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.\" ========================================================================
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.\" ========================================================================
.\"
.IX Title "strict 3"
.TH strict 3 "2002-11-24" "perl v5.8.0" "Perl Programmers Reference Guide"
.SH "NAME"
strict \- Perl pragma to restrict unsafe constructs
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use strict;
.Ve
.PP
.Vb 3
\&    use strict "vars";
\&    use strict "refs";
\&    use strict "subs";
.Ve
.PP
.Vb 2
\&    use strict;
\&    no strict "vars";
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
If no import list is supplied, all possible restrictions are assumed.
(This is the safest mode to operate in, but is sometimes too strict for
casual programming.)  Currently, there are three possible things to be
strict about:  \*(L"subs\*(R", \*(L"vars\*(R", and \*(L"refs\*(R".
.ie n .IP """strict refs""" 6
.el .IP "\f(CWstrict refs\fR" 6
.IX Item "strict refs"
This generates a runtime error if you 
use symbolic references (see perlref).
.Sp
.Vb 7
\&    use strict 'refs';
\&    $ref = \e$foo;
\&    print $$ref;        # ok
\&    $ref = "foo";
\&    print $$ref;        # runtime error; normally ok
\&    $file = "STDOUT";
\&    print $file "Hi!";  # error; note: no comma after $file
.Ve
.Sp
There is one exception to this rule:
.Sp
.Vb 2
\&    $bar = \e&{'foo'};
\&    &$bar;
.Ve
.Sp
is allowed so that \f(CW\*(C`goto &$AUTOLOAD\*(C'\fR would not break under stricture.
.ie n .IP """strict vars""" 6
.el .IP "\f(CWstrict vars\fR" 6
.IX Item "strict vars"
This generates a compile-time error if you access a variable that wasn't
declared via \*(L"our\*(R" or \f(CW\*(C`use vars\*(C'\fR,
localized via \f(CW\*(C`my()\*(C'\fR, or wasn't fully qualified.  Because this is to avoid
variable suicide problems and subtle dynamic scoping issues, a merely
\&\fIlocal()\fR variable isn't good enough.  See \*(L"my\*(R" in perlfunc and
\&\*(L"local\*(R" in perlfunc.
.Sp
.Vb 4
\&    use strict 'vars';
\&    $X::foo = 1;         # ok, fully qualified
\&    my $foo = 10;        # ok, my() var
\&    local $foo = 9;      # blows up
.Ve
.Sp
.Vb 3
\&    package Cinna;
\&    our $bar;                   # Declares $bar in current package
\&    $bar = 'HgS';               # ok, global declared via pragma
.Ve
.Sp
The \fIlocal()\fR generated a compile-time error because you just touched a global
name without fully qualifying it.
.Sp
Because of their special use by \fIsort()\fR, the variables \f(CW$a\fR and \f(CW$b\fR are
exempted from this check.
.ie n .IP """strict subs""" 6
.el .IP "\f(CWstrict subs\fR" 6
.IX Item "strict subs"
This disables the poetry optimization, generating a compile-time error if
you try to use a bareword identifier that's not a subroutine, unless it
appears in curly braces or on the left hand side of the "=>" symbol.
.Sp
.Vb 4
\&    use strict 'subs';
\&    $SIG{PIPE} = Plumber;       # blows up
\&    $SIG{PIPE} = "Plumber";     # just fine: bareword in curlies always ok
\&    $SIG{PIPE} = \e&Plumber;     # preferred form
.Ve
.PP
See \*(L"Pragmatic Modules\*(R" in perlmodlib.