[TUHS] Pipes (was Re: After 50 years, what has the Impact of Unix been?)

[Marc Rochkind]

I don't think files as pipes would be "transparent to the user." Reading an
empty pipe causes a wait until the bytes requested are available, unless
the pipe is closed first. Reading to the end of a file results in an
end-of-file error. This problem is avoided if the source process completes
before the target process begins, but then there is a different lack of
transparency, which is that the processes don't run simultaneously. (I
think this is the case with the implementation that Heinz showed.)

Still, the same sort of pseudo-pipes were in MS-DOS, and they were
occasionally useful.

Marc

On Thu, Dec 5, 2024 at 9:17 AM Heinz Lycklama <heinz at osta.com> wrote:

> John, thanks for the reminder of the implementation
> of pipes on a constrained version of UNIX in the early
> days. The exact implementation is described on page 2095
> of the BSTJ July-Aug 1978 for interested parties.
>
>
>
> Heinz
>
> On 12/5/2024 8:00 AM, John R Levine wrote:
>
> On Thu, 5 Dec 2024, Dan Cross wrote:
>
> Pipes were invented at least three times I'm aware of, but what made them
> work so well in Unix is that they looked to the program the same as a file
> so any program could use them for input or output without special
> arrangements,
> and the shell made it easy to start two programs and pipe them together.
>
>
> Once you have coroutines and queues for passing data between them, a
> lot of things start to look like pipes.
>
>
> They also can look a lot like temporary files.  Someone, probably Heinz,
> did a shell for the tiny Unix that ran on floppies so this
>
>  foo | bar
>
> actually did this
>
>  foo > tmpfile ; bar < tmpfile; rm tmpfile
>
> to avoid having to swap programs in and out on floppies.  The main
> disadvantage was that the tmpfile could overflow the tiny disks of the
> time.
>
> They were invented again at IBM in the 1970s and described in this paper.
> I wrote
> them a letter, which they published, saying that Unix pipes did the same
> thing.
>
> https://dl.acm.org/doi/10.1147/sj.174.0383
>
>
> Don't forget CMS pipelines, too!
>
> Sadly, the Morrison paper cited above is not easily accessible, though
>
>
> If anyone else needs a copy, just ask.
>
> Regards,
> John Levine, johnl at taugh.com, Taughannock Networks, Trumansburg NY
> Please consider the environment before reading this e-mail. https://jl.ly
>
>
>

-- 
*My new email address is mrochkind at gmail.com <mrochkind at gmail.com>*
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