Impossible to retreive the customer id of the session in an external script

[torresl]

I created an external script test.php of Magento But, i don' t succeed to retreive the customer id of the session
the script is as follows :
"

getCustomerId() ; echo "customer id :".$customer_id."\n"; ?>

"
To test, firstly, i authentificate a user via Magento.
Secondly, i launch the script test.php. But the customer id isn' t displayed.

Thanks to explain how to retreive session customer data in an erternal script ? .