For example, I have instantiated 3 virtual machines in Amazon EC2-- I have also uploaded 3 different shell scripts to each of those machines... Now, I want to execute each of those 3 scripts... I know that each script will take some time to complete, so I want to start all 3 scripts together, and then wait for each of them to be complete...How do I do this? Is there a way to do this without using threads?