In the common case, you can write the long-form help output typical of a modern
command line program, and let this module generate a custom parser that collects
and diagnoses the options it describes.

The parser is actually an object instance which can then be tweaked for the
uncommon case, by hand, or by using the "on" method to tie your custom handlers
to options that are not handled quite the way you'd like.

This is a pure Lua library compatible with LuaJIT, Lua 5.1, 5.2, 5.3, 5.4 and
5.5.