rgb3toppm --version (return code: 0)
rgb3toppm: Using libpbm from Netpbm Version: Netpbm 10.0
rgb3toppm: BSD defined
rgb3toppm: RGB_ENV='RGBDEF'
rgb3toppm: RGBENV= 'RGBDEF' (env vbl is unset)
rgb3toppm -h (return code: 1)
usage: rgb3toppm <red pgmfile> <green pgmfile> <blue pgmfile>