use Encode::Punycode;
use Encode;
use Socket;

print getip( encode('Punycode', 'müller' ) . '.de' );

sub getip {
    my ($host) = @_;

    my $addr = gethostbyname( $host );

    die "Hostname $host doesn't exist.\n"
      unless $addr;

    return inet_ntoa( $addr );
}
^Z
Hostname xn--mller-ha.de doesn't exist.