ngrok running in background
as explained here
ngrok -log=stdout 80 > /dev/null &
as described previously you can run ngrok in background with
./ngrok http 8080 > /dev/null &
next you can use curl and for example jq
a command-line JSON processor.
export WEBHOOK_URL="$(curl http://localhost:4040/api/tunnels | jq ".tunnels[0].public_url")"
your URL will be accessible from $WEBHOOK_URL env variable and you can use it anywhere.
Visit http://localhost:4040/status on your local machine, or see more here: View random ngrok URL when run in background.