I dont mind at all to help someone when i can, but it always helps if you atleast post some example files, and some code that you have tried.

But just to start it off, this is how I slurp a directories contents usually:

use strict;
use warnings;
use diagnostics;

use File::Slurp;

my @files = read_dir($ARGV[0]);

foreach my $file(@files){
    next if (-d $file); #skip directories
    print "processing $file\n";
    ...do stuff...
}
[download]

I know your wanting to add everything from file 2 and 3 and 4 to file 1 if it does not exist in file 1, which could be pretty straight forward, but without any example files or code, then I dont know what you really are hoping to end up with in the end.