Find child processes (and their children, etc.) with one ps call (no race conditions)

pidtree.sh

#!/bin/bash

# Original idea: http://superuser.com/a/784102/59125

pidtree(){
  pids_for_ppid=()
  while read pid ppid; do
    pids_for_ppid[$ppid]+=" $pid"
  done < <(ps -e -o pid,ppid --no-headers)

  print_children(){
    for i in ${pids_for_ppid[$1]}; do
      ( (print_children $i) )
      echo $i
    done
  }
  ( (print_children $1) )
  echo $1
}

pidtree $1