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

       strict - Perl pragma to restrict unsafe constructs

           use strict;

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

           use strict;
           no strict "vars";

       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'};

             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 prob-
             lems and subtle dynamic scoping issues, a merely local() variable isn't good enough.  See "my" in perl-
             func 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 qualify-
             ing 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 iden-
             tifier 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.

       "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) '...'

perl v5.8.8                       2001-09-21                         strict(3)