grdgradient(1) on Linux
The text 0bf3239c77b2, as Debian 2.2 (Potato) shipped it.
Compute directional derivative or gradient from 2-D grd file representing z(x,y)
Flags it lists
-
-A -
-D -
-G -
-L -
-M -
-N -
-S -
-V