This one is a back-to-the-basics for UNIX/Linux/*nix lovers. The command-line is probably one of UNIX's most popular user-facing feature. So much so that this love has grown over to the windows and Mac OS users as well. Even todays most sophisticated browsers like Firefox have command-line support in the form of extensions like Ubiquity and Vimperator.
Anyway, here's a nice article about the various characters used in the UNIX command line, for example, |$#@ and so on. It covers each character with a nice example.
See also: UNIX Interview Questions and my other UNIX/Linux related articles.