From time to time my Mac is doing stuff which takes quite awhile. Converting images, converting videofiles between formats or other stuff, which may take a long time (but reasonable predictable).
In those cases I run a little command in the terminal, to automatically shut down the Mac upon completion:
sudo shutdown -h +120
This command sets a timer which shutdown the machine after two hours (the 120 parameters being after 120 minutes).
The command has no UI but sets a time. If you need to cancel the shutdown, simply write:
sudo killall shutdown
… and this will cancel the shutdown (if any is set). It does not tell if the shutdown timer was killed or not, but you can verify it by these commands:
if ps -C shutdown > /dev/null; then echo "Shutdown is pending"; else echo "Shutdown is not scheduled"; fi
This command will tell you if a shutdown is pending or not. As these are unix commands they should also work on any linux server if needed.