pgrep -P, but for grandchildren not just children

Question

I am using:

pgrep -P $$

to get the child pids of $$. But I actually want a list of grandchildren and great grandchild too.

How do I

Answer 1

The code below will print the PIDs of the current process and all its descendants. It uses a Bash array as a queue to implement a breadth-first search of the process tree.

unprocessed_pids=( $$ )
while (( ${#unprocessed_pids[@]} > 0 )) ; do
    pid=${unprocessed_pids[0]}                      # Get first elem.
    echo "$pid"
    unprocessed_pids=( "${unprocessed_pids[@]:1}" ) # Remove first elem.
    unprocessed_pids+=( $(pgrep -P $pid) )          # Add child pids
done