I covered this issue exhaustively at Performing a tail(1) in Perl (reading the last N lines of a file). You might want to look there for OWTDI. I actually took about tail(1) for the PPT project (see KM's response) to rip the guts out into a module, but at the moment the parts are lying around on the floor.

The idea is that the stand-alone tail program just becomes a fairly simple object instantiation, but then you could also use the module in your own programs.