Actually, I wouldn't suggest either one as a tutorial.
"Programming Ruby" is a fine reference, but is a bit
terse as an introduction.  "Ruby in a Nutshell" is a
bit dated, but it is handy as a pocket reference.

I would recommend David Black's "Ruby for Rails".  In
fact, I'd love to see him extract a beginning Ruby book
from it, for folks who aren't planning to do Rails...

-r
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