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.IX Title "Perl::Critic::Policy::Variables::ProhibitEvilVariables 3pm"
.TH Perl::Critic::Policy::Variables::ProhibitEvilVariables 3pm "2018-07-27" "perl v5.26.2" "User Contributed Perl Documentation"
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.SH "NAME"
Perl::Critic::Policy::Variables::ProhibitEvilVariables \- Ban variables that aren't blessed by your shop.
.SH "AFFILIATION"
.IX Header "AFFILIATION"
This Policy is part of the core Perl::Critic
distribution.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Use this policy if you wish to prohibit the use of specific variables. These
may be global variables warned against in \f(CW\*(C`perlvar\*(C'\fR, or just variables whose
names you do not like.
.SH "CONFIGURATION"
.IX Header "CONFIGURATION"
The set of prohibited variables is configurable via the \f(CW\*(C`variables\*(C'\fR and
\&\f(CW\*(C`variables_file\*(C'\fR options.
.PP
The value of \f(CW\*(C`variables\*(C'\fR should be a string of space-delimited, fully
qualified variable names and/or regular expressions.  An example of
prohibiting two specific variables in a \fI.perlcriticrc\fR file:
.PP
.Vb 2
\&    [Variables::ProhibitEvilVariables]
\&    variables = $[ $^S $SIG{_\|_DIE_\|_}
.Ve
.PP
If you prohibit an array or hash (e.g. \f(CW@INC\fR), use of elements of the array
or hash will be prohibited as well. If you specify a subscripted variable (e.g.
\&\f(CW$SIG{_\|_DIE_\|_}\fR), only the literal subscript specified will be detected. The
above <.perlcritic> file, for example, will cause \f(CW\*(C`perlcritic (1)\*(C'\fR to detect
\&\f(CW\*(C`$SIG{_\|_DIE_\|_} = \e&foo\*(C'\fR, but not
.PP
.Vb 2
\&    my $foo = \*(Aq_\|_DIE_\|_\*(Aq;
\&    $SIG{$foo} = \e&foo;
.Ve
.PP
Regular expressions are identified by values beginning and ending with
slashes.  Any variable with a name that matches \f(CW\*(C`m/pattern/sm\*(C'\fR will be
forbidden.  For example:
.PP
.Vb 2
\&    [Variables::ProhibitEvilVariables]
\&    variables = /acme/
.Ve
.PP
would cause all variables that match \f(CW\*(C`m/acme/\*(C'\fR to be forbidden.  If
you want a case-blind check, you can use (?i: ... ).  For example
.PP
.Vb 2
\&    [Variables::ProhibitEvilVariables]
\&    variables = /(?i:acme)/
.Ve
.PP
forbids variables that match \f(CW\*(C`m/acme/smi\*(C'\fR.
.PP
In addition, you can override the default message (\*(L"Prohibited variable
\&\*(R"\fIvariable\fR\*(L" used\*(R") with your own, in order to give suggestions for
alternative action.  To do so, put your message in curly braces after
the variable name or regular expression.  Like this:
.PP
.Vb 2
\&    [Variables::ProhibitEvilVariables]
\&    variables = $[ {Found use of $[. Program to base index 0 instead}
.Ve
.PP
If your message contains curly braces, you can enclose it in parentheses,
angle brackets, or square brackets instead.
.PP
Similarly, the \f(CW\*(C`variables_file\*(C'\fR option gives the name of a file
containing specifications for prohibited variables.  Only one variable
specification is allowed per line and comments start with an octothorp
and run to end of line; no curly braces are necessary for delimiting
messages:
.PP
.Vb 1
\&    $[      # Prohibit the "$[" variable and use the default message.
\&
\&    # Prohibit the "$^S" variable and give a replacement message.
\&    $^S     Having to think about $^S in exception handlers is just wrong
\&
\&    # Use a regular expression.
\&    /acme/  No coyotes allowed.
.Ve
.PP
By default, there are no prohibited variables, although I can think of a
few that should be.  See \f(CW\*(C`perldoc perlvar\*(C'\fR for a few suggestions.
.SH "RESTRICTIONS"
.IX Header "RESTRICTIONS"
Variables of the form \f(CW\*(C`${^foo}\*(C'\fR are not recognized by \s-1PPI\s0 as of version
1.206. When \s-1PPI\s0 recognizes these, this policy will Just Work for them too.
.PP
Only direct references to prohibited variables and literal subscripts will be
recognized. For example, if you prohibit $[, the first line in
.PP
.Vb 2
\& my $foo = \e$[;
\& $$foo = 1;
.Ve
.PP
will be flagged as a violation, but not the second, even though the second, in
fact, assigns to $[. Similarly, if you prohibit \f(CW$SIG\fR{_\|_DIE_\|_}, this policy
will not recognize
.PP
.Vb 2
\& my $foo = \*(Aq_\|_DIE_\|_\*(Aq;
\& $SIG{$foo} = sub {warn \*(AqI cannot die!\*(Aq};
.Ve
.PP
as an assignment to \f(CW$SIG\fR{_\|_DIE_\|_}.
.SH "NOTES"
.IX Header "NOTES"
This policy leans heavily on
Perl::Critic::Policy::Modules::ProhibitEvilModules
by Jeffrey Ryan Thalhammer.
.SH "AUTHOR"
.IX Header "AUTHOR"
Thomas R. Wyant, \s-1III\s0 \fIwyant at cpan dot org\fR
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 2009\-2011 Thomas R. Wyant, \s-1III\s0
.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 \s-1LICENSE\s0 file included with this module.