g3topbm --version (return code: 0)
g3topbm: Using libpbm from Netpbm Version: Netpbm 10.0
g3topbm: BSD defined
g3topbm: RGB_ENV='RGBDEF'
g3topbm: RGBENV= 'RGBDEF' (env vbl is unset)
g3topbm -h (return code: 1)
usage: g3topbm [-kludge][-reversebits][-stretch] [g3file]