get pids of descendants processes of docker container and itself

docker_descendants_pids.sh

#!/bin/bash

# get docker container self and descendants pids
docker_container_pids=()
docker_container_descendants=()
for container_id in $(docker ps --format '{{.ID}}'); do
    a=$(docker inspect -f '{{.State.Pid}}' "$container_id")
    docker_container_pids+=( "$a" )
done
for pid in ${docker_container_pids[@]}; do
    for descendant in $(pstree -p $pid | grep -o '([0-9]\+)' | grep -o '[0-9]\+'); do
        docker_container_descendants+=( "$descendant" )
    done
done