My fellow monk has already provided a good perl solution. I just want to add that if you're on a unix box, your problem can be solved with a couple unix commands. 
cut -f3 -d| X | sort > outx.txt; cut -f3 -d| Y | sort > outy.txt;
comm outx.txt outy.txt;

[download]

Fair warning, I haven't tested these lines. There may be syntax typos. If there are, just read the man pages for cut, sort, and comm. Enjoy.

UPDATE: Simon provides a much more encompassing answer with unix solutions.

In reply to Re: file delta detection by fidesachates
in thread file delta detection by Anonymous Monk

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