用法:
<pre class="brush:cpp ;toolbar: true; auto-links: false;">$ racket l++.rkt -h
l++.rkt [ <option> ... ] [<filenames>] ...
where <option> is one of
-c, --compile : Compile only; do not run
-v, --verbose : Display verbose messages
-o <file> : Place the output into <file>
--help, -h : Show this help
-- : Do not treat any remaining argument as a switch (at this level)
Multiple single-letter switches can be combined after one `-'; for example: `-h-' is the same as `-h --'</pre>