First of all: Do you really need the copy to be in parallel? If the files are stored on the same hard disk it won't be faster doing the writes in parallel.

Do you only copy the files or are you processing the data? Simple copying is best delegated to 'cp', i.e.  system("cp $from $to")
If you process the data, do it line by line or chunck by chunk and write parallel to all the files. No need to start threads at all.

If you still want to do it in parallel, you might just use fork(). See also http://www.perlmonks.org/?node_id=686182, a similar question just a few days ago.

You might provide some more detail next time and preferably some relevant parts of your code. Otherwise the monks have to guess a lot and write answers to questions you never asked.