PHP Regular Expressions: How to match all stylesheets in HTML

In front-end development, processing style sheets in HTML is one of the common tasks. Use PHP regular expressions to easily match all style sheets in HTML and perform related operations on them.

1. HTML style sheet

First of all, before understanding how to match the style sheet in HTML, you need to understand what an HTML style sheet is. HTML style sheet is a technology that defines document styles. You can specify font color, size, background color and other styles in HTML documents to ultimately present the website that users see.

A simple style sheet is as follows:

<style>
    body {
        background-color: lightblue;
        font-family: Arial, Helvetica, sans-serif;
    }
    h1 {
        color: maroon;
        margin-left: 40px;
    }
</style>

In actual scenarios, HTML style sheets are often more complex, containing multiple style definition blocks, nested layer by layer, and involving inheritance. and priority issues. How to process these style sheets quickly is a challenge.

2. PHP regular expression

PHP regular expression is a powerful tool for string matching and is often used to parse and process various text data. In PHP, you can use functions such as preg_match to match regular expressions to achieve fast search and processing of text.

Below, we will use PHP regular expressions to match all style sheets in HTML.

3. Match all style sheets in HTML

In HTML, each style sheet is contained in the <style> tag, so it can be matched<style> tag to locate each style sheet. First, we need to read the content of the HTML file:

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

After reading the HTML file, use the preg_match_all function to match all the <style> tags in it. The code is as follows:

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

Among them, the meaning of the regular expression is as follows:

• <style.*>: Matches those starting with <style> Tag, where .* means matching any number of characters;
• .*</style>: matches the middle style sheet content, where .* means matching any number of characters, < ;/style> Matches the </style> tag at the end;
• /s: indicates using single-line mode, that is, matching text that spans multiple lines.

After successful matching, the contents of all style sheets are stored in the $matches variable. You can use a foreach loop to traverse each content and process it, such as outputting it to a file:

$file = fopen('styles.css', 'w');
foreach ($matches[0] as $match) {
    fwrite($file, $match);
    fwrite($file, "
");
}
fclose($file);

After completing the above operations, you can find all the style sheets in the HTML file in the styles.css file.

4. Summary

Using PHP regular expressions can easily match all style sheets in HTML to further process and parse HTML files. Regular expressions are a powerful tool, but they also need to be used with caution, especially for complex text processing tasks that require comprehensive processing in combination with other tools and techniques.

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