Fixing Bug laradock#1017

environment variables were removed from

mysql/Dockerfile

@@ -12,8 +12,24 @@ RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
 
 RUN chown -R mysql:root /var/lib/mysql/
 
+ADD startup /etc/mysql/startup
+
+ARG MYSQL_DATABASE=default
+ARG MYSQL_USER=default
+ARG MYSQL_PASSWORD=secret
+ARG MYSQL_ROOT_PASSWORD=root
+
+ENV MYSQL_DATABASE=$MYSQL_DATABASE
+ENV MYSQL_USER=$MYSQL_USER
+ENV MYSQL_PASSWORD=$MYSQL_PASSWORD
+ENV MYSQL_ROOT_PASSWORD=$MYSQL_ROOT_PASSWORD
+
+RUN sed -i 's/MYSQL_DATABASE/'$MYSQL_DATABASE'/g' /etc/mysql/startup && \
+    sed -i 's/MYSQL_USER/'$MYSQL_USER'/g' /etc/mysql/startup && \
+    sed -i 's/MYSQL_PASSWORD/'$MYSQL_PASSWORD'/g' /etc/mysql/startup
+
 ADD my.cnf /etc/mysql/conf.d/my.cnf
 
-CMD ["mysqld"]
+CMD ["mysqld", "--init-file=/etc/mysql/startup"]
 
 EXPOSE 3306