Re: The primitiveness of pipe

[haahr@mv.us.adobe.com (Paul Haahr)]

> Imagine we had such a primitive, let's call it $&pipe2 so we don't
> confuse it with the current pipe primitive.  pipe2 would open a pipe
> and return the two resulting file descriptors.  It would also do the
> necessary internal book-keeping for the file descriptors.

> Then we should be able to rewrite %pipe in terms of $&pipe2 and
> $&background, at least in principle.  We may or may not want to do so.

getting everything right w.r.t. closing the pipe before waiting is
a little hard; i'm not sure that you wouldn't need some additional
hackery in wait, but it could probably be made to work.

> But we could also do all sorts of things you can usually not do in
> other shells, like open a file descriptor in the current shell which
> is a pipe into (or from) a process running in the background.

that's already pretty easy to do if you have /dev/fd, and is
easily simulated in most cases with the <{} and >{} implementations
using /tmp.  one case which does not work w/o /dev/fd but i like
very much is

	; exec {%open 0 <{echo foo; echo bar} {}}
	; cat
	foo
	bar
	; 

paul