my %current,%last;

my %keys;

map { $keys{$_}; } keys %current, keys %last;

my %changes = ();

foreach my $k (keys %keys) {
  $changes{$k} = $current{$k} unless
      $current{$k} eq $last{$k};
}

##</code><code>##

my %current,%last,%keys;

foreach my $k (keys %current,keys %last) {
   next unless(exists $current{$k});
   $keys{$k} = 1;
}