Get Stop in accounting do some action

Hello everyone I need to update some check and replay attribute in database when get stop in accounting and the session is finish i need to know in which section of virtual server file ( sites-enabled/default) i need to put unlang script (and/or perl script) ? and how i can check in script if accounting get stop packet , read some radacct fild of that session to do some calculate and do some query in database in radcheck and radreplay . Best regards.