[TUHS] Excise process from a pipe

Larry McVoy lm at mcvoy.com
Fri Jul 11 00:45:03 AEST 2014

I'm pretty aware of the various flavors of Unix and unless the process 
in question is willing to help I can't see how this could work.

There are system calls for passing file descriptors but you have the 
problem that the pipe itself is a buffer of some size and you'd have
the problem of draining it.

Every utility that you put in a pipeline would have to be reworked
to pass file descriptors around, it would be really unpleasant and
not at all Unix like.

On Thu, Jul 10, 2014 at 08:04:43AM -0400, Doug McIlroy wrote:
> In the suggested answer, the code changes but the process survives.
> I suspect the answer to my original question is no, but I know only a tiny
> fraction of the cumulative API of the extended Unix family.
> Doug
> >> Was there ever a
> >> flavor of Unix in which a process could excise itself
> >> from a pipeline without breaking the pipeline?
> >
> > If in the middle of a pipeline, all I can think of is:
> >
> >       close fd 0 and fd 1
> >       dup() read end of pipe 1 to be stdin (fd 0)
> >       dup() write end of pipe 2 to be stdout (fd 1)
> >       exec("/bin/cat")
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Larry McVoy            	     lm at mcvoy.com             http://www.mcvoy.com/lm 

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