xgamma -version (return code: 0)
xgamma 1.0.6
xgamma --help (return code: 1)
xgamma: unrecognized argument --help
usage: xgamma [-options]
where the available options are:
-display host:dpy or -d
-quiet or -q
-screen or -s
-version or -v
-gamma f.f Gamma Value
-rgamma f.f Red Gamma Value
-ggamma f.f Green Gamma Value
-bgamma f.f Blue Gamma Value
If no gamma is specified, returns the current setting