vpnclient_ynh/conf/scripts/route-up.d/20-set-ipv6

#!/bin/bash

source /usr/share/yunohost/helpers

is_ip6addr_set() {
  local ip6_addr=${1}
  ip address show dev tun0 2> /dev/null | grep -q "${ip6_addr}/"
}

ip6_addr=$(ynh_app_setting_get --app="vpnclient" --key="ip6_addr")
if [[ -n "${ip6_addr}" ]] && [[ "${ip6_addr}" != none ]] && ! is_ip6addr_set "${ip6_addr}"; then
  ip address add "${ip6_addr}/64" dev tun0
fi