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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 stric-

ture.

"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 sui-

cide problems and subtle dynamic scoping issues, a merely local() variable isn't 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 $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 sub-

routine, unless it is a simple identifier (no colons) and that it

appears in curly braces or on the left hand side of the "=>" sym-

bol.

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.