My mind's been a bit muddled lately ;-), and I only have grasped the tip of your iceberg, but it is reminiscent of using FIONREAD. Run perldoc -q filehandle and search for the section under How can I tell whether there's a character waiting on a filehandle? It explains how to use FIONREAD. You can also look at my example of it's use in IPC3 buffer limit problem. I hope it's useful to you.