<<Anchor(faq108)>>
== How do I wait for several spawned processes? ==
There are numerous ways to do this, but all of them are either limited by the available tools.  I have come up with the following solutions.

If you want to wait for ''all'' your children, simply call `wait` with no arguments.

If you just want to wait for some, but not all, and don't care about their exit status, you can call `wait` with multiple PIDs:
{{{
wait $pid1 $pid2
}}}

If you need to know whether the children succeeded or failed, then perhaps:
{{{
waitall() { # PID...
  ## Wait for children to exit and indicate whether all exited with 0 status.
  local errors=0
  while :; do
    debug "Processes remaining: $*"
    for pid in "$@"; do
      shift
      if kill -0 "$pid" 2>/dev/null; then
        debug "$pid is still alive."
        set -- "$@" "$pid"
      elif wait "$pid"; then
        debug "$pid exited with zero exit status."
      else
        debug "$pid exited with non-zero exit status."
        ((++errors))
      fi
    done
    (("$#" > 0)) || break
    # TODO: how to interrupt this sleep when a child terminates?
    sleep ${WAITALL_DELAY:-1}
   done
  ((errors == 0))
}

debug() { echo "DEBUG: $*" >&2; }

pids=""
for t in 3 5 4; do
  sleep "$t" &
  pids="$pids $!"
done
waitall $pids
}}}

Looping through {{{kill -0}}} can be very inefficient.

More useful information might be found at [[ProcessManagement|Process Management]] page.