PHP regular expression: how to match all img tags in HTML

Regular expression is a powerful string processing tool that can find, replace and match specific patterns in text. Regular expressions are widely used in PHP development, especially when dealing with HTML and other text formats. This article will show you how to use regular expressions to match all img tags in HTML.

First, we need to understand the basic structure of the img tag. A simple img tag usually contains the following attributes:

• src: specifies the URL of the image.
• alt: Alternative text for the image, which will be displayed when the image cannot be displayed.
• width and height: The width and height of the image, in pixels.

The sample code is as follows:

<img src="example.jpg" alt="Example Image" width="200" height="150">

Now, we can use regular expressions to match all img tags in HTML. Here is a simple regular pattern that matches all legal img tags:

/<s*imgs+[^>]*>/i

Let’s parse this regular expression one by one.

• /: The boundary of the regular expression, indicating the start of matching.
• <: Matches the left angle bracket.
• s*: Matches any number of spaces.
• img: Matches the string "img".
• s : Matches at least one space.
• ¹*: Matches any character except the right angle bracket, repeated zero or more times.

• : Matches the right angle bracket.

• /i: Regular expression flag, indicating that it is not case-sensitive.

Now, we can use PHP’s preg_match_all() function to apply regular expressions. This function can perform global regular matching in a string and return all matching results. Here is a sample code:

$html = '
         ';

$pattern = '/<s*imgs+[^>]*>/i';
preg_match_all($pattern, $html, $matches);

print_r($matches[0]);

In the above code, we first define a string variable $html, which contains two img tags. Then, we define a regular expression pattern $pattern to match all img tags. Finally, we use the preg_match_all() function to apply the regular expression and store the result in the variable $matches. Finally, we output the first element in the variable $matches, which is an array of all matching results.

The output of the above code is as follows:

Array
(
    [0] => <img src="example1.jpg" alt="Example Image 1" width="200" height="150">
    [1] => <img src="example2.jpg" alt="Example Image 2" width="200" height="150">
)

As shown above, we successfully matched all img tags in the HTML and saved them in the $matches array. In practical applications, we can further process these matching results, such as extracting the URL, width, height and other attributes of each img tag.

In short, regular expressions are a very useful tool that can be used to process various text formats. In PHP development, regular expressions are often used to parse data in HTML, XML, and other formats. This article explains how to use regular expressions to match all img tags in HTML, and how to use PHP's preg_match_all() function for global regular matching. Hope this article will be helpful to PHP developers.

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