> Actually, I am not sure how this would work.  If I do this, I get no output from the file:
>
> `tail -f sim.out`
>
> So there is something basic I am missing here.  Any help?

it shells out to the process and waits for it to return - with -f does
tail ever return? if not you may not be able to use it - AFAIK ` and
exec are the same - someone with better ruby knowledge may be able to
offer a solution - perhaps using threads or something

Kev