The only mention of this, that I've seen is in "perldoc -q filehandle" , scroll to section " How can I tell whether there's a character waiting on a filehandle?" It describes how to read the amount of bytes to be read on a filehandle, but it is for unix. But maybe its worth a try on Windows, or maybe the ActiveState documentation has some extra docs on how to do this. Their docs are better than the perldocs, for windows.