package Bad;

use warnings;

sub gen_warning {
    print "Undeclared: >>>$x<<<";
}

1;

##</code><code>##

$ perl -le '
    use Bad;

    Bad::gen_warning();
'
Use of uninitialized value $Bad::x in concatenation (.) or string at Bad.pm line 6.
Undeclared: >>><<<

##</code><code>##

$ perl -le '
    use Bad;
    {
        no warnings;   
        Bad::gen_warning();
    }                         
'
Use of uninitialized value $Bad::x in concatenation (.) or string at Bad.pm line 6.
Undeclared: >>><<<

##</code><code>##

$ perl -le '
    use Bad;

    {
        no warnings "redefine";
        sub Bad::gen_warning {
            use warnings "redefine";
            no warnings "uninitialized";
            print "Undeclared: >>>$x<<<";
        }
    }

    Bad::gen_warning();
'
Undeclared: >>><<<