The bash shell is powerful software for Linux, Unix, and other systems. It comes as a standard part of most Linux distributions ("distros") and most Unix systems. You can even get versions that will run on MS-Windows systems (see cygwin). It is the "command line interpreter" that you get when you bring up a terminal window like Terminal or Konsole.
Here is a pile of helpful reference documents (not for beginners) dealing with bash.
Great Bash video, from O'Reilly, will teach you the fundamentals of bash shell programming. Beginning with simple shell scripts and progressing to complex, automated system administration and file management tasks, you'll get a firm handle on control structures and the decision-making abilities of the bash environment. By the time you're done, you'll have written more than twenty complex shell scripts. Join Carl Albing, co-author of the bash cookbook, for screencast lessons of some great bash! Buy it today; use it every day.
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Carl and JP are happy to share what they know about bash.
Carl Albing is currently a Distinguished Visiting Professor in the Department of Computer Science at the U.S. Naval Academy where he is teaching courses on Programming Languages and Compilers, on High Performance Computing and on Advanced Shell programming. Prior to this he was writing software for some of the biggest and fastest computers in the world as a software engineer for Cray Inc. A software consultant, manager, analyst and programmer with an amazing breadth of software experience, Carl has worked with companies in the US, Canada and Europe. He has worked for large companies and small startups, in technical as well as in managerial and marketing roles. Carl's education includes a Ph.D. in Computer Science as well as an undergraduate degree in Mathematics and an International MBA. He has spoken at conferences and training seminars in the US, Canada and Europe as well as local high schools and colleges. Carl enjoys speaking at user groups and seminars on a variety of topics related to bash.
JP Vossen has been working with computers since the early 80s and has been in the IT industry since the early 90s, specializing in Information Security since the late 90s. He's been fascinated with scripting and automation since he first understood what an autoexec.bat was, and was delighted to discover the power and flexibility of bash and GNU on Linux in the mid-90s. He has previously written for Information Security Magazine and SearchSecurity.com, among others. On those few occasion when he's not in front of a computer, he is usually taking something apart, putting something together, or both.