If you show your actual Perl code (inside "code" tags), you should receive detailed answers. Also provide more information on how it "does not work". Show any warning or error messages, expected output and actual output.

Since you have three hashes, I would think you would want three separate loops, unless you are comparing a values to b and c values.

You may also consider reorganizing your data to be in a single hash-of-arrays structure, since your 3 hashes have identical keys. You would still need the same looping for your comparisons, but a single structure would guarantee coherence, and the relationship amongst your data sets would be more apparent.