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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";
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 the perlref manpage).
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 the perlfunc manpage and
local in the perlfunc manpage.
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 the perlmodlib manpage.
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
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