strict(3p) Perl Programmers Reference Guide strict(3p)
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 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 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() vari-
able isn't good enough. See "my" in perlfunc and
"local" in perlfunc.
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strict(3p) Perl Programmers Reference Guide strict(3p)
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 iden-
tifier 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.
"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 forc-
ing it always to a literal string.
Starting with Perl 5.8.1 strict is strict about its restric-
tions: if unknown restrictions are used, the strict pragma
will abort with
Unknown 'strict' tag(s) '...'
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