Creating a "Demo Mode" for CNC-based machines

I have two current projects - a CNC etch-a-sketch and a sand plotter, both GRBL controlled - and I would like to create a "Demo Mode" for each of them. The idea would be that there would be 5-10 designs that the machine would print, one after the other. I use raspberry pis running octoprint to control my 3d printers, and I'm guessing I would need to use a similar setup - a raspberry pi to store and send the gcode to the controller, but I'm not sure how to get the pi to do that. Would it be as simple as a short program that loads the file, sends it out the serial port, waits a bit, then does the next one? I've done a little coding (or at least modifying others' code) but I'm not a programmer. Any suggestions or examples of how to accomplish this would be greatly appreciated.

If all I'm doing is reading and sending the gcode, do I need a raspberry pi? Could another arduino handle the task?

Thanks!