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 &$AUTOLOADwould not break under stricture. |
strict vars |
This generates a compile-time error if you access a variable that wasnt
declared via ouror use vars, localized via my(), or wasnt fully qualified. Because this is to avoid variable suicide problems and subtle dynamic scoping issues, a merely local() variable isnt 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 $aand $bare exempted from this check. |
strict subs |
This disables the poetry optimization, generating a compile-time error if
you try to use a bareword identifier thats 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
|
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.