Interesting assortment, but quite a few items are out of date, and there's nothing to indicate quality.

For example, I took a look at the online "Ruby Essentials". Horrible. The section n variables is just wrong, and will leave people extremely puzzled about program behavior.

So much knowledge freely available. There's so much it's hard to know where to start looking. Anyone care to point out any books available through these links that they've found helpful? Aside from MIT's open courseware (which is generally awesome, esp. Intro to Algorithms), I'm not sure I've used any of these resources.

I just dug up a chapter on Bash scripting from an OReilly Open Book: http://oreilly.com/catalog/debian/chapter/book/ch13_01.html

GNU Make: http://oreilly.com/catalog/make3/book/index.csp

Just wanted to say thanks for the link--I've been searching for a legitimate ebook directory.

The MIT courseware and cheat sheets look very useful!

check out your local city and college library resources: e.g. Oreilly safari service in the San Francisco public libraries:

http://news.ycombinator.com/item?id=1327953

The Phoenix, AZ library gives access to books24x7.com.