Linux shell script asynchronous commands and notification when completed

Question

I have a script which updates a web application. The web application is spread across 2 servers. Here is a rundown of the script

1. The shell script updates the git repository.
2. The shell script stops the application server.
3. The shell script stops the web server.
4. The shell script instructs the application server to checkout the latest git update.
5. The shell script instructs the web server to checkout the latest git update.
6. The shell script starts the application server.
7. The shell script starts the web server.

Each of the 7 steps are done one after the other synchronously. The total run time is approximately 9 seconds. To reduce downtime however, many of these steps could be done asynchronously.

For example, step 4 and 5 could be done at the same time. I want to start step 4 and 5 asynchronously (e.g. running in the background), but I cannot find how to wait until they are both completed before going further.

Answer 1

You might want to use command grouping to maintain which steps need to be synchronous:

step1
( step2 && step4 && step6 ) &
( step3 && step5 && step7 ) &
wait && echo "all done"