A list of resources on shell scripting.

A basic introduction to shell scripting using the Bourne shell.
Another basic introduction to shell scripting by Apple.
The classic Linux guide on advanced bash shell scripting.
Chapter of an old book published by VA Linux with some useful information on advanced shell scripting topics.
Short list of best practices for bash scripting. Basic, but still useful as a reminder.
A four-minute guide to reliable, performant, and reusable Bash scripts.
A page explaining how to make bash scripts work in the dash shell and, along the way, how to make them POSIX compliant.
The goal of this book is to document commonly-known and lesser-known methods of doing various tasks using only built-in POSIX sh features.
A very useful list of pitfalls when using the bash shell.
A simple command line tool to find bugs in your shell scripts.
The man page for the checkbashisms command, which checks for bashisms in scripts.