Mac: We love the command line for its power and speed, but if you make a mistake in a lengthy command, editing can be fiddly. If you want to wipe out everything you typed and start again, you can clear what you typed with a simple keyboard shortcut: Control+U.
When you press those keys, the entire line goes away. It's a simple tip many readers may already know, but it's a very useful one. Without it, you'd have to sit and press the delete key until every individual character disappeared.
6 Mac OS X Terminal Tips [Colmjude]