There've been some big changes in UNIX since we wrote the first edition in the early 1990s. We've made this second edition ready for the late 1990s-and, if we guessed right, for the start of the next century. Almost 550 of the more than 800 original articles were revised: many got small edits, but quite a few were completely rewritten. We included literally hundreds of reader suggestions and corrections. The CD-ROM has updated scripts and files, as well as binaries for today's UNIX platforms (including Linux). The biggest changes were:
The original split between the System V and BSD flavors of UNIX is still apparent, but it's less important. We've slanted the blend of options and commands more toward the POSIX utilities, including the GNU versions (which are close to POSIX now, but with other features too).
The shells tcsh and bash are much more common now than the footnotes we gave them before. Because bash seems to have combined the superior Bourne shell programmability with handy csh interactive features (and more!), we've given it more new coverage than tcsh. But there's plenty for tcsh users here: the first edition was very strong in csh, and almost everything you'll read about csh applies directly to tcsh. Overall, we've kept the first edition's emphasis on the core concepts of sh and csh that will help you use all UNIX shells.
The separate chapter on awk is gone; Perl is much more important than awk these days. Some of the original articles, including the handy nine-page, have been merged into other chapters. The short chapter on passwords and security is also history now. Just as the book we adapted it from (Practical UNIX and Internet Security) has almost doubled in size, the topic is too important these days for the short coverage we gave it before. As we did with Perl in both editions, we've left much of the security information for other books to cover in depth. (We've still got plenty of cool tips on filesystems and access permissions, though.)