Re: coproc or whatever in bash and ksh (Was: Different variable assignments)

In article <vf0dn6$3t9fe$1@dont-email.me>,
Janis Papanagnou  <janis_papanagnou+ng@hotmail.com> wrote:

On 19.10.2024 15:35, Kenny McCormack wrote:

In article <vf0a1h$3sn0s$1@dont-email.me>,
Janis Papanagnou  <janis_papanagnou+ng@hotmail.com> wrote:

On 19.10.2024 13:45, Kenny McCormack wrote:

In article <vec3qb$3q4ms$3@dont-email.me>,
Lawrence D'Oliveiro  <ldo@nz.invalid> wrote:

On Fri, 11 Oct 2024 22:50:10 +0200, Frank Winkler wrote:
>

... but it still doesn't solve the issue that I need the result to be
visible in the parent shell.

>
   coproc { uname -sr; }
   read -u ${COPROC[0]} var3
   wait $COPROC_PID
   echo $var3

>
I'm actually a fan of "coproc" in bash, and I use it in my scripting,
but I think it is overkill in most cases.  [...]

>
Also, if above code is how to use co-processes in Bash, I consider
that extremely clumsy (if compared to, say, Ksh).
>
(Mileages may vary, of course.)

 
I think he was being intentionally verbose for pedagogic purposes.
 
I won't bore you with the details, but obviously a lot of the text in the
quoted 4 lines is unnecessary in practice.
 
Just out of curiosity, how would you (Janis) do this in ksh?

>
For the question on topic I wouldn't (as you wouldn't, IIUC) use
co-processes in the first place - even if [in ksh] we don't need
file descriptor numbers from arrays (like in the bash sample).

Agreed.

I'd use one of the one-liner solutions if I hadn't the "lastpipe"
functionality built-in or available. It also makes no sense, IMO,
to use co-processes that just read a simple value from a command.

Agreed.

Co-processes I have to use only rarely, and the applications are
from commands that provide some "service"; I send a request, and
then I retrieve the response (and rinse repeat, as they say).

Agreed.

The syntax for the [unnecessary] co-process application depicted
above would in Ksh be
>
 uname -sr |&
 read -p var
 echo "$var"

Which is pretty much the same as in bash, which would be:

    coproc { uname -sr; }
    read -u$COPROC
    echo "$REPLY"

Note that bash can be compiled to support multiple concurrent coprocs. (*)
Thus, it makes sense to have to explicitly specify the fd to read or write,
rather than (AIUI), in ksh where there is just "the coproc".

The multi-coproc feature is off by default (in bash), but can be turned on
by setting an option in one of the config.h files and re-compiling bash.
It is considered "experimental", but seems to work OK as far as I can tell.

(*) You do this by giving the 2nd and subsequent coprocs names and then use
that name instead of the default "COPROC" to access the I/O fds.

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