Re. your map solution, I think it might be safer to test for the existence of a key in case the value is 0 or the empty string. Also grep could come into play.

print
   map  { qq{$_ matches. It's values are $csahash{$_} and $cathhash{$_
+}\n} }
   grep { exists $cathhash{$_} }
   keys %csahash;
[download]

I hope this is of interest.

Cheers,

JohnGG