...
#holt vorhandene id aus cookie, falls vorhanden...
$cookie = $request->cookie(-name=>"session");
$session = new CGI::Session("driver:File", $cookie,{'Directory'=>"$session_dir"}) or die $!;

$session->param('name', 'peter');
$session->flush();
$id = $session->id();
print "Set-Cookie: session=$id; domain=$ENV{'HTTP_HOST'}; path=/\n";
...