To run a shell script on Llamalab Automate you can install Termux, Termux:Api and Termux:Tasker (from F-Droid). Then configure Automate app permission to use Termux Run Command.
Now you can add a Tasker Plug-in block, choose Termux:Tasker and the path of the script (absolute path or relative to folder ~/.termux/tasker/).