[GRASS-user] measuring distance along a line

[Ronja Düffel]

Hi everybody,
is there a possibility to measure distance along a line in grass?
I have a map of a river system and I have points (given by Northing and 
Easting) where rivers con- or diverge. Now I would like know the distance 
between those points, measured along the course of the river. Is there a 
possibility to do that in grass without having to measure the distance by 
hand (i.e. using the measuring tool in the display window)?

I am using grass 6.2 on SuSE 10.2.

Help would be much appreciated,

Ronja