Thanks guys, you are really helping me out here. Now I need to find out the duplicates and merge two data sets for these duplicates while discarding the unmatched ones. I used the following script to find out the duplicates, and it indeed found the common keys.

foreach (do {
    my %matcher;
    @matcher{map lc,keys %hash1}=();
    grep exists $matcher{lc $_},keys %hash2;
  }) {
  print "$_ matches\n";
}
[download]

yet I would like to merge the two data sets, so am I doing totally wrong by bothering with the matches as an extra loop? is there a way to merge two hashes conditional on common keys?