Re: questions about coproc

[Chet Ramey]

On 3/9/23 1:47 PM, Britton Kerin wrote:
> First let me say coproc is quite nifty, thanks for implementing!
>
> One thing I've done is make a small regex server for bash using perl:
>
> coproc perl_regex_server {
>    perl <(cat <<'  END_PERL'
>      use strict; use warnings;
>      $| = 1;
>      while ( 1 ) {
>        my $rex = <>;
>        chomp($rex);
>        my $str = <>;
>        if ( $str =~ m/$rex/ ) {
>          # FIXME: Sadly this die argument doesn't show anywhere:
>          defined($1) or die 'group $1 unexpectedly undefined';
>          print length($1);
>        }
>        print "\n";
>      }
>    END_PERL
>    )
> }
>
> It works great for my intended purpose (smarter word movement for
> ble.sh), with the only issues being:
>
> 1.  no obvious way to propagate e.g. the die argument in the above
> back to the controlling terminal.  Is there some easy way to do this
> that I missed?

Coprocs don't modify stderr, so if you write to stderr it will get to
wherever the calling shell has directed it.

> 2.  If the above job has been created from e.g. ~/.bashrc, then when I
> try to make another coproc I get an error like this on the terminal:
>
>       bash: warning: execute_coproc: coproc [11142:perl_regex_server]
> still exists
>
> The new coproc seems to exist and work, but this error is worrisome
> and would be very confusing to a user who wasn't aware of this coproc.
By default (there is a compile-time option to change it), the shell only
keeps track of a single coproc.

This means that it will reap the coproc when it dies, since it's a child
of the shell, but not unset any of the associated variables or ensure the
pipe file descriptors are closed in the parent.

> 3.  I don't really like seeing it as a job in job control.  I wonder
> if it might be appropriate to have an option to hide from the job
> control list, or hide unless some option to jobs is given. 

It is a job, since it's executed as if the command had been terminated
with `&'. If you don't want to see it, use `disown'; that's the general
mechanism for doing this.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/