my $ip_rgx = "\\d+\\.\\d+\\.\\d+\\.\\d+";
sub ipv4_chkip($) {
  my ($ip) = $_[0] =~ /($ip_rgx)/o;
  
  return undef unless $ip;
    
  # Check that bytes are in range
  for (split /\./, $ip ) {
    return undef if $_ < 0 or $_ > 255;
  }
  return $ip;
}