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Before we begin

We will set up a few conventions to help with this tutorial.

Every lesson is its own project

Each lesson has its own source code, README, and Makefile. You can build each one by entering its directory and typing gmake test. That will build and execute the lesson to prove to you that it works. Your task is to read the code and understand why it works. To make this easy, each lesson builds on the prior one by adding the least possible amount of code.

Error handling is everywhere

You will see lines like this sprinkled throughout the source code:

if (result == -1) err(1, "A terrible thing has happened");

This makes the code somewhat messier to read, but it is a great aide to experimentation: as soon as you modify the lesson and something breaks, these error messages will help you understand what system calls are failing, and the associated man pages can help you figure out why.

Some words of encouragement

Doors are unusual, but you'll get the hang of them. If you get confused or frustrated, take a break and come back to it. They'll be here when you get back.

Check for Understanding

1. What system header defines err?
2. Why bother exiting early for an error instead of just returning normally?