Running ngrok in the background

By default, ngrok launches an interactive session. This is great for local development, but not if we're using it in an automated fashion (e.g. in CI). We can use this method to run ngrok in the background, and to acquire the randomly generated public url:

# run ngrok in the background
ngrok http 80 --log=stdout >/dev/null &
# get the public url
PUBLIC_URL=$(curl -sS http://localhost:4040/api/tunnels | jq -r '.tunnels[0].public_url')

Source: ngrok/issues/57