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       strict - Perl pragma to restrict unsafe constructs


           use strict;

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

           use strict;
           no strict "vars";


       The "strict" pragma disables certain Perl expressions that could behave unexpectedly or
       are difficult to debug, turning them into errors. The effect of this pragma is limited to
       the current file or scope block.

       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 was neither
             explicitly declared (using any of "my", "our", "state", or "use vars") nor 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,
             "our" in perlfunc, "state" in perlfunc, "local" in perlfunc, and vars.

                 use strict 'vars';
                 $X::foo = 1;         # ok, fully qualified
                 my $foo = 10;        # ok, my() var
                 local $baz = 9;      # blows up, $baz not declared before

                 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 "=>"

                 use strict 'subs';
                 $SIG{PIPE} = Plumber;   # blows up
                 $SIG{PIPE} = "Plumber"; # 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) '...'

       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.