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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.unix.shell
Subject: Re: Subjective "valuations" are all we have (Was: coprocs - again
 (Was: Different variable assignments))
Date: Fri, 25 Oct 2024 11:32:02 +0200
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On 25.10.2024 10:10, Kenny McCormack wrote:
> In article <vff8qc$31tk9$1@dont-email.me>,
> Janis Papanagnou  <janis_papanagnou+ng@hotmail.com> wrote:
> ...
>> For multiple co-processes you may be right. (I certainly differ
>> given how Bash implemented it, with all the question that arise.)
>> And I already said: I don't think it makes much sense to discuss
>> subjective valuations.
> 
> Our opinions are all we have.  I can't see how that can be "off topic".

Oh, don't get me wrong; to each his own [opinion]. That's fine.

It's certainly also not off-topic, but it's just opinion. Though the
other poster also didn't provide any examples or rationales for his
opinion - which is not surprising if you know him - where I tried to
explain my POV; whether you support it or disagree to.

I can extend on what I already hinted upthread...

> [...]
> 
> I really do think that there's no significant difference in verbosity
> between the two implementations (certainly in the simple case). 

Verbosity was not my point. (Only that I was repelled by the other
poster's, as far as I understand, unnecessary ballast in his code.)

But clearness or fitting into existing shell concepts do matter, IMO.

> The ksh
> way of handling multiples looks kludgey to me (you may think otherwise, of
> course).  It certainly looks to me that the bash way was designed (no doubt
> benefiting from ksh having paved the way), whereas the ksh way "just grew".

Well, the Bash way looks quite "hacky" in my opinion. But maybe you
could explain what I might have missed. The questions I'd have are
(for example); [from the bash man page] in

  coproc [NAME] command [redirections]

what is the 'coproc' actually (beyond a "reserved word")? Is it a
shell construct like, say, a 'case' construct, or a command, like,
say, 'pty' or 'time'? Then, depending on that; is the redirection
part of a special case here? And that's the reason why it's listed
explicitly? Note redirection is an orthogonal concept! Here too?
The access to the FDs is implicitly defined by 'COPROC[0]' for
"output" to the process and 'COPROC[1]' for input to the process;
is this coherent with 'stdin'(0) and 'stdout'(1); this at least
irritates me, it's not as obvious as it could be.

In Ksh I have the simple case that you can simply use

  command |&

  print -p
  read -p

Easy to use, clear, no ballast, no questions [to me].

If you want to redirect it with explicit FD control you use Ksh's

  exec 3<&p 4>&p

(and then 'read -u3' and 'print -u4' to communicate) for example.

Or you want Ksh to choose the FDs, then use variables (as you can
also generally do with non-coprocess related redirections) like

  exec {IN}<&p {OUT}>&p

(with arbitrary variable names, here IN and OUT chosen, which looks
more sophisticated to me than 'COPROC[0]' and 'COPROC[1]'). And you
can use the variables then simply as you're used to from other cases

  print -u $OUT
  read -u $IN

This fits well in Ksh's redirection feature set. And I suppose Bash
does not support FD variables, since the 'COPROC' (or own variables)
in this specific ("hacky") context needs to be introduced? - Or am I
mistaken that this is a 'coproc'-specific hack? - Bash's construct
[to me] looks flange-mounted (hope that is the correct word to use).

This post should also explain why I think that your valuation that
in Ksh the feature "just grew" is not justified. Beyond the '|&' vs.
'coproc' reserved word; consistency with '|' and '&', redirection,
assigned FDs (if desired), consistent 'p' as read/print option and
as FD, all fits and allows for readable straightforward code in Ksh
that also doesn't leave me with questions.

BTW, co-processes were designed into the shell with Ksh88 already;
not much to "just grow" (as you insinuated). ;-)

Janis

> [...]