If I understand your question correctly, the easiest way to do it is to make the $url a separate variable, instead as part of the GET. Also, I don't know what you are try to accomplish if you don't want the content. Are you just tring to detect whether the server is up? There are easier ways to do that.

for my $i (0..10000) {
    
  my $url = sprintf("http://dms-schule.bildung.hessen.de/suchen/suche_
+schul_db.html?show_school=5503,%d", $i);
    
  my $request = HTTP::Request->new(GET => $url );
      
  $request->header('Accept' => 'text/html');
    my $response = $ua->request($request);
      if ($response->is_success) {
         $pagecontent = $response -> content;
       }
   
     my $request = POST $url, 

    # check the outcome 
     if ($res->is_success) { 
       print "Success  $url  \n"; #  print out all the URLS that were 
+fetched!  
     } else { 
       print "Error: $url " . $res->status_line . "\n"; 
     }

}  # end of for $i loop
[download]