EXPLAINING UNIX
I wrote this book to explain how Unix works and to show you how to write system programs for Unix. Unix, still evolving after 30 years, has grown more complex, but it has not gotten more complicated. Its fundamental structure and design principles still apply. By understanding the structure, principles, and history, you will be able to read, enhance, and add to the vast accumulated literature of Unix programs. You also will have a lot of fun.
To make the ideas really clear, I present them in many forms: pictures, analogies, pseudocode, real code, experiments, exercises, and anecdotes. These explanations evolve from actual, useful problems and projects.
WHO IS PREPARED FOR THIS BOOK? You must know how to program in C. If you know C++, you should be able to follow the code and adapt quickly. You have to know about arrays, structs, pointers, and linked lists and be able to understand, and write, code that uses these.
You need not have used Unix, nor do you need to know about the internals of an operating system. In each chapter, we start with the user-level features of Unix. The question, 'What does that do?' at the user level leads inevitably to the system-level question, 'How does it work?'
You need to have access to a Unix system and a sense of adventure.
WHAT'S IN IT FOR ME? This book explains the components of a Unix system, what they do, the theory of how they work, and how to program using those components. You will also see how all these components fit together to form a coherent, intelligible operating system.
This book is based on a course, Unix Systems Programming, which I have taught at the Harvard Extension School since 1990. Students have described, on course evaluations and by e-mail years later, what the course gave them. One student said the course gave him 'the keys to the kingdom.' He understood Unix at the user, programming, and theory levels well enough to feel he could go anywhere and make sense of most problems. A physician in the course liked the case-study approach, comparing it to the way medical interns learn by working real problems.
Another student, one who went on to be a project leader at the Open Software Foundation, said the course taught him the ideas and skills he needed for that job.
FOR WHICH VERSION OF UNIX IS THIS WRITTEN? Almost all of them, including GNU/Linux. The focus of the book is the structure and skills that form the basis of all versions of Unix, not the specific variations, from one dialect to the next. Once you understand the main ideas, those details are easy to pick up.
