osx man page for strict

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 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 "=>"
	     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 v5.16.2							    2012-10-11							       strict(3pm)