On Thu, Dec 5, 2024 at 2:13 PM Dan Cross wrote: > On Thu, Dec 5, 2024 at 3:56 PM wrote: > > Chet Ramey via TUHS wrote: > > > On 12/5/24 10:19 AM, Dan Cross wrote: > > > > > > > Unix pipelines, on the other hand, tend to be used in a manner that > is > > > > strictly linear, without the fan-out and fan-in capabilities > described > > > > by Morrison. Of course, nothing prevents one from building a > > > > Morrison-style "network" from Unix processes and pipes, though it's > > > > hard to see how that would work without something like `select`, > which > > > > didn't yet exist in 1978. Regardless, Unix still doesn't expose a > > > > particularly convenient syntax for expressing these sorts of > > > > constructions at the shell. > > > > > > Process substitution is about as close as we can get, but most programs > > > still process their filename arguments one at a time, beginning to end. > > > > > > The canonical process substitution example is > > > > > > diff <(old-program-version) <(new-program-version) > > > > > > to do simple regression testing. > > > > And fanout is simply > > > > ... | tee >(pipeline1) >(pipeline2) > > And indeed these things are pretty nifty, but don't they generate > trees, and not arbitrary dags? They don't quite capture the full > generality of Morrison-style networks since it doesn't seem like > there's a way to connect process substitution fan-out with fan-in; at > least, not conveniently. > > It is, perhaps, notable that Go allows me to do this sort of thing > with channels and goroutines, but it has `select` built into the > language. > > Funny, despite using Unix almost daily for over 30 years now, I don't > think I've ever felt limited by the power of pipelines. On the > contrary, I've lost count of the times I've felt limited on systems > that do Not support pipes. > The <() , >() syntax is a bash extension. Not all shells support it. And I couldn't find them in POSIX Issue 8. Warner