Regular expression matching html and filtering illegal characters_PHP tutorial

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Regular expression matching html to filter illegal characters
To match an html tag, the matching table is as follows:

[ss]*[ss]*
或
[ss]*?*?>*?>

以上两个表达式，一个加了"?"和一个却不加"?"，那么这有什么区别呢？
我们知道"?"在正则表达式里是一个通配符：匹配前面的子表达式零次或一次，或指明一个非贪婪限定符。

在这里，通过测试，我们得出这样的结论：在不加"?"的情况下，在匹配下面一段内容的时候：

 

这是第一个table or
[ss]*?*?>*?>
The above two expressions, one adds "?" and the other does not add "?", so what is the difference?
We know that "?" is a wildcard character in regular expressions: it matches the previous subexpression zero or once, or specifies a non-greedy qualifier.
Here, through testing, we come to this conclusion: without adding "?", when matching the following content:

This is the first table

I am not the content in the table

This is the second table

I am not the content in the table either

This is the third table





$str=preg_replace("/s+/", " ", $str); //Filter redundant carriage returns
$str=preg_replace("/

$str=preg_replace("/

/si","",$str); //Comments
$str=preg_replace("//si","",$str); //Filter doctype

$str=preg_replace("//si","",$str); //Filter html tags

$str=preg_replace("//si","",$str); //Filter head tag
$str=preg_replace("//si","",$str); //Filter meta tags

$str=preg_replace("//si","",$str); //Filter body tag

$str=preg_replace("//si","",$str); //Filter link tag
$str=preg_replace("//si","",$str); //Filter form tag

$str=preg_replace("/cookie/si","cookie",$str); //Filter cookie tags

$str=preg_replace("/(.*?)/si","",$str); //Filter applet tag

$str=preg_replace("//si","",$str); //Filter applet tags

$str=preg_replace("/(.*?)/si","",$str); //Filter style tag

$str=preg_replace("//si","",$str); //Filter style tag

$str=preg_replace("/(.*?)/si","",$str); //Filter title tag

$str=preg_replace("//si","",$str); //Filter title tag

$str=preg_replace("/(.*?)/si","",$str); //Filter object tag
$str=preg_replace("//si","",$str); //Filter object tag

$str=preg_replace("/(.*?)/si","",$str); //Filter noframes tag
$str=preg_replace("//si","",$str); //Filter noframes tag

$str=preg_replace("/(.*?)/si","",$str) ; //Filter frame tag

$str=preg_replace("//si","",$str); //Filter frame tag
$str=preg_replace("/(.*?)/si","",$str); //Filter script tag

$str=preg_replace("//si","",$str); //Filter script tags

$str=preg_replace("/Webpage Special Effects/si","javascript",$str); //Filter script tags $str=preg_replace("/vbscript/si","vbscript",$str); //Filter script tags $str=preg_replace("/on([a-z]+)s*=/si","on1=",$str); //Filter script tags $str=preg_replace("//si","",$str); //Filter script tags, such as javascript: alert('aabb) ?> http://www.bkjia.com/PHPjc/445418.html

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http: //www.bkjia.com/PHPjc/445418.htmlTechArticleRegular expression matching html filters illegal characters to match an html tag. The matching table is as follows: [ss]* or [ss ]*? The above two expressions, one with ? and one without ?, so what does this mean...