the cksum(or checksum)utility in Unix which does a bit-by-bit comparison of files and gives out a number, which is never differrent if there are the slightest changes in the files

Well, this is not exactly what cksum does. It doesn't do any comparing of files. It calculates a number based on the input file and it is very unlikely - but not impossible - that this number is the same for a file and a slightly changed version of that file.

Concerning any perl implementations, search at http://search.cpan.org for Checksum or Digest and you will find plenty of solutions.

-- Hofmator