使用命令安裝PHP5.6：brew install php56
之後根據命令列的提示進行設定環境變數

✩✩✩✩ Extensions ✩✩✩✩

If you are having issues with custom extension compiling, ensure that you are using the brew version, by placing /usr/local/bin before /usr/sbin in your PATH:

      PATH="/usr/local/bin:$PATH"

PHP56 Extensions will always be compiled against
 
 this PHP. Please install them using --without-homebrew-php to enable compiling against system PHP.

✩✩✩✩ PHP CLI ✩✩✩✩

If you wish to swap the PHP you use on the command line, you should add the following to ~/.bashrc, ~/.zshrc, ~/.profile or your shell's equivalent configuration file:
  export PATH="$(brew --prefix homebrew/php/php56)/bin:$PATH"
 


✩✩✩✩ FPM ✩✩✩✩

To launch php-fpm on startup:
    mkdir -p ~/Library/LaunchAgents
    cp /usr/local/opt/php56/homebrew.mxcl.php56.plist ~/Library/LaunchAgents/
    launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.php56.plist

The control script is located at /usr/local/opt/php56/sbin/php56-fpm

OS X 10.8 and newer come with
 
 php-fpm pre-installed, to ensure you are using the brew version you need to make sure /usr/local/sbin is before /usr/sbin in your PATH:

  PATH="/usr/local/sbin:$PATH"

You may also need to edit the plist to use the correct "UserName".

Please note that the plist was called 'homebrew-php.josegonzalez.php56.plist' in old versions of this formula.

With the release of macOS Sierra the Apache module is now not built by default. If you want to build it on your system you have to install php with the --with-httpd24 option. See  brew options php56 for more details.

To have launchd start homebrew/php/php56 now and restart at login:
  brew services start homebrew/php/php56
==> Summary

我是用的命令列工具是 zsh
在 ~/.zshrc 檔案的最後一行加上

export PATH="$(brew --prefix homebrew/php/php56)/bin:$PATH"

然後source .zshrc，並檢視 PHP 版本 php -v，發現以下錯誤：

dyld: Library not loaded: /usr/local/opt/jpeg/lib/libjpeg.8.dylib
  Referenced from: /usr/local/opt/php56/bin/php
  Reason: image not found
[1]    19810 trace trap  php -version

後來在 stackoverflow 看到一些解決辦法，一個一個試試：

對我有效的辦法是

brew uninstall php56
brew install --build-from-source php56