psmask(1gmt) on Linux
The text 73729ce374fd, as Debian 7 (Wheezy), Debian 5.0 (Lenny), Debian 3.1 (Sarge) shipped it.
To clip or mask areas of no data on a map
Flags it lists
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-: -
-B -
-C -
-D -
-E -
-F -
-G -
-H -
-I -
-J -
-K -
-M -
-N -
-P -
-R -
-S -
-T -
-U -
-V -
-X -
-Y -
-bi -
-bo -
-c