[Q] Detect when superuser permission denied in app topic

Hi,

I am developing an app that requires root permissions to run some shell commands to capture ouput. I am executing the "su" command to get root permission and it works fine when the su permission is granted. However I would like to know how to detect if the permission was denied? as there does not seem to be any exception or other indication when this is denied.

Any help would be much appreciated.