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strict(3perl) Perl Programmers Reference Guide strict(3perl)
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"; # 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 v5.20.2 2014-12-27 strict(3perl)
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