grdtrack(1gmt) on Linux
The text 18a29bd02d78, as Debian 4.0 (Etch) shipped it.
Sampling of a 2-D grdfile along 1-D trackline (a sequence of x,y points)
Flags it lists
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-: -
-G -
-H -
-L -
-M -
-Q -
-R -
-S -
-V -
-Z -
-bi -
-bo -
-f