Linux Basic — Debugging Techniques

Debugging Techniques

A robust script (last chapter) fails loudly. But when it does fail, you still have to find the bug. Bash gives you tracing, a powerful static analyser (ShellCheck), and a small set of conventions for adding diagnostics on demand.

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What You Will Learn

By the end of this chapter you will be able to:

• Enable command tracing with set -x and customise the PS4 prompt
• Run a one-off trace with bash -x script.sh
• Use shellcheck to catch dozens of common bugs before they happen
• Add a toggleable debug mode to your scripts
• Recognise (and avoid) the 10 most common shell-scripting bugs

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Topics in This Chapter

#	Topic	Description
1	set -x (xtrace)	enable tracing, custom PS4
2	bash -x Flag	trace a single run from outside
3	ShellCheck	the static analyser everyone should run
4	Debug Mode	DEBUG=1 toggles + per-section trace
5	Common Scripting Bugs	the top 10 things that bite
6	Practice Exercises	Hands-on tasks

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The Debugging Mindset

Two rules to internalise:

1. Make the script tell you what it’s doing. Tracing turns “this doesn’t work” into “I can see exactly where it broke.”
2. Use static analysis first. ShellCheck finds 90% of bugs before you ever run the script — including bugs that only manifest in edge cases.

The single best workflow is:

shellcheck script.sh && bash -n script.sh && bash -x script.sh

• shellcheck — static analysis (catches quoting bugs, unused vars, bad globs)
• bash -n — parse-only, no execution (catches syntax errors)
• bash -x — trace the actual run

Combine those three before running anything destructive.

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Next → set -x (xtrace)