Das Binding
$Entry8->bind( "<KeyRelease>", \&tiefevali($Entry8));




sub tiefevali
{

      if($Zufall eq '')  {$Zufall = 0; }

      my $tmp = $Zufall;
      $Zufall = $_[0]->get;

      if($Zufall =~ s/[^0-9]//gs)
      {
            $Entry8->delete(0,'end');
            $Entry8->insert(0,$tmp);    
            $Zufall = $tmp;
      }
}