How to debug shell / bash scripts

While executing the bash scripts, if you want to debug them i.e you want to trace the exact sequence of steps that get executed, continue reading this post below.

Just below the shebang line on top of every script, type this :

set -x

That's it.

Let's take the example of killing a process / application using shell script that we saw in our previous post. Assuming you have opened the application - TextWrangler and want to close it using a bash script.

#!/bin/bash

set -x

kill -9 `ps -ef | grep TextWrangler | awk '{print $2}'`;

Now here's the output for the same :

++ ps -ef

++ grep TextWrangler

++ awk '{print $2}'

+ kill -9 24677 24678 24682

Note that 24677 24678 and 24682 are all PID's of all processes associated with TextWrangler. In this way you can track the flow of the script in which the tasks get executed. Debugging can be of great help if you have a complex flow of program and need to identify the sequence of steps in which they are executed.