Ruby In A Nutshell
Yukihiro Matsumoto
O'Reilly Media
I've lost track of the number of times in the first two chapters where I either read a sentence that had no clear meaning, or where I saw an example that was just plain incorrect.

Page 12: "A symbol is an object corresponding to an identifier or variable." Uh, what? That's the complete explanation for this language construct.

Page 64: "arr.slice(n, len) Deletes the partial string specified and returns it." Followed by an example obviously copied from String::slice on page 54, which has the exact same example code except using 's' instead of 'a'. But page 64 is supposed to be describing arrays, not strings, so the description and example are just plain wrong.

It goes on and on. I had high hopes for this book given my past experience with O'Reilly Nutshell books, but this book is just not ready to go to print yet, and obviously has been very poorly proofread. Sadly it's been printed and it's out there in the world, so your best bet is to just avoid it until O'Reilly publishes a 2nd edition that fixes all of these mistakes.