Problem setting security key when installing Craft 3
Add this line to your ~/.bash_profile file

export PATH="/Applications/MAMP/Library/bin:/Applications/MAMP/bin/php/php7.0.0/bin:${PATH}"


Assuming your php7 version in mamp is 7.0.0 of course.

Here is a link with a few more steps if you aren't sure how to edit that file - https://gist.github.com/irazasyed/5987693