I may be misunderstanding what you're trying to achieve, but you can simulate the bash '&' operator for a running process by pressing ctrl-Z to suspend the process and send it to the background, then running 'bg' to continue the process in the background.

Yeah I was unclear there - I meant the other use of the & operator, 'foo & bar' where bar starts after foo completes. AFAIK, if you ran foo by itself, there's no way to make bar automatically run after foo completes.

I had that need and made something a lot simpler: https://github.com/tv42/wait-for-pid

think you mean && there :)

This type of scene is called a Cornell box, often used to test rendering capabilities.

https://en.wikipedia.org/wiki/Cornell_box