Ping pong of a signal between 2 processes - bash

Question

I want to write 2 scripts that send a signal each other, like a ping-pong match, but with a signal, not a ball.
First script:
#!/bin/bash
PATH=${PATH}:"/home/cosimo/Università/Sistemi Operativi/scripts"
exec player2pp.sh $$ &
trap "kill -SIGUSR1 $pidp2" SIGUSR1
sleep 2
Second script (player2pp.sh):
#!/bin/bash
trap "kill -SIGUSR1 $1" SIGUSR1
sleep 2
kill -SIGUSR1 $1
sleep 2
I got this error in player2pp.sh:
kill: no corresponding process.
What am I doing wrong?

Answer 1

Some problems:
you're launching the player2 script in the background, so you don't need exec
you don't store the PID of the player2 process anywhere
the first script launches player2, sleeps, then exits. You need to start some kind of infinite loop to avoid exiting.
if you kill the first script with Ctrl-C, the second script is left running in the background
Additionally, I would write a function for the trap so it's easier to do some logging:
player1pp.sh
#!/bin/bash
cd "/home/cosimo/Università/Sistemi Operativi/scripts"
./player2pp.sh $$ &
pidp2=$!
_ping() {
echo "ping! killing $pidp2"
kill -SIGUSR1 $pidp2
}
trap _ping SIGUSR1
trap "kill $pidp2" EXIT
while true; do sleep 2; done
player2pp.sh
#!/bin/bash
pidp1=$1
_pong() {
echo "pong! killing $pidp1"
kill -SIGUSR1 $pidp1
}
trap _pong SIGUSR1
_pong # start the game
while true; do sleep 2; done
For fun, add some randomness:
Player 1
#!/bin/bash
cd "/home/cosimo/Università/Sistemi Operativi/scripts"
./player2pp.sh $$ &
opponent=$!
ping() {
sleep=$((RANDOM % 5))
echo "ping! killing $opponent in $sleep"
sleep $sleep
kill -USR1 $opponent
}
trap ping USR2
cleanup () {
kill -0 $opponent && kill $opponent
}
trap cleanup EXIT
ping
while :; do :; done
Player 2
#!/bin/bash
opponent=$1
pong() {
sleep=$((RANDOM % 5))
echo "pong! killing $opponent in $sleep"
sleep $sleep
kill -USR2 $opponent
}
trap pong USR1
cleanup () {
kill -0 $opponent && kill $opponent
}
trap cleanup EXIT
while :; do :; done