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How to run Bash commands in parallel and wait before all commands finished

In this article i will explain how you can run commands in parallel and make sure you wait until all commands and have finished and then move forward.


Say you have a script which downloads few files or yu have to compile different maven project(independent of each other) or something else which can run in parallel and you have got a good machine which can run these tasks in parallel so that overall you can run the full task in lowest time.

For this you can use back ground task and wait from unix.

When you add & to any command that command runs in background

What is wait command?
wait is a built-in command of Linux that waits for completing any running process. wait command is used with a particular process id or job id. When multiple processes are running in the shell then only the process id of the last command will be known by the current shell. If wait command is executed this time, then it will be applied for the last command.

If no process id or job id is given with wait command then it will wait for all current child processes to complete and returns exit status.

Here goes an example


echo First Group:
command A &
command B &
command C &
wait

#Command D will not run untill Command A,B, C all finished
echo Second Group:

command D &
command E &
wait

#Command F will not run untill Command A,B, C,D and E all finished
command F 


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