my $ip = &get_IP;

sub get_IP {
    my $ip;
    do { $ip = <STDIN>; chop($ip); }
    while $ip !~ /^(\d+)\.(\d+)\.(\d+)\.(\d+)$/ ||
          $1 > 255 || $2 > 255 || $3 > 255 || $4 > 255;
    return $ip;
}