in reply to Separate duplicate and unique records

Of course, there's no need to write a whole program, compute expensive hashes and us gobs of memory for things that you can do with a nice, easy to remember one-liner :) 

perl -ne"print{$*ne$_&&$*ne$@?STDOUT:STDERR}$*if$*;($@,$*)=($*,$_);END
+{print{$*ne$_&&$*ne$@?STDOUT:STDERR}$*}" in 1>uniq 2>dups

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Caveat: Usually OS quoting rule changes.

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller
If I understand your problem, I can solve it! Of course, the same can be said for you.

In Section Seekers of Perl Wisdom