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@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly