The running example throughout the book is to build an address book program called "rolo" (Rolodex, get it?), and the authors do a nice job of progressively building the features while illustrating useful techniques that are generally applicable.
I've not read the 3rd edition, but I can vouch for the fact that the 2nd would be getting a little dated by now. Still, it's well-written, well-structured, and a great introduction to most of the shell concepts that you use.
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