package strict; =head1 NAME strict - Perl pragma to restrict unsafe constructs =head1 SYNOPSIS use strict; use strict "vars"; use strict "refs"; use strict "subs"; use strict; no strict "vars"; =head1 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". =over 6 =item C This generates a runtime error if you use symbolic references (see L). use strict 'refs'; $ref = \$foo; print $$ref; # ok $ref = "foo"; print $$ref; # runtime error; normally ok =item C This generates a compile-time error if you access a variable that wasn't declared via C, localized via C 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 L and L. use strict 'vars'; $X::foo = 1; # ok, fully qualified my $foo = 10; # ok, my() var local $foo = 9; # blows up package Cinna; use vars qw/ $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. =item C 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 appears in curly braces or on the left hand side of the "=E" symbol. use strict 'subs'; $SIG{PIPE} = Plumber; # blows up $SIG{PIPE} = "Plumber"; # just fine: bareword in curlies always ok $SIG{PIPE} = \&Plumber; # preferred form =back See L. =cut $strict::VERSION = "1.01"; my %bitmask = ( refs => 0x00000002, subs => 0x00000200, vars => 0x00000400 ); sub bits { my $bits = 0; foreach my $s (@_){ $bits |= $bitmask{$s} || 0; }; $bits; } sub import { shift; $^H |= bits(@_ ? @_ : qw(refs subs vars)); } sub unimport { shift; $^H &= ~ bits(@_ ? @_ : qw(refs subs vars)); } 1;