Telling Ubuntu 16 to use a different PHP version on cli
When you have multiple versions of PHP installed things can get a bit wonky. PHP 7.1 has broken a lot, and I've noticed most LAMP apps and a lot of commandline tools such as Drush just aren't compatible yet.
With Nginx, it makes it easy to run your sites on a specific PHP version like 7.0, but if you install 7.1 on your server you might want cli applications to use 7.0 still.