for my $k (keys(%hash1)) {
    next if !exists($hash2{$k});
    my $v = join_values( delete($hash1{$k}), delete($hash2{$k}) );
    print "$k-->$v\n";
}

print("Leftovers in hash 1:\n");
print "$_\n" for keys(%hash1);

print("Leftovers in hash 2:\n");
print "$_\n" for keys(%hash2);