open HOSTS, "</etc/hosts"; # Or "<C:\\WINDOWS\\hosts";
my %hosts = map{
  my $ip, $hn, @hn;
  if (not /^\s*#/) {
    chomp; s/\s*#.*$//;
    ($ip, @hn) = split /\s+/, $_;
  }
  map { $_ => $ip }, @hn;
}<HOSTS>;