How do I upgrade PHP in Mac OS X?

Question

I feel this is an awfully obtuse question to ask, but strangely, this problem is poorly documented.

I would like to upgrade PHP, but there are several problems:

Answer 1

Saving on keystrokes, this worked on MacOS Sierra:

$ brew install homebrew/php/php71

$ /usr/local/opt/php71/bin/php -v
PHP 7.1.4 (cli) (built: Apr 14 2017 15:02:16) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies