# Finding Bugs

Finding Bugs: Debugging Scripts: bash -x, ShellCheck: A Second Pair of Eyes, Testing Scripts with bats.

Updated: November 10, 2026

1. [Debugging Scripts: bash -x](https://www.ask-codey.com/lessons/bash-debugging-scripts) (Journeyman): bash -x runs a script and prints every line before it runs, with its variables already filled in, so you can watch what the script really did; set -x and set +x trace one part only, and PS4 adds line numbers to the trace.
2. [ShellCheck: A Second Pair of Eyes](https://www.ask-codey.com/lessons/bash-shellcheck) (Journeyman): ShellCheck reads a script without running it and points out likely mistakes, each with its line, a code such as SC2086 and a plain message; the codes worth knowing are an unquoted variable, a cd that might fail and a loop over ls, and a disable comment silences one warning on purpose.
3. [Testing Scripts with bats](https://www.ask-codey.com/lessons/bash-testing-with-bats) (Freelancer): A test is a small script that runs yours and checks the result; bats runs a file of them, each written with @test, run and checks on $status and $output, in a fresh folder from setup, and reports each one as passed or failed, with the line that failed.

Source: https://www.ask-codey.com/courses/bash-in-depth/topics/bash-finding-bugs