PHP Regular Expressions: How to match all lists in HTML

In web development, it is very common to display content in lists. When processing and parsing HTML files, regular expressions can be used to more easily match the corresponding content. This article will introduce how to match all lists in HTML using PHP regular expressions.

1. Web page text acquisition
   Before processing the HTML list, you need to obtain the text content of the HTML file first. You can use PHP's file_get_contents function to get the entire text content of the HTML file. The code is as follows:

$html = file_get_contents('example.html');

2. Match unordered list
   The first is the unordered list. Unordered lists are implemented through ul tags and li tags. The ul tag is used to represent the entire list, and the li tag represents each item in the list. We can use the regular expression <ul>(.*?)</ul> to match all unordered lists. Among them, ? indicates that this match is non-greedy, and the matched content will be selected as small as possible, so that multiple lists will not be connected together for batch matching. The complete code is as follows:

preg_match_all('/<ul>(.*?)</ul>/s', $html, $matches);

foreach ($matches[0] as $key => $value) {
    echo $key . ': ' . $value . '<br>';
}

In the above code, the preg_match_all function can perform multiple matches and save the matching results to $matches. And /s means . matches all characters including newlines. Finally, use foreach to traverse and output the matching results.

3. Match ordered list
   Ordered list is implemented through ol and li tags. The ol tag is used to represent an ordered list, while li represents each item in it. Regular expressions are basically the same as the above unordered list matching methods. The regular expression for matching ordered lists is:

preg_match_all('/<ol>(.*?)</ol>/s', $html, $matches);

foreach ($matches[0] as $key => $value) {
    echo $key . ': ' . $value . '<br>';
}

Similarly, you can use the preg_match_all function to match and use foreach to output the results. .

4. Match custom lists
   Custom lists are implemented through dl, dt and dd tags. The dl tag is used to represent the definition list, the dt tag is used to represent the name of the custom item, and the dd tag is used to represent the description of the custom item. The regular expression is as follows:

preg_match_all('/<dl>(.*?)</dl>/s', $html, $matches);

foreach ($matches[0] as $key => $value) {
    echo $key . ': ' . $value . '<br>';
}

Similarly, use the preg_match_all function to match, and use foreach to output the results.

5. Match all lists
   Although the matching methods of the above three lists are different, the regular expressions are very similar. If you need to match all lists in HTML, you can use a simple regular expression.

The regular expression that matches all lists is: /(.*?)[ou]l>/s.

Among them, [ou] represents the character set, which means matching o or u. Use the preg_match_all function for matching, the code is as follows:

preg_match_all('/<[ou]l>(.*?)</[ou]l>/s', $html, $matches);

foreach ($matches[0] as $key => $value) {
    echo $key . ': ' . $value . '<br>';
}

The above code will match all lists in HTML and output the matching results.

Summary
When processing HTML files, using regular expressions can match the corresponding content more conveniently and quickly. When matching HTML lists, you can match based on the tags of different types of lists. At the same time, you can also combine the matching methods of the three list types and use one regular expression to match all lists, which is more convenient.

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