Parallel job execution and aggregated exit status with Bash

README.md

The idea is from https://unix.stackexchange.com/questions/344360/collect-exit-codes-of-parallel-background-processes-sub-shells#436932

$ ./main.sh 5
[Task 4] Job starting...
[Task 4] Sleeping...
[Task 1] Job starting...
[Task 1] Sleeping...
[Task 2] Job starting...
[Task 2] Sleeping...
[Task 5] Job starting...
[Task 5] Sleeping...
[Task 3] Job starting...
[Task 3] Sleeping...
[Task 5] Successfully completed
[Task 1] Successfully completed
[Task 2] Successfully completed
[Task 3] Something went wrong!
[Task 4] Successfully completed

$ echo $?
1

As the outputs from sub tasks are prefixed with task IDs, you can easily filter to check only particular task's output:

$ ./main.sh 5 | grep '^\[Task 3\] '
[Task 3] Job starting...
[Task 3] Sleeping...
[Task 3] Something went wrong!

Or group the output by tasks

$ ./main.sh 5 | sort -s -n -t' ' -k 2,2
[Task 1] Job starting...
[Task 1] Sleeping...
[Task 1] Successfully completed
[Task 2] Job starting...
...

main.sh

#!/usr/bin/env bash

set -euo pipefail

readonly num_of_tasks=${1:-4}

pids=()

for i in $(seq 1 "$num_of_tasks") ; do
    { ./sub-task.sh "$i" 2>&1 | sed "s/^/[Task $i] / " ; } &
    pids+=("$!")
done

overall_exit_code=0
for p in "${pids[@]}"; do
    wait "$p" || overall_exit_code=$((overall_exit_code + $?))
done

exit $overall_exit_code

sub-task.sh

#!/usr/bin/env bash

set -euo pipefail

task_id="$1"

echo "Job starting..."

sleep_sec="$((task_id % 5))"

echo 'Sleeping...'
sleep "$sleep_sec"

if [[ "$sleep_sec" = 3 ]] ; then
    echo 'Something went wrong!' 1>&2
    exit 1
fi

echo 'Successfully completed'