If you are using Mac OS X and install Drush 9 and want to use MAMP for your development, you will need to do a bit of extra work to get it working.
If you do not have Drush 9 installed, see how to install it here https://suesdesign.co.uk/install-composer-and-drush-on-mac-os-x/. You will also need to start MAMP and have Drupal 8 installed. […]