How to export Camera UP-Vector

Hi there!
I'm working with paths and camera flight.
Now that I finished and my camera nicely moves along the path and rolls (by manually set keyframes), I need to export the whole data to a text file.

I already manage to get the camera position exported for every frame, as well as the target's position.

My problem is now: How to export (or just... "get") the camera's up vector, or the rotation coordinates, in order to export the camera roll?