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. As you peruse beginner-level Unix books and Web sites (see Appendix E), for example, you'll gradually become familiar with a few more important terms and tools.
Here's a rundown of some more cool (and very safe) programs that await your experimentation.
If you don't return to the $ prompt after using one of these commands, type q or, in some cases, quit, and then hit Enter.
Mac OS X and Windows aren't the only operating systems that come with a basic calculator accessory; Unix is well equipped in this regard, too.
When you type bc and hit Enter, you get a copyright notice and then…nothing. Just type the equation you want to solve, such as 2+2, or 95+97+456+2-65,or (2*3)+16595*(2.5*2.5), and then press Enter. On the next line, bc instantly displays the result of your calculation.
(In computer land, * designates multiplication and / represents division. Note, too, that bc solves equations correctly; it calculates multiplication and division before addition and subtraction, and inner parentheses before the outer ones. For more bc tricks and tips, type man bc at the prompt.)
Mac OS X offers no shortage of ways to cut the cord on a program that seems to be locked up or runnning amok. You can force quit it, use Activity Monitor, or use kill.