Well, your $/ = ""; causes your while (<F>) to slurp the entire file into $_ and the while statement executes once. Setting $\ = ""; is somewhat unncecessary as that's its default (unless you run with -l). The structure of your foreach is...umm...interesting. Splicing the array is unnecessary since it falls out of scope at the end of the outer while. I don't know what $cat contains...I suspect it's a program but? Does the program return different data each time it's called? Beyond that, what is this script doing that you aren't expecting?

antirice    
The first rule of Perl club is - use Perl
The ith rule of Perl club is - follow rule i - 1 for i > 1