<Updated>
I like nuance's idea (above). I now store undef as the value when a key is missing from one hash. See nuance's description above for an explanation of the "return" values.
</Updated>

Here's some punctuation for you:

(This is a short, concentrated way to do it - only 4 lines)

# Keys 7 and 8 are unique, keys 2,4 and 6 have different values
my %R = (1=>1, 2=>2,   3=>3, 4=>4,   5=>5, 6=>6,   7=>7);
my %S = (1=>1, 2=>'b', 3=>3, 4=>'d', 5=>5, 6=>'f', 8=>8);

# 1) Keys in %R which are not in %S
# 2) Keys in %S which are not in %R
# 3) Keys in both which have different values
my %Diffs = ((map(($_ => [$R{$_}, undef]),  grep {not exists $S{$_}} k
+eys %R)),
             (map(($_ => [undef,  $S{$_}]), grep {not exists $R{$_}} k
+eys %S)),
             (map(($_ => [$R{$_}, $S{$_}]),
                  grep {exists $S{$_} and $R{$_} ne $S{$_}}  keys %R))
+);

# Print out what we found
for (sort keys %Diffs){
  print $_, ': ', join(', ', map(defined $_ ? $_ : 'undef', @{$Diffs{$
+_}})), "\n";
}
[download]

A couple points to note:

• if your values are numeric, change the 'ne' in the third Diffs section
• we use an anonymous array ref to store the values in %Diffs, so remember to dereference it when you use %Diffs

Enjoy!

Russ