Does it handle non-UTF8 filenames on Unix-like systems?

[vi]

Can it be used, for example, to pass entire command line array to a subprocess unmodified without restrictions, like xargs? Does it start from std::env::args (simpler, but makes this task impossible) or from std::env::args_os (proper way, but tricky)?

[Owez]

Currently the launch method uses std::env::args but i will consider transitioning into args_os as nothing too complex is done to strings other than strip_prefix

[vi]

nothing too complex is done to strings other than strip_prefix

It can still be somewhat tricky. You may want to review lexopt for how it's done.