Note: help and version output are generated by a naïve script which tries a few variants of
<command> --help, <command> -h etc. to find the command's help and version info.
Sometimes it gets lucky, sometimes it doesn't; if the output below looks wrong, it probably is.
ppm3d --version (return code: 0)
ppm3d: Using libpbm from Netpbm Version: Netpbm 10.0
ppm3d: BSD defined
ppm3d: RGBENV= 'RGBDEF' (env vbl is unset)
ppm3d -h (return code: 1)
usage: ppm3d leftppmfile rightppmfile [horizontal_offset]