When you reopen INPUT (the '>&' symbols are an error) the original is closed. You need to open two distinct filehandles and use four argument select ('perldoc -f select') to read them simultaneously.

It is educational to roll your own select loop, but IO::Select is the way to get it done. 'man IO::Select' will tell you if you already have it, and how to use it.

After Compline,
Zaxo