[luatex] getting --output-directory

[Stephan Hennig]

Hi,

I want to read from and write to a particular file in --output-directory
or in the current directory, if option --output-directory is not used.

What is the preferred way in Lua to get the path set via option
--output-directory?  Is there an alternative to scanning table arg for
that option?  Some kpse library magic perhaps?

Best regards,
Stephan Hennig