By far, the quickest and easiest way of installing Drush is via Homebrew. If you don’t already have Homebrew installed you can use the link above to find out more or just paste the below into the terminal.
Before installing Drush you may first have to install Git.
You can check Drush is ready to use by typing drush in the terminal and you’ll see a list of the available commands. Almost there but you will need to make sure that Drush uses the MAMP mysql.sock file.
Finally, you will need to add the MAMP bin folder added to your $PATH. You can do this by adding the following line to your .bash_profile
You can tell drush to use a specific PHP executable by setting the variable DRUSH_PHP