Wait for process with name to spawn in Bash

I want to write a Bash script that runs in a background, waiting for a command to spawn.

Suppose I ran script.sh which waits for ls. After I run ls, it should trigger actions?

You can use pgrep to create a while loop like this:

#!/bin/bash

# Wait for particular process to run
while ! pgrep "process-name " > /dev/null; do

    # Set optional delay
    sleep .1

done

# Do something when the process has started
your-commands-here

You need to adjust the delay, so that it "catches" the process you run. This of course works best if it should detect a service that doesn't stop again, but this will work for any command that takes longer time to finish than the delay you have set (ls is a bad example, since it only takes milliseconds to finish the process).

Also see this post on Unix and Linux.