Mike G's "Bash-Programming-Intro HOWTO".
Chet Ramey's "Bash FAQ".
Greg's Wiki, many Bash related pages
Shell scripts at SHELLdorado
Example shell scripts at Noah Friedman's script site.
Examples from the The Bash Scripting Cookbook, by Albing, Vossen, and Newham.
Steve Parker's Shell Programming Stuff. In fact, all of his shell scripting books are highly recommended.
An excellent collection of Bash scripting tips, tricks, and resources at the Bash Hackers Wiki.
Giles Orr's "Bash-Prompt HOWTO".
The Pixelbeat command-line reference.
Very nice sed, awk, and regular expression tutorials at The UNIX Grymoire.
The GNU sed and gawk manuals. As you recall, gawk is the enhanced GNU version of awk.
Tips and tricks at Linux Reviews.
Trent Fisher's groff tutorial.
David Wheeler's Filenames in Shell essay.
"Shelltris" and "shellitaire" at Shell Script Games.
YongYe's wonderfully complex Tetris game script. (In Bash script and other languages)
The Linux USB subsystem (helpful in writing scripts affecting USB peripherals).
Aurelio Marinho Jargas has written a Regular expression wizard. He has also written an informative book on Regular Expressions, in Portuguese.
Ben Tomkins has created the Bash Navigator directory management tool.
Edited by Peter Denning, "Computers Under Attack: Intruders, Worms, and Viruses", ACM Press, 1990, 0-201-53067-8.
This compendium contains a couple of articles on shell script viruses.
Ken Burtch, "Linux Shell Scripting with Bash", 1st edition, Sams Publishing (Pearson), 2004, 0672326426.
Covers much of the same material as the ABS Guide, though in a different style.
Daniel Goldman, "Definitive Guide to Sed", 1st edition, 2013.
This ebook is an excellent introduction to sed. Rather than being a conversion from a printed volume, it was specifically designed and formatted for viewing on an ebook reader. Well-written, informative, and useful as a reference as well as a tutorial. Highly recommended.
Dale Dougherty and Arnold Robbins, "Sed and Awk, 2nd edition", O'Reilly and Associates, 1997, 1-156592-225-5.
Unfolding the full power of shell scripting requires at least a passing familiarity with sed and awk. This is the classic tutorial. It includes an excellent introduction to Regular Expressions. Recommended.
Jeffrey Friedl, "Mastering Regular Expressions", O'Reilly and Associates, 2002, 0-596-00289-0.
Still the best all-around reference on Regular Expressions.
Aeleen Frisch, "Essential System Administration", 3rd edition, O'Reilly and Associates, 2002, 0-596-00343-9.
This excellent manual provides a decent introduction to shell scripting from a sys admin point of view. It includes comprehensive explanations of the startup and initialization scripts in a UNIX system.
Stephen Kochan and Patrick Wood, "Unix Shell Programming", Hayden, 1990, 067248448X.
Still considered a standard reference, though somewhat dated, and a bit "wooden" stylistically speaking. [1] In fact, this book was the ABS Guide author's first exposure to UNIX shell scripting, lo these many years ago.
Neil Matthew and Richard Stones, "Beginning Linux Programming", Wrox Press, 1996, 1874416680.
Surprisingly good in-depth coverage of various programming languages available for Linux, including a fairly strong chapter on shell scripting.
Herbert Mayer, "Advanced C Programming on the IBM PC", Windcrest Books, 1989, 0830693637.
Excellent coverage of algorithms and general programming practices. Highly recommended, but unfortunately out of print.
David Medinets, "Unix Shell Programming Tools", McGraw-Hill, 1999, 0070397333.
Pretty good treatment of shell scripting, with examples, and a short intro to Tcl and Perl.
Cameron Newham and Bill Rosenblatt, "Learning the Bash Shell", 2nd edition, O'Reilly and Associates, 1998, 1-56592-347-2.
This is a valiant effort at a decent shell primer, but sadly deficient in its coverage of writing scripts and lacking sufficient examples.
Anatole Olczak, "Bourne Shell Quick Reference Guide", ASP, Inc., 1991, 093573922X.
A very handy pocket reference, despite lacking coverage of Bash-specific features.
Jerry Peek, Tim O'Reilly, and Mike Loukides, "Unix Power Tools", 3rd edition, O'Reilly and Associates, Random House, 2002, 0-596-00330-7.
Contains a couple of sections of very informative in-depth articles on shell programming, but falls short of being a self-teaching manual. It reproduces much of the Regular Expressions tutorial from the Dougherty and Robbins book, above. The comprehensive coverage of UNIX commands makes this book worthy of a place on your bookshelf.
Clifford Pickover, Computers, Pattern, Chaos, and Beauty, St. Martin's Press, 1990, 0-312-04123-3.
A treasure trove of ideas and recipes for computer-based exploration of mathematical oddities.
George Polya, "How To Solve It", Princeton University Press, 1973, 0-691-02356-5.
The classic tutorial on problem-solving methods (algorithms), with special emphasis on how to teach them.
Chet Ramey and Brian Fox, "The GNU Bash Reference Manual", Network Theory Ltd, 2003, 0-9541617-7-7.
This manual is the definitive reference for GNU Bash. The authors of this manual, Chet Ramey and Brian Fox, are the original developers of GNU Bash. For each copy sold, the publisher donates $1 to the Free Software Foundation.
Arnold Robbins, "Bash Reference Card", SSC, 1998, 1-58731-010-5.
Excellent Bash pocket reference (don't leave home without it, especially if you're a sysadmin). A bargain at $4.95, but unfortunately no longer available for free download.
Arnold Robbins, "Effective Awk Programming", Free Software Foundation / O'Reilly and Associates, 2000, 1-882114-26-4.
The absolute best awk tutorial and reference. The free electronic version of this book is part of the awk documentation, and printed copies of the latest version are available from O'Reilly and Associates.
This book served as an inspiration for the author of the ABS Guide.
Bill Rosenblatt, "Learning the Korn Shell", O'Reilly and Associates, 1993, 1-56592-054-6.
This well-written book contains some excellent pointers on shell scripting in general.
Paul Sheer, LINUX: Rute User's Tutorial and Exposition, 1st edition, , 2002, 0-13-033351-4.
Very detailed and readable introduction to Linux system administration.
The book is available in print, or on-line.
Ellen Siever and the staff of O'Reilly and Associates, Linux in a Nutshell, 2nd edition, O'Reilly and Associates, 1999, 1-56592-585-8.
The all-around best Linux command reference. It even has a Bash section.
Dave Taylor, "Wicked Cool Shell Scripts: 101 Scripts for Linux, Mac OS X, and Unix Systems", 1st edition, No Starch Press, 2004, 1-59327-012-7.
Pretty much what the title promises . . .
"The UNIX CD Bookshelf", 3rd edition, O'Reilly and Associates, 2003, 0-596-00392-7.
An array of seven UNIX books on CD ROM, including UNIX Power Tools, Sed and Awk, and Learning the Korn Shell. A complete set of all the UNIX references and tutorials you would ever need at about $130. Buy this one, even if it means going into debt and not paying the rent.
Update: Seems to have somehow fallen out of print. Ah, well. You can still buy the dead-tree editions of these books.