I think prehaps your behavior is caused by buffering of the input, then. Is the problem fixed when you close TO_P (after sending the exit command) or when you send exit\n instead of exit? (Which may be enough to convince perl that it should return from the <FROM_P> which I think it's not doing. But it'd be nice if you'd to have the forked process to print some stuff (to a file or STDERR) so you can tell where its hanging...)