginative Software Systems.  All 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.