Re: The joy of pipes

On 2024-11-15, Louis Krupp <lkrupp@invalid.pssw.com.invalid> wrote:

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On 11/15/2024 12:49 AM, 186282@ud0s4.net wrote:

On 11/14/24 9:05 PM, Lawrence D'Oliveiro wrote:

On Thu, 14 Nov 2024 16:09:07 -0800, John Ames wrote:
>

(I think it was a topic shift to applications of *nix pipes...?)

>
Oh shelly boy, the pipes, the pipes are calling ...

>
  Pipes are good.
>
  But, really, they're just temp files the parent
  process can access.

>
Pipes *could* be implemented with temporary disk files, at least to an
extent, but as far as I can tell, they're not.
>
Quoting from this page:
>
https://www.geeksforgeeks.org/piping-in-unix-or-linux/#
>
    In Linux, a pipe is not a regular file but a type of inter-process
    communication (IPC) mechanism that acts as a buffer, which can be
    used to connect the output of one process to the input of another.
    Although pipes are not files, they are implemented using file
    descriptors and share many behaviors with files. They exist only in
    memory and do not have a presence in the file system, unlike regular
    files.
>
Louis

There are also "named pipes" aka FIFOs.  On Devuan Daedalus (and
probably most other distributions) this command will show
information about them:

        man 7 pipe

I have used a named pipe aka FIFO on a Raspberry PI.  An mplayer
process reads from a PVR-USB2 TV receiver and writes to the named
pipe or FIFO.  A netcat process reads from the named pipe or FIFO
to send the bits to a larger computer with substantial disk
storage.  A 105 minute recording session is several GB in size.
A cron job, ssh, and some shell scripting launch the stuff.

(Unfortunately, either the amplified TV antenna in the attic has
lost its gain, or the PVR-USB2 unit has lost front-end gain, so
it has not captured a viewable program in a few years.)

HTH

--
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)