Can I auto-shutdown my server if my bandwidth limit is reached?

Hi,

It is not recommended to shutdown server system in anyway, we can have other options to maintain the bandwidth at Server System.

Regards 

Yes, If you can combine shell programming to some scheduling process "or cron for linux"

but, its complex and you need to have the skills to write .bat or .sh. Finally, you must know the function in use output since you need to evaluate bandwidth in regular basis and the output me be read from the process or function that is going to fire action for the cron or the cron job it self or immediately shutdown which not applicable for working system 

Note: you must notify end users that server is going to be turned off and you must has plan B in such situation

I think I describe it in complex way since it's complex and I would like always to solve system related problem by shell coding for security reasons.

Yes definitely you can auto-shutdown your server if your bandwidth limit is reached.