the "ripup" command has several forms:
ripup ; tears up all the routed tracks. (or click "ripup" followed by the traffic light.)
ripup signalName tears up a single signal.
ripup (click on trace) tears up the individual segment of the trace. Click on an airwire that is part of a signal, and it tears up the signal between nodes.
ripup (click on polygon border) un-fills the polygon.
BTW: EAGLE has an "undo" command that works really well, and will save you from a lot of mistakes.
It's a "User Language Program", which you can invoke with the "run" command.
It's a bit different than a script because the ULPs have access to the internal data structures.