Specify -thread if you want a thread created to run the procedure. This will allow the scheduler to continue with other scheduled procedures. Specifying -thread is appropriate in situations where the script will not return immediately, such as when the script performs network activity.
Specify -once if you want the script to run only one time. The default is that the script will be re-scheduled after each time it is run.
ns_schedule_weekly returns an id number for the scheduled procedure that is needed to stop the scheduled procedure with ns_unschedule_proc.