#!/usr/bin/perl -w
use strict;

my ($string1, $string2);

$/ = undef;

open (FILE1, "< x") || die "Cannot open file : $!";
open (FILE2, "< y") || die "Cannot open file : $!";
open (FILE3, "> z") || die "Cannot open file : $!";

$string1 = <FILE1>;
$string2 = <FILE2>;

print FILE3 join('', $string1, $string2);

close (FILE1);
close (FILE2);
close (FILE3);