grdgradient(1gmt) on Linux
The text 85ca1105bb4d, as Debian 7 (Wheezy) shipped it.
Compute directional derivative or gradient from 2-D grid file representing z(x,y)
Flags it lists
-
-A -
-D -
-E -
-G -
-L -
-M -
-N -
-S -
-V