How to match HTML tag attribute value using regular expression in PHP-PHP Tutorial-php.cn

How to match HTML tag attribute value using regular expression in PHP

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Release： 2023-06-24 12:38:01

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With the development of the Internet, HTML, as the standard language for web pages, plays a very important role in Web development. In web page production, it is often necessary to match and modify the attributes of HTML tags. Regular expressions are one of the tools that can solve this problem. In this article, we will explain how to match HTML tag attribute values using regular expressions in PHP.

1. Basic syntax of regular expressions

In regular expressions, each character can represent a syntax. Here are some basic characters and their meanings:

^: Starting position of the line
$: Ending position of the line
.: Matches except newline characters Any character except
*: matches the previous character 0 to multiple times
: matches the previous character 1 to multiple times
?: matches the previous character 0 or 1 times
[]: character set, matching any character within the brackets
|: OR operator, matching any character on both sides of |
(): grouping symbol , match the content in the brackets as a whole

2. Use regular expressions to match HTML tag attribute values in PHP

Let’s use an example to demonstrate how to match the HTML tag attribute value in PHP Use regular expressions to match attribute values of HTML tags.

Suppose we have the following HTML code:


    
        
            这是第一段文字
            这是第二段文字
            这是第三段文字

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We need to find all

tags and get their id attribute values.

The following is the PHP code implementation:


                
                    
                        这是第一段文字
                        这是第二段文字
                        这是第三段文字
                    
                
            ';
 
    // 定义正则表达式
    $pattern='/]*s+id=["']([^"']+)["'][^>]*>/i';
 
    // 执行匹配
    if(preg_match_all($pattern, $html, $match)){
        // 输出匹配结果
        var_dump($match[1]);
    }
?>

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In the above code, we first define the HTML code that needs to be matched, then define a regular expression, perform the matching operation through the preg_match_all function, and finally Output matching results.

3. Analysis of regular expressions

If you have some doubts about the above regular expressions, we will analyze them one by one below.

tag matching

The first part of the regular expression is , which is used to match the

tag the beginning of. This part is very simple, it directly matches the first letter < of the

tag and the following characters p.


Matching of attribute values
The second part of the regular expression is [^>]*s , which is mainly used to match < p>Attributes part of the tag. 
[^>]* means matching any character except >`, and allows 0 to multiple matches, which means that spaces and other characters before the attribute can be Matched. 
The following s  means matching any space character, and allows 1 to multiple matches. 
The purpose of this step is to match any attribute of the 
 tag, and can handle space symbols between multiple attributes. 
Matching of id attribute values
The third part of the regular expression isid=["']([^"'] )["' ], used to match the value of the id attribute. 
Where id= indicates that the attribute name to be matched is id. 
["']  means that it can match single quotes ' or double quotes ". 
([^"'] )  means that it matches except single quotes ' or any character except double quotation marks ", and one or more matches are allowed. 
The brackets used here are () , used to group matching results for subsequent use. Matching of 
 symbols 
 The last part of the regular expression is  [^>]*> means matching the trailing symbol > of the 
 tag. 
Among them, [^>]*Same as the previous function, used to match any character before >. 
The final function of this regular expression is to match all 
 tags and extract their id attribute values.
4. Summary
Regular expression is a powerful tool for processing strings. It can be used to quickly complete operations such as string matching, replacement, and extraction. In actual Web development At work, we often need to use regular expressions to handle attribute value matching of HTML tags. In PHP, the preg_match_all function can implement this function very conveniently. We only need to define the regular expression and then call the function to perform matching. .Through the introduction of this article, I believe everyone can better understand and master the method of using regular expressions to match HTML tag attribute values in PHP.
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