use constant REGEXP_HOSTNAME      => qr/^([\w\-.]+)$/;
use constant REGEXP_IPADDR        => qr/^((?:(?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})))$/;

sub valid_hostname
{
   my $value = shift;

   return 0 unless $value =~ REGEXP_HOSTNAME;
   return 0 unless index($value, ".") > 0;

   my @parts = split/\./, $value;
   my $valid = @parts;

   foreach my $label (@parts)
   {
      $valid = 0 if (length $label > 63) or ($label =~ m!^\-!) or ($label =~ m!\-$!);
      last unless $valid;
   }

   $valid = 0 if $parts[-1] =~ m!^\d.*!;

   return $valid;
}

sub valid_ipaddr
{
   my $value = shift;
   return $value =~ REGEXP_IPADDR;
}

sub valid_host
{
   my $value = shift;
   return valid_hostname($value) || valid_ipaddr($value);
}

use Net::IDN::Encode;

use constant REGEXP_HOSTNAME => qr!^[\w\-.]+$!;
use constant REGEXP_IPADDR   => qr!^((?:(?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})))$!;

sub host_toidn
{
   return domain_to_ascii(shift);
}

sub host_fromidn
{
   return domain_to_unicode(shift);
}

sub valid_hostname
{
   my $value = host_toidn(shift);

   return 0 unless $value =~ REGEXP_HOSTNAME;
   return 0 unless index($value, ".") > 0;

   my @parts = split /\./, $value;
   my $valid = scalar @parts;

   foreach my $label (@parts)
   {
      $valid = 0 if (length $label > 63) or ($label =~ qr!^\-!) or ($label =~ qr!\-$!);
      last unless $valid;
   }

   $valid = 0 if $parts[-1] =~ qr!^\d.*!;

   return $valid;
}

sub valid_ipaddr
{
   my $value = shift;
   return $value =~ REGEXP_IPADDR;
}

sub valid_host
{
   my $value = shift;
   return valid_hostname($value) || valid_ipaddr($value);
}

use constant REGEXP_IPADDR   => qr!^((?:(?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})[.](?:25[0-5]|2[0-4]\d|[0-1]??\d{1,2})))$!;
sub valid_ipaddr
{
   my $value = shift;
   return $value =~ REGEXP_IPADDR;
}

sub valid_ipaddr
{
  my $value = shift;
  my @teile = split /\./, $value;
  # zuerst mal prüfen, ob es sich um eine korrekte Adresse handelt
  return(0) if @teile != 4;       # es müssen 4 Teile sein
  foreach (@teile) {              # in jedem Teil
    return if /\D/;               #    dürfen nur Ziffern vorkommen
    return if $_ > 255 or $_ < 0; #    zwischen 0 und 255
  }
  # hier können evtl. noch weitere Prüfungen folgen (127.0.0.1)
  return(1); # o.k.
}
# untested

$valid = 0 if $parts[-1] =~ qr!^\d.*!;