use warnings;

##</code><code>##

use strict;

##</code><code>##

use warnings;
use strict;

my $x;
print "$x\n";

##</code><code>##

Use of uninitialized value $x in concatenation (.) or string at script.pl line 4.

##</code><code>##

use warnings;
use strict;

print "$y\n";

##</code><code>##

Global symbol "$y" requires explicit package name (did you forget to declare "my $y"?) at script.pl line 4.