sub CheckIfUserIsLoggedIn
{

use CGI::Session;
my ($sid,$session,$userid);

$cgi=new CGI;
$sid=$cgi->cookie("CGISESSID")||undef;
$session = new CGI::Session("driver:DB_File",undef,{Directory=>'/tmp'});
$userid = $session->param("userid");

if ($userid eq "")
{
print "Content-type: text/html\n\n";
print "You are not logged in!!\n\n";
exit;
}
else
{
## display whatever I want to this user
}
}