我们常常会用到PHP过滤一些标签的功能，比如过滤链接标签、过滤script标签等等，下面就介绍一下PHP过滤常用标签的正则表达式代码：

$str=preg_replace("/s+/", " ", $str); //过滤多余回车 $str=preg_replace("/<[ ]+/si","<",$str); //过滤<__("<"号后面带空格) $str=preg_replace("/<!–.*",$str); //注释 $str=preg_replace("/<(!.*",$str); //过滤DOCTYPE $str=preg_replace("/<(/?html.*",$str); //过滤html标签 $str=preg_replace("/<(/?head.*",$str); //过滤head标签 $str=preg_replace("/<(/?meta.*",$str); //过滤meta标签 $str=preg_replace("/<(/?body.*",$str); //过滤body标签 $str=preg_replace("/<(/?link.*",$str); //过滤link标签 $str=preg_replace("/<(/?form.*",$str); //过滤form标签 $str=preg_replace("/cookie/si","COOKIE",$str); //过滤COOKIE标签 $str=preg_replace("/<(applet.*?)>(.*?)<(/applet.*",$str); //过滤applet标签 $str=preg_replace("/<(/?applet.*",$str); //过滤applet标签 $str=preg_replace("/<(style.*?)>(.*?)<(/style.*",$str); //过滤style标签 $str=preg_replace("/<(/?style.*",$str); //过滤style标签 $str=preg_replace("/<(title.*?)>(.*?)<(/title.*",$str); //过滤title标签 $str=preg_replace("/<(/?title.*",$str); //过滤title标签 $str=preg_replace("/<(object.*?)>(.*?)<(/object.*",$str); //过滤object标签 $str=preg_replace("/<(/?objec.*",$str); //过滤object标签 $str=preg_replace("/<(noframes.*?)>(.*?)<(/noframes.*",$str); //过滤noframes标签 $str=preg_replace("/<(/?noframes.*",$str); //过滤noframes标签 $str=preg_replace("/<(i?frame.*?)>(.*?)<(/i?frame.*",$str); //过滤frame标签 $str=preg_replace("/<(/?i?frame.*",$str); //过滤frame标签 $str=preg_replace("/<(script.*?)>(.*?)<(/script.*",$str); //过滤script标签 $str=preg_replace("/<(/?script.*",$str); //过滤script标签 $str=preg_replace("/javascript/si","Javascript",$str); //过滤script标签 $str=preg_replace("/vbscript/si","Vbscript",$str); //过滤script标签 $str=preg_replace("/on([a-z]+)s*=/si","On1=",$str); //过滤script标签 $str=preg_replace("/",$str); //过滤script标签