尝试了brew tap 修改源，但是会报错，去了提示的githup里寻找，有人提了issue，但是没有被解决。所以尝试用brew install php56 的话，基本上没戏。尝试失败

所以采用源码安装
环境：mac pro,系统 10.13.6

1、下载源码
到目录 /usr/local/src 下执行命令，

sudo wget -c http://cn2.php.net/distributions/php-5.6.40.tar.gz

此时提示没用wget, brew install wget安装即可
解压压缩文件

tar -xzvf php-5.6.40.tar.gz

2、执行 configure命令

sudo ./configure \
--prefix=/usr/local/php5.6 \
--with-mysql \
--with-gd \
--enable-gd-native-ttf \
--enable-gd-jis-conv \
--with-freetype-dir=/usr/local/Cellar/freetype/2.9.1 \
--with-jpeg-dir=/usr/local/Cellar/libjpeg \
--with-png-dir=/usr/local/Cellar/libpng \
--with-libxml-dir=/usr/local/Cellar/libxml2 \
--with-zlib-dir=/usr/local/Cellar/zlib/1.2.11 \
--with-iconv=/usr/local/Cellar/libiconv/1.15 \
--enable-xml \
--enable-mbstring \
--enable-sockets \
--enable-simplexml \
--enable-soap \
--enable-mbstring=all \
--enable-sockets \
--enable-bcmath \
--enable-pdo \
--with-curl=/usr/local/Cellar/curl \
--with-config-file-path=/usr/local/php5.6/etc \
--with-mhash \
--enable-cli \
--enable-fpm \
--with-pdo-mysql

3、执行 make

sudo make && sudo make install

4、运行 php-fpm,一般安装成功后会提示命令

sudo /usr/local/php5.6/sbin/php-fpm
[29-Sep-2019 07:44:41] ERROR: failed to open configuration file '/usr/local/php5.6/etc/php-fpm.conf': No such file or directory (2)
[29-Sep-2019 07:44:41] ERROR: failed to load configuration file '/usr/local/php5.6/etc/php-fpm.conf'
[29-Sep-2019 07:44:41] ERROR: FPM initialization failed

这里会报错，这里需要弄一下默认配置文件,进入到配置目录
cd /usr/local/php5.6/etc/

sudo cp php-fpm.conf.default php-fpm.conf

再次执行，成功

复制配置文件
sudo cp php.ini-development /usr/local/lib/php.ini