So what?

No, seriously. *Something* has to copy the whole file at some point. I don't know of any mechanism that can avoid that without mucking about with inodes. I personally would only do that as a lark and I wouldn't recommend it as a serious solution to anyone asking this question.

Tie::File is well-maintained, has a nice interface, and is dead-simple to explain. If the original poster starts getting 86400 new messages per day (one hit per second), I'd start worrying about scalability.

I'm okay with "wasting" a few dozen milliseconds and kilobytes here and there if it makes my life easier. If that's unreasonable, so be it.