But more importantly than that, you're forking at the wrong level of granularity. Forking involves overhead, so you want to have multiple long-lived copies of your program doing something. Furthermore it is not obvious to me whether your code will be bound by CPU or bound by I/O - but forking can work to your benefit either way.

If it takes a noticable amount time to process a file then my suggestion would be to use something like Parallel::ForkManager to fork off one job per file, and to keep a fixed number of jobs going at once. Have each output file written to another directory, and then reassemble the output into a single file later.

If individual files are virtually instantaneous to process but you have a lot of files, then you'll want to divide the list of files between copies of the program.

All of this advice, of course, is predicated on the assumption that you are using an OS where forking does something useful for you. Which means that I hope you're using something other than Windows.