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

open FILE1, '<', 'file1'  || die "Can't open file1: $!";
open FILE2, '<', 'file2'  || die "Can't open file2: $!";

my $line1 = <FILE1>;
my $line2 = <FILE2>;

while ($line1 && $line2) {
  if ($line1 == $line2) {
    $line1 = <FILE1>;
    $line2 = <FILE2>;
  } else {
    print $line1;
    $line1 = <FILE1>;
  }
}

print $line1 if defined $line1;
while ($line1 = <FILE1>) {
  print $line1;
}