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From: pete@violet.berkeley.edu (Pete Goodeve)
Newsgroups: comp.sys.amiga.tech
Subject: Re: PIPEs
Summary: "Fan-out" pipes
Message-ID: <1990Nov10.082242.22949@agate.berkeley.edu>
Date: 10 Nov 90 08:22:42 GMT
References: <2641@mtecv2.mty.itesm.mx> <7005@sugar.hackercorp.com> <1990Nov8.101107.5884@zorch.SF-Bay.ORG>
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In  <1990Nov8.101107.5884@zorch.SF-Bay.ORG>,
Kent Paul Dolan (xanthian@zorch.SF-Bay.ORG) writes:
>
> I like the "+" convention, but I'd rather use "-<" and ">-" with it, so
> that I could say:
>
>             cmda args -<{1,2}   +
>             cmdb args -<{1,2,3} +
|             >-1 cmdc args -<2       +
|             >-2 cmdd args -<4       +
|             >-3 cmde args -<1       +
|             >-4 cmdf args           > result
>
> and have cheap to type, multiple input, multiple output "named" pipes,
> [....]
>
> This would be a nice syntax for Pete Goodeve's pipe mechanism (which
> does its interleave synchronization at the message-full level) when he
> gets the fan-out side working to go along with the fan-in side.
>
Hmmm.  What an interesting idea...  In fact it gets more intriguing as I
think on it.  "Fan out pipes" are something that even unix can't do, as
far as I can see.  (You can 'tee' to a pipe and a file, but not to two
parallel pipes, can you?)  And a convenient way of "broadcasting" data to a
number of processes is something that I've had on my mind for a long, long
time.

Kent's scheme might need a fair amount of "thinking" on the part of the
shell -- or 'pipe' program if that was the way it was done (in fact, with
the '+' termiator, it could easily be a separate program) -- because
several fan-out processes might have to be started.  Could be done, though.

My immediate intentions ["immediate" - hah! I've just been sitting on it for
about three months...] were to make a simple 'ITEE' program, that would
take one input (ppipc) stream, and distribute copies of this to as many
outputs as you had specified in the command line.  I guess you could
have the 'pipe' command start copies of this -- or some variant -- as
necessary.

I've been thinking about the convention that Kent suggests, though, and
I wonder if it wouldn't be better to reverse it:

             PIPE cmda args >-{1,2}  +
             cmdb args >-{1,2,3}     +
             -<1 cmdc args >-2       +
             -<2 cmdd args >-4       +
             -<3 cmde args >-1       +
             -<4 cmdf args > result

This isn't much worse (to my eye!) in appearance that the other, but
a) it does not conflict with standard redirection direction (:-)), and
b) it makes command line parsing MUCH easier, because you're already
looking for the '>' redirection character. Special sequences at the
BEGINNING of a line are always easy to find.  Of course you'd have to avoid
file names beginning with '-'...

In fact there are LOTS of variants one could consider. I suppose once could
make the convention EXACTLY equivalent to the current one, with redirection
in the standard AmigaDOS place after the command.  Or you might use the
pairs '|<' and '>|'.

Whatever, it's worth thinking on.

                                    -- Pete --