Install or enable PHP‘s pcntl extension._install or enable php's pcntl extension

问题原因：

laravel项目执行 composer install时报错，报错信息如下：

Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Your lock file does not contain a compatible set of packages. Please run composer update.
 
  Problem 1
    - hhxsv5/laravel-s is locked to version v3.7.0 and an update of this package was not requested.
    - hhxsv5/laravel-s v3.7.0 requires ext-pcntl * -> it is missing from your system. Install or enable PHP's pcntl extension.
To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php.ini
You can also run `php --ini` in a terminal to see which files are used by PHP in CLI mode.
Alternatively, you can run Composer with `--ignore-platform-req=ext-pcntl` to temporarily ignore these required extensions.

google 结果：Process Control support in PHP is not enabled by default. You have to compile the CGI or CLI version of PHP with --enable-pcntl configuration option when compiling PHP to enable Process Control support.

大意就是这个配置默认是不被开启的，需要在编译php的时候使用 --enable-pcntl 参数开启

从https://www.php.net/releases/网站下载7.3.22版本源码在本地mac上编译，结果编译过程报错；后续原因没有继续追查，感觉以目前认知解决比较困难；

因此整理了一下比较不需要底层信息的解决方式：

仅针对mac 且 php version = 7.3

具体操作如下：

1.使用brew search php 查找brew 支持的php版本

2.执行brew install php@7.3

        如果执行报错：那么google php 第三方brew资源库

        执行brew tap shivammathur/php

        重新brew search

        注：shivammathur/php 是我当时搜到的可用的资源

3.将brew install 之后的php@7.3添加到环境变量中

        export PATH="/usr/local/opt/php@7.3/bin:$PATH"

        export PATH="/usr/local/opt/php@7.3/sbin:$PATH"

        export LDFLAGS="-L/usr/local/opt/php@7.3/lib"

        export CPPFLAGS="-I/usr/local/opt/php@7.3/include"

4.使用php -v验证添加之后的php版本信息

5.再次执行composer install显示成功

其中遇到的问题：使用这个第三方库安装php@7.0 直接执行php命令报错；安装php@7.3可用