[luatex] os.execute v \write18

[David Carlisle]

Hans,

> so make a specific execute command and implement it different for different engines
> write18 was a strange animal anyway

Oh  for certain yes the \write18 emulation isn't designed as the ideal
interface going forward
but despite my plain tex example, as you might guess the real question
is latex and
20 or so years of legacy \write18 use.

The question we get asked all the time is how easy is it to take a
latex document and use lualatex.
so making it possible for things to work either with no change or just by adding
\usepackage{weirdwrite18hack}
is worth the effort of working out what those hacks should be, and how
far they may be expected to work.

I'm not surprised \immediate is weird in the internals it's pretty
weird in its public behaviour as well:-)

So I gather from your response that I haven't missed anything too much
so thanks for that, I'm sure we'll
be able to get something working. To be decided at what level any of
this kind of emulation is placed:
in the format, in an optional package, or just in documentation or
example code you could use.

Thanks again for the comments,

David