Manipulate Texture UVs with Shader

How can we manipulate a texture's UVs from a shader? I've taken a look at the [Shader Reference][1], but am still quite new to shaders and would like to be pointed in the right direction. Edit: Your help is greatly appreciated, sorry if the question was too vague. [1]: http://docs.unity3d.com/Documentation/Components/SL-Reference.html