Re: Capture stdout, stdin, and exit status in different variables without using temporary files

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

I assume you meant stderr and not stdin which would make little
sense. And the bash wiki pages refers to capturing both stdout
and err, not stdin (whatever that means).

2019-08-15 20:22:38 +0430, Aryn Starr:
> If not, is a named pipe advantageous to a temporary file?

With named pipes, you'd get deadlocks unless you use a
select()/poll() loop like for unnamed pipes.

> Is there a way to avoid disk IO (which will probably slow things down considerably)?

To expand on the solution in the link I gave earlier to also
capture the exit status, that would be:

<<
#! /bin/zsh -
zmodload zsh/zselect
zmodload zsh/system

(){exec {wo}>$1 {ro}<$1} <(:) # like yash's wo>>|ro (but on Linux only)
(){exec {we}>$1 {re}<$1} <(:)

# the command (here ls as an example)
ls -d / /x >&$wo 2>&$we & pid=$!

exec {wo}>&- {we}>&-
out= err=
o_done=0 e_done=0

while ((! (o_done && e_done))) && zselect -A ready $ro $re; do
  if ((${#ready[$ro]})); then
    sysread -i $ro && out+=$REPLY || o_done=1
  fi
  if ((${#ready[$re]})); then
    sysread -i $re && err+=$REPLY || e_done=1
  fi
done
wait "$pid"; exit_status=$?

printf '%s: %s\n' stdout "$out" stderr "$err" 'exit status' "$exit_status"
>>

Which gives:

stdout: /

stderr: ls: cannot access '/x': No such file or directory

exit status: 2

(note that in $out and $err, the trailing newline character is
not removed).

-- 
Stephane