You have described the *nix comm utility, which requires your 2 input files to first be sorted using sort.

For a Perl solution, searching through Categorized Questions and Answers, it seems the answers to How do I compare the lines in two text file? may be helpful, particularly Algorithm::Diff.

In reply to Re: Diff 2 files and print output to file by toolic
in thread Diff 2 files and print output to file by Anonymous Monk

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