support ipv4|[ipv6]|domain:port; fix Alpine grep P

(cherry picked from commit 1fde0ad)

Author: thohng

root/etc/cont-init.d/50-config

@@ -56,8 +56,9 @@ if ! grep -Fxq "APP_KEY=${key}" /config/www/.env; then
     sed -i "s#^APP_KEY=.*#APP_KEY=${key}#" /config/www/.env
 fi
 
-# if DB_HOST contains a port
-if echo "${DB_HOST}" | grep -qP '^(?:[0-9.]+|(?:\[[0-9a-fA-F:]+\]))(:[0-9]+)$'; then
+# if DB_HOST contains a port and DB_HOST is not a IPv6 without brackets [..]
+# support ipv4:port, [ipv6]:port, and domain:port
+if echo "$DB_HOST" | grep -qE ':[0-9]+$' && ! echo "$DB_HOST" | grep -qE '^(:{0,2}[a-fA-F0-9]{1,4})+$'; then
     DB_HOST_PORT="${DB_HOST}"
 fi