i would do something like this, where %a and %b are the hashes to compare:

foreach (sort keys %{{%a, %b}}) {
    if (!exists($b{$_})) { print "$_ only in a\n" }
    elsif (!exists($a{$_})) { print "$_ only in b\n" }
    elsif  ($a{$_} ne $b{$_}) { print "$_: values in a and b differ\n"
+ }
}
[download]

sc