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

[John Cowan]

There was no concurrency in mini-Unix; the first pipeline component ran to
completion, and when it exited the next component ran, and so on.  In this
way a pipeline could be arbitrarily long using just two disk files.

On Thu, Dec 5, 2024, 12:07 PM Marc Rochkind <mrochkind at gmail.com> wrote:

> 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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