Just use strictures (use strict; use warnings;) and you will see that there is an error on line xx - 3 that is causing the problem.

If that doesn't help (although it should, strictures always help) you may have to actually show us the code.

Update: Oh, I see you made a stealth update to your node. Still, you haven't told us which line the error occurs on

Update: on downloading your code and adding strictures I notice that $outdir is never initialised but is tested against.

Also flow is used as a file handle for multiple files inside a while loop and the files only ever have one line written to them. flow is only closed once (regardless of whether it was opened or not) outside the while loop.

$count is used in a print, but is never initialised.

File handle out is closed but it is never opened or otherwise used.