bash process synching

#!/bin/bash

set -e

sleep 10
echo "crash"
exit 1

#!/bin/bash

set -e

while true
do
    echo hello world
    sleep 1
done;

#!/bin/bash

set -e

trap "exit" INT TERM
trap "kill 0;" EXIT

./test2.sh &
PID1=$!

./test3.sh &
PID2=$!

export PID1 PID2
( tail -f --pid=$PID1 /dev/null; kill $PID2; ) &
( tail -f --pid=$PID2 /dev/null; kill $PID1; ) &

wait -n 

#!/bin/bash

set -e

kill_foreground() {
    echo "Background script has finished. Killing foreground script."
    ps -C "test3.sh" -o "%p"| grep -v PID | xargs kill;
}

kill_background() {
    echo "Foreground script finished. Killing background script."
    kill 0;
}


trap "exit" INT TERM
trap "kill_background" EXIT

./test2.sh &

export PID1=$!
( tail -f --pid=$PID1 /dev/null; echo "kill test3.sh "; kill_foreground ) &

./test3.sh