So far, you've read about only a handful of the hundreds of Unix programs that are built into Mac OS X and ready to run. Yes, ls and sudo are very useful tools, but they're only the beginning. Here's a rundown of some more cool (and very safe) programs that await your experimentation.
Tip:
If you don't return to the $ prompt after using one of these commands, type q or, in some cases, quit; then hit Enter.