CLEF is a Command Line Extension Finder. Well, actually is nothing more than a bunch of lines utilizing curl + pcre to parse the extension repository and send back the results.
With CLEF you can search, get information and download any of the extensions hosted in the official Yii repository (http://www.yiiframework.com/extensions).
Place the php file you'll find in the zip under protected/commands
Get the updated usage by calling:
yiic help clef
Bugs & feature requests can be filed @ the github page.