Bash script code quality

This repository demonstrates via its commit history the process of improving the code quality of a Bash script. The commit messages explain the introduced changes and their motivation while this document lists the used tools and references.

Tools

The ShellSpec framework is used for testing as it employs a behaviour-driven development approach with a domain-specific language that helps create easily readable tests. In addition, it provides many options for mocking and other useful testing features.

The other essential tool to detect error-prone code or even bugs is the static code analyser ShellCheck. It can be run in the command line or integrated into editors.

For example, for the presentation of the process, the ALE plugin and Airline status line for Vim have been used to show the annotations in the editor.

The Flog plugin for Vim has been used to check out the commits one after another, so tests could be run at the various stages.

References

Calling Docker for separate commands

• Stack Overflow – What is the runtime performance cost of a Docker container?

Variables

• Unix & Linux Stack Exchange – Are there naming conventions for variables in shell scripts?

• Bash reference manual – Bash builtin commands, local

Initialise and run ShellSpec

• ShellSpec – Project directory
• ShellSpec – runs specfile using /bin/sh by default
• ShellSpec – How to use ShellSpec with Docker, Run simple with helper script and extra hooks

Unit testing single-file scripts

• ShellSpec – Using run source
• References

Error handling

• Stack Overflow – How to exit if a command failed?

• Bash FAQ – Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?

• Bash reference manual – Special parameters, ?

• Bash reference manual – Bourne Shell builtins, exit

Writing output

• Stack Overflow – Why use printf '%s\n' “message”?

• Unix & Linux Stack Exchange – Why is printf better than echo?

• Bash reference manual – Bash builtin commands, printf

ShellCheck shell declaration

• ShellCheck wiki – Directive, shell

Custom assertion counting occurrences of a string

• Bash reference manual – Here strings
• Bash reference manual – Shell parameter expansion, ${parameter:?word}
• Bash reference manual – Conditional constructs, ((…))

Match function arguments

• Bash reference manual – Special parameters, *
• Bash reference manual – Pattern matching, *

Command substitution

• Bash FAQ – Why is $(...) preferred over ... (backticks)?

• Bash reference manual – Command substitution

Working with calculation results

• Bash reference manual – Arithmetic expansion

Define multiline string variables

• Stack Overflow – How to assign a heredoc value to a variable in Bash?

• Bash reference manual – Here documents

• Bash reference manual – Shell parameter expansion, ${parameter/pattern/string}

• Bash reference manual – ANSI-C quoting

Call original command instead of mock

• ShellSpec – Support commands, Execute the actual command within a mock function

Prefer [[ ]] test over [ ] in Bash

• Bash FAQ – What is the difference between test, [ and [[ ?
• Bash Guide – Practices, Choose your shell

Define default value for variable

• Bash reference manual – Shell parameter expansion, ${parameter:-word}

Problems with looping over find output

Bash Pitfalls – for f in $(ls *.mp3)

Read find output into array

• Bash FAQ – How can I find and safely handle file names containing newlines, spaces or both?

• Stack Overflow – How can I store the “find” command results as an array in Bash

• Unix & Linux Stack Exchange – Bash: pipe 'find' output into 'readarray'

• Bash reference manual – Arrays

• Bash reference manual – Grouping commands, {}

• Bash reference manual – Bash builtin commands, readarray

• Bash reference manual – Process substitution

• Bash reference manual – Job control builtins, wait

• Bash reference manual – Special parameters, !

Useless use of cat

• Wikipedia – Cat, Useless use of cat

Execute command upon script termination

• Bash reference manual – Bourne Shell builtins, trap