open my $url_fh, '<', 'urls.txt'
    or die "Can't read 'urls.txt': $!";
chomp( my @urls = <$url_fh> );
close $url_fh   or die "close() failed: $!";

open my $code_fh, '<', 'data.txt'
    or die "Can't read 'data.txt': $!";
chomp( my @codes = <$code_fh> );
close $code_fh   or die "close() failed: $!";

my @joined = map {
                   my $url = $_; 
                   map { $url . $_ } @codes
                 } @urls;