APL

How do I learn it?

Specifically: is there a good book I can get online, and a Linux implementation that won't make me blow my brains out?

You might want to get J. It's non-dead ASCII APL; instead of having a lot of weird symbols you can modify symbols by placing . or : behind them.

http://www.jsoftware.com/stable.htm
http://www.jsoftware.com/help/learning/contents.htm

It's still unreadable as shit and incredibly terse. 2|!/~i.32 is a Sierpinski triangle.