For most people, the Mac's OS X is all about the graphical user interface. But system administrators and power users know that the Mac's command-line interface can be a powerful time saver and, in many cases, the only method to accomplish certain tasks. The command shell itself, delivered by Apple's included lTerminal program, is a wonder of open source. Bash -- for "Bourne again shell" -- was developed by free-software guru Brian Fox. It's widely used on operating systems of all kinds, including iOS, Linux, Unix, and mainframes. There's already a huge brain trust of tool knowledge around using Bash as a systems administrator's command shell.

But OS X brings its unique capabilities to the command-line table, in the form of utilities that leverage OS X's user interface, file system, and security capabilities. I've scoured the Internet for the best of the best of these utilities. Some you may already know, but others are sure to make you sit up and exclaim, "Sweet!"

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What follows is an alphabetical list of the 20 best command-line gems, with enough description to put you on the path to using their productivity riches. All commands, unless otherwise noted, run on all versions of OS X since 10.4 Tiger. For most of these commands, you can get more documentation using the "manpage" system: Type man followed by the command name. For example, man lsof displays the manual page for the List Open Files command.

1. airport : Scan your local wireless environment from the command line

When you click the Wi-Fi icon in OS X's menu bar (called AirPort before OS X Lion), you get a list of available wireless networks. The airport command-line utility does the same and a lot more. It shows you the numeric signal strength for every access point, the channel used, and the encryption level, if any.

Alas, the airport command-line utility is buried deep in the System directory (aka System folder when using OS X's GUI). But you can create a symbolic link to it using the one-time command below. Then just type airport -s in the Terminal's command line to get the detailed scan report. (Hint: If you don't get any output, turn Wi-Fi on in the Network system preference.)

To create a symbolic link to the airport command:

$ sudo ln -s /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport /usr/sbin/airport

To run a wireless scan:

$ airport -s

Sample results: