Updated on September 14th, 2021 in #linux

Using Bash set -x to Help Debug Why a Script Isn't Working

Bash has an x flag or you can use set -x in a script to print a trace of commands and variables. It's really handy!

Quick Jump: Demo Video

If you’re wondering why a variable isn’t outputting what you expect or why a command you’re trying to run isn’t working as expected then running bash -x [YOUR_SCRIPT] or defining set -x in your script might be exactly what you need.

In this video we’ll see how both work and how they help to debug shell scripts.

Demo Video

Timestamps

• 0:08 – Going over the demo script really quick
• 1:07 – Running the script to demonstrate the error
• 2:23 – It worked manually but not in the script, hmm
• 3:11 – How bash -x helps us find the problem within seconds
• 5:16 – A few ways to solve this specific error around passing in arguments
• 6:17 – Making ShellCheck happy
• 6:58 – Parsing arguments and one difference between $* and $@ with Bash
• 9:09 – Why I like naming variables instead of using $1, $2 and $@
• 10:28 – Using set -x in your Bash script to apply bash -x by default
• 11:28 – Does it with work POSIX complaint shell scripts?

Reference Links

• https://nickjanetakis.com/blog/replacing-make-with-a-shell-script-for-running-your-projects-tasks
• https://nickjanetakis.com/blog/linting-and-improving-your-bash-scripts-with-shellcheck

When was the last time -x helped you debug something? Let me know below.