print "Enter the IP-range e.g. 192.168.2.0!\n";
print "IP-range: ";
my $range = <STDIN>;
while ($range !~ /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/)
{
      print "Wrong IP-range. Enter right IP-range e.g. 192.168.2.0!\nIP-range: ";
      $range = <STDIN>;
}