How to run a background shell script which itself lauches two background processes?

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http://stackoverflow.com – To start with, I am a beginner to programming etc so apologies for lack of professionally accurate terminology in my question but hopefully I will manage to get my points across! Would you have any suggestions how in bash or tcsh I can run a long background process which itself launches a few programs and has to run three long processes in parallel on different cores and wait for all three to be completed before proceeding...? I have written a shell script (for bash) to apply an image filter to each frame of a short but heavy video clip (it's a scientific tomogram actually but this does not (HowTos)