#!/usr/bin/perl 
use warnings;
use strict;

my @final; # Joined lines will be in here

open(URLS, '<', 'urls.txt') or die $!; # I can never remember if < is read
chomp(my @urls = <URLS>); # Every line of URLS is a different element in @urls
close URLS;

open(CODES, '<', 'data.txt') or die $!;
chomp(my @codes = <CODES>);
close CODES;

foreach my $url (@urls) { # For every element (line) in @urls,
    foreach my $code (@codes) { # and for every element in @codes,
        push @final, $url$code; # append the two and push it into @final
    }
}