$ curl -sS -o /dev/null -w '%{http_code}\n' http://127.0.0.1:18081/README.md
200
[exit 0]

$ curl -sS -o /dev/null -w '%{http_code}\n' 'http://[::1]:18081/README.md'
curl: (7) Failed to connect to ::1 port 18081 after <n> ms: Couldn't connect to server
000
[exit 7]