There is no direct access to a shell prompt on NetBackup Appliances. They have been hardened to remove that.
In addition, running an unauthorized script on an Appliance can, under certain conditions, result in the removal of Support.
If you're trying to run a script to run NetBackup commands to change things like Policies and Schedules (like my company does to acomindate their Fiscal Year) then I'd recomend setting up a small Linux or Windows VM and configuring it as a Media Server. Then all those commands would be available.
If you're trying to monitor or otherwise interrogate the Appliance then you may need to look at something like the Alerts in OpsCenter. Or use the small VM Media Server approach so you can run Media Server type commands to interrogate the Appliance...