pnmdepth --version (return code: 0)
pnmdepth: Using libpbm from Netpbm Version: Netpbm 10.0
pnmdepth: BSD defined
pnmdepth: RGB_ENV='RGBDEF'
pnmdepth: RGBENV= 'RGBDEF' (env vbl is unset)
pnmdepth -h (return code: 1)
usage: pnmdepth newmaxval [pnmfile]