[GRASSLIST:5662] A r.shrink ?

[Soil & Water Lab.]

Hello,
Is there any such thing as a "r.shrink" command, that would work reverse from 
"r.grow" ? ie, from a given cellclump, to find the cells that are immediately 
on the border, or at a given distance from the border ?
I must admit that I can't find any simple script that would do this without 
much troubles (viz, without checking cells one by one...).
Thanks a lot for any input/insight
P.
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Soil and Water Laboratory
Biological and Environmental Engineering Department
Cornell University
Riley-Robb Hall
ITHACA, NY 14853 - USA