...
$session = new CGI::Session("driver:File",undef,{'Directory'=>"$session_dir"}) or die "$!";

### write the Session-variables
$session->param('name', 'ulf');
$session->expire('+2h');

### Send the linked cookie to the client
$id = $session->id();
print "Set-Cookie: session=$id; domain=$ENV{'HTTP_HOST'}; path=/\n";

### Session-data saving...
$session->flush();
...