file systems

Back when dinosaurs roamed the earth and NCR made Unix computers I first started to program for a living. Back then when someone said 'script' they meant a shell script, generally for a Bourne shell.

Now that we have languages such as Perl and Python, much of shell scripting has been forgotten. The need still arises for the times and places where running Perl would be just that little bit too much overhead; cron jobs, process start and stop scripts, even machine start and stop scripts. For these we could best go back to the old ways. Combining the power of the common Unix tools, pipes and scripts in a fairly obscure and slightly arcane syntax is not easy to pick up, though the language's simplicity does, in some ways, make it easier than more complex ones such as Perl. Unix Shell Programming, Third Edition does a good job at introducing shell programming and I found it an excellent book when I needed a refresher.

I don't want to sell this volume short: you won't just learn about shell programming. The first ninety or so pages provide an excellent guide to getting the best out of the shell, and the last chapter is devoted to the features specific to an interactive shell such as command-line editing and using the history.

The authors have chosen to use the POSIX standard Bourne shell ('bash', available on many *nix systems, is a superset of the POSIX standard). That seems the right decision, given that it is so universally available and usually the default shell.

The book is well structured, starting out with a brief look at *nix operating systems before introducing the shell followed by some basic tools; cut, paste, sed, tr, grep, sort and uniq. One minor quibble, the book explains how to redirect STDOUT to a file and STDERR to a file, but not how to redirect both to the same file. That aside, these few chapters provide a good introduction to the shell.

The text goes on to systematically explore shell programming starting with variables and arithmetic. The chapters are kept short, in a good order and have a number of exercises at the end of each. The structure of the book and the order each new concept is introduced is well thought out; at each stage small examples are given that only use material already introduced and are complete in performing a task. In early chapters they are fairly trivial but by the end there is a fairly complete rolodex program written in shell script that would be a good model for anything you wished to do.

There is also a good summary of the shell syntax and common commands in Appendix A and good 'Further Information' in Appendix B. Kudos must go to the authors for a list of books for further reading that is not ashamed of mentioning other publishers, indeed they say "One of the best sources of books on Unix-related topics is O'Reilly and Associates" and list volumes from them before mentioning their own publishers.

There are some small typographic errors in the text but I did not find any in the script examples I tried. I found it to be well written and readable throughout, perhaps an advantage of a third edition in a slow moving technology.

I would recommend everyone read this book once or twice, it provides a comprehensive, well written tutorial on one of the most basic (and often overlooked) tools at your disposal. Even Windows users could install Cygwin and gain the benefit of a good POSIX compliant shell and this book. It also has the advantage that once purchased it will be useful for many, many years to come - the language has not changed noticeably in twenty five years and should not change in another twenty five.

"UNIX Shell Programming, 3rd Ed" (USP3E) is probably the book to buy if you're a beginning UNIX user with dreams of writing shell scripts. The book does a good job of explaining many of the key concepts needed to get real work done on UNIX systems. While readers with advanced backgrounds will prefer a book like "Mastering UNIX Shell Scripting" by Randal Michael, USP3E will please most UNIX scripting newbies.

USP3E begins with a review of the basics -- working with files and directories, redirecting input/output, pipes, and the shell itself. Chapter four's discussion of regular expressions is generally useful, although "saving matched characters" on p. 64 was confusing. This made the "command substitution" material on p. 129 unclear. Chapter six was devoted to the use of different sorts of quotes, which seems excessive until one realizes the significant differences between using single and double quotation marks in scripts. Attention to detail like this, along with generous inclusion of sample scripts, helped this book earn a strong rating.

While the book includes examples of using sed, awk is not mentioned. Sed could have received more coverage as well. While the authors direct interested readers to other books, perhaps a future edition might include chapters devoted to sed and awk? While the publisher's site doesn't mention a source for errata, it is available by contacting the authors.

Overall, I liked this book. It is up-to-date and compares favorably to the other books I consider reading to learn more about UNIX shell scripting. Armed with the knowledge gained from USP3E, readers should be equipped to automate some routine tasks. They will also be able to progress to more advanced shell scripting resources.