Actually a good tail implementation is more complex than it looks, and still does not need unbuffered IO.

I suggest that you look at IO::Select and see if it does not help you figure out how it works.

ObRandomNote1: You can ask for unbuffered input, but that only unbuffers it from the time you read it. The process writing it to you may (and probably does) use buffering. For tests use Perl scripts that have $| set to 1.

ObRandomNote2: Buffered IO is usually more efficient.