在CentOS / Red Hat下安装PHP 5.x PECL Filter Extension
php 5.2之后，默认会装有filter extension，这个扩展可以帮助php开发者过滤用户输入的内容，由php的创始人之一Rasmus Lerdorf提供，可以见我早期的文章介绍。
Q. How do I install filter extension for safely dealing with input parameters supplied via a web form using filter_var()?
A. This extension is part of PHP Core version 5.20 and above. Unfortunately, RHEL / CentOS comes with PHP version 5.1.6. So you need to install this extension by typing the following commands.