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strict(3pm)                           Perl Programmers Reference Guide                           strict(3pm)



NAME
       strict - Perl pragma to restrict unsafe constructs

SYNOPSIS
           use strict;

           use strict "vars";
           use strict "refs";
           use strict "subs";

           use strict;
           no strict "vars";

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:  "subs", "vars", and "refs".

       "strict refs"
             This generates a runtime error if you use symbolic references (see perlref).

                 use strict 'refs';
                 $ref = \$foo;
                 print $$ref;        # ok
                 $ref = "foo";
                 print $$ref;        # runtime error; normally ok
                 $file = "STDOUT";
                 print $file "Hi!";  # error; note: no comma after $file

             There is one exception to this rule:

                 $bar = \&{'foo'};
                 &$bar;

             is allowed so that "goto &$AUTOLOAD" would not break under stricture.

       "strict vars"
             This generates a compile-time error if you access a variable that wasn't declared via "our" or
             "use vars", localized via "my()", or wasn't fully qualified.  Because this is to avoid variable
             suicide problems and subtle dynamic scoping issues, a merely local() variable isn't good
             enough.  See "my" in perlfunc and "local" in perlfunc.

                 use strict 'vars';
                 $X::foo = 1;         # ok, fully qualified
                 my $foo = 10;        # ok, my() var
                 local $foo = 9;      # blows up

                 package Cinna;
                 our $bar;                   # Declares $bar in current package
                 $bar = 'HgS';               # ok, global declared via pragma

             The local() generated a compile-time error because you just touched a global name without fully
             qualifying it.

             Because of their special use by sort(), the variables $a and $b are exempted from this check.

       "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 is a simple identifier (no colons) and
             that it appears in curly braces or on the left hand side of the "=>" symbol.

                 use strict 'subs';
                 $SIG{PIPE} = Plumber;       # blows up
                 $SIG{PIPE} = "Plumber";     # just fine: quoted string is always ok
                 $SIG{PIPE} = \&Plumber;     # preferred form

       See "Pragmatic Modules" in perlmodlib.

HISTORY
       "strict 'subs'", with Perl 5.6.1, erroneously permitted to use an unquoted compound identifier (e.g.
       "Foo::Bar") as a hash key (before "=>" or inside curlies), but without forcing it always to a literal
       string.

       Starting with Perl 5.8.1 strict is strict about its restrictions: if unknown restrictions are used,
       the strict pragma will abort with

           Unknown 'strict' tag(s) '...'

       As of version 1.04 (Perl 5.10), strict verifies that it is used as "strict" to avoid the dreaded
       Strict trap on case insensitive file systems.



perl v5.10.0                                     2007-12-18                                      strict(3pm)