waiting for process substitutions - redux

[Zachary Santer]

Was "Process substitution documentation request" on help-b...@gnu.org[1].

On Thu, Jun 25, 2026 at 6:29 PM Zachary Santer <zsan...@gmail.com> wrote:
>
> On Thu, Jun 25, 2026 at 7:32 AM Greg Wooledge <g...@wooledge.org> wrote:
> >
> > sudowrap() {
> >     local arg max=3
> >     for arg; do
> >         if [[ $arg =~ ^/dev/fd/([0-9]+)$ ]]; then
> >             max=$(( BASH_REMATCH[1]+1 > max ? BASH_REMATCH[1]+1 : max ))
> >         fi
> >     done
> >     sudo --close-from="$max" "$@"
> > }
>
> > hobbit:~$ sudowrap diff <(echo 1) <(echo 2)
>
> Alright, you win. And that's fairly simple to boot.

This just gave me an idea. Remember some time ago I was complaining
that there was no way to collect all the pids for the process
substitutions when more than one appears in a command, only to realize
that the new function substitutions could do it for you in every
case[2][3]?

Well, by golly! Who needs funsubs?

procsub-wait-solution-2:
```
#!/usr/bin/env bash

shopt -s lastpipe

main () {
  local -a -i wait_pids=()
  tee_three
  declare -p wait_pids
  wait -- "${wait_pids[@]}"
  declare -p SECONDS
}

tee_three () {
  tee_two >( declare -p BASHPID; sleep 15 )
}

tee_two () {
  wait_pids+=( "${!}" )
  tee_one "${@}" >( declare -p BASHPID; sleep 10 )
}

tee_one () {
  wait_pids+=( "${!}" )
  tee_zero "${@}" >( declare -p BASHPID; sleep 5 )
}

tee_zero () {
  wait_pids+=( "${!}" )
  printf '%s\n' {0..10} |
    tee "${@}" |
      sleep 2
  #
}

main
```

$ ./procsub-wait-solution-2
declare -i BASHPID="2006"
declare -i BASHPID="2007"
declare -i BASHPID="2008"
declare -ai wait_pids=([0]="2006" [1]="2007" [2]="2008")
declare -i SECONDS="15"

That's not convoluted at all! /s Works like a charm, though. And
considering that the function at the top of the call stack, in this
case tee_zero (), is just handling a bunch of filenames, no reason you
couldn't use those in redirections.

>From [4]:
On Fri, Jul 12, 2024 at 11:48 AM Chet Ramey <chet.ra...@case.edu> wrote:
>
> On 7/9/24 6:12 AM, Zachary Santer wrote:
> >
> > Maybe a single middle-ground array variable, listing the pids of all
> > child processes forked (and not waited on) since the last time the
> > array variable was referenced, would be more easily implemented.
>
> Maybe in some future version.

Chet... you know you want to...

Not about to promise a patch, but what would a good name for such a variable be?

[1] https://lists.gnu.org/archive/html/help-bash/2026-06/msg00045.html
[2] https://lists.gnu.org/archive/html/bug-bash/2024-10/msg00041.html
[3] https://lists.gnu.org/archive/html/bug-bash/2024-12/msg00128.html
[4] https://lists.gnu.org/archive/html/bug-bash/2024-07/msg00105.html