understand extra pair of trap and wait

https://stackoverflow.com/questions/49489948/why-an-extra-pair-of-trap-and-wait

============

test.sh

============

#!/bin/bash

_term() {

  echo "SHELL: Caught SIGTERM signal, propagating to the child"

  kill -TERM "$child" 2>/dev/null

}

trap _term SIGTERM

python3 test.py &

child=$!

wait "$child"

exit_status=$?

trap - SIGTERM

wait "$child"

if test ${exit_status} -eq 0; then

  echo "SHELL: Task finished.";

else

  echo "SHELL: Task failed.";

  exit ${exit_status}

fi

============

test.py

============

import time

import sys

import signal

import time

class GracefulKiller:

  kill_now = False

  def __init__(self):

    signal.signal(signal.SIGINT, self.exit_gracefully)

    signal.signal(signal.SIGTERM, self.exit_gracefully)

  def exit_gracefully(self,signum, frame):

    self.kill_now = True

if __name__ == '__main__':

  killer = GracefulKiller()

  while True:

    print("== going to sleep ==")

    time.sleep(30)

    print("== woken up ==")

    if killer.kill_now:

      break

  print("End of the program. I was killed gracefully :)")

--

Rahul Gupta