I have tried iterating with foreach and the hash itself

foreach (keys $hash){
    print $_ . "\n";
}

So far so good ...

Given the code you OPed, it's hard to imagine this would have done anything "good" unless  $hash.was actually a hash reference. If this was the case, please be aware of this from the latest Perl documentation:

Starting with Perl 5.14, an experimental feature allowed keys to take a scalar expression. This experiment has been deemed unsuccessful, and was removed as of Perl 5.24.

This experimental ex-feature was also associated with values, each, push, pop and friends.