How to install extension for php via docker-php-ext-install?

Question

In order to resolve an issue, I am now trying install the mysql pdo via

docker-php-ext-install

as pointed out in the README of the php imag

Answer 1

RUN docker-php-ext-install mbstring pdo pdo_mysql \

That code can do install any extension you want in this case mysql pdp driver but the Dockerfile should have base of FROM php:7.1.8-apache