Here's the extra-quick but naughty version. It should work just peachy with concatenating text files.

use strict;
use warnings;

my $destination = pop @ARGV;
open OUT, ">$destination"
    or die "Couldn't create the concatenated file $destination: $!\n";
print OUT while (<>);
close OUT;
[download]

The '<>' is a spicy bit of Perl that uses your command-line args as file names.