if( $ip=~ m{^\s*((\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3}))\s*$}s)
  { $ip= $1;
    my @fields=( $2, $3, $4, $5);
    foreach (@fields)
      { die "wrong field value: $_" if( $_ > 255); }
  }