Not that you aksed, but I thought I might mention that mtime as reported by perl's stat() is based on an offset from the local operating system's epoch. The epoch can vary from platform to plaform. That may or may not matter to you, but you should keep it in mind if you decide to start comparing mtimes from system to system.

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Oops... I think perl defines it's own portable epoch, however 'perldoc -f stat' warns about portability of ctime on my plaform. You should check the perldocs for each system just to be safe.