How to remove html tags with regular expressions

HTML tags are very important when developing web applications. Especially in the field of front-end development, HTML tags are often used to build website layout, style, and the appearance of applications.

However, sometimes we need to extract or process data from these tags instead of displaying the page content. In this case, a way is needed to strip HTML tags and extract plain text. This process is often called "regular HTML tag removal".

In this article, we will introduce how to use regular expressions to remove HTML tags and extract plain text.

Regular expressions are a general text processing tool that can be used to find and replace specific patterns in text. In PHP, JavaScript, and other programming languages, we can use regular expressions to represent patterns to search for and then use them to process text.

In this article, we will use PHP’s preg_replace function to replace HTML tags. This function accepts three parameters: the pattern to replace, the text to replace with, and the source text to scan.

Here is a sample PHP code to get text from HTML tags without using regular expressions:

$html_text = '<p>这是一个段落。</p><div><h1>这是一个标题</h1></div>';

$text = strip_tags($html_text);

echo $text;

In this example, we pass the string containing the HTML tags Give PHP's strip_tags function to strip all HTML tags. This function is a built-in function of PHP and is very easy to use.

Another way is to use regular expressions. Here is a PHP code example using the preg_replace function to remove HTML tags:

$html_text = '<p>这是一个段落。</p><div><h1>这是一个标题</h1></div>';

$pattern = '/<[^>]*>/';

$text = preg_replace($pattern, '', $html_text);

echo $text;

In this example, we use the regular expression pattern "/<¹* >/" to match HTML tags. This pattern tells the regular expression engine to match any string that starts with "<" and ends with ">" and contains zero or more non-">" characters. This pattern will match any HTML tag.

Now that we have completed the basics of regular expressions, here are some more complex examples.

Delete a specific tag

To delete a specific HTML tag, we can include the name of this tag in the regular expression. For example, to remove all P tags, we can use the following code:

$pattern = '/<p[^>]*>/';

$text = preg_replace($pattern, '', $html_text);

In this example, we include the name of the "P" tag in the pattern and use an asterisk symbol to indicate that the Any characters after

In the above code, if we also want to remove the "/p" tag, we can use the following code:

$pattern = &#39;/<[/]?p[^>]*>/';

$text = preg_replace($pattern, '', $html_text);</p>
<p>In this example, we have added an optional The closing tag of the selection ("</p>") and a question mark symbol are used to indicate that it is optional. This pattern will match the opening and closing P tags. </p>
<p>Extract Link</p>
<p>Sometimes, we need to extract specific data from HTML tags. For example, we might need to extract the URL from a link tag. To extract a link we can use the following code: </p>
<pre class="brush:php;toolbar:false">$html_text = '<a href="http://www.example.com">这是一个链接</a>';

$pattern = '/<a\s+href="([^"]+)">([^<]+)<\/a>/i';

preg_match($pattern, $html_text, $matches);

$url = $matches[1];

echo $url;

In this example we use a more specific pattern that matches an "A" tag and use a sub-pattern to extract URL and link text.

In the regular expression, we use the "/i" modifier to make the match case-insensitive. This modifier is very useful when we search for attributes and attribute values ​​of tags.

Summary

In this article, we introduced regular expressions and their application in removing HTML tags. We explored some common regex patterns, including removing all tags, removing specific tags, and extracting links.

To become a good web developer, we need to have a deep understanding of HTML tags and regular expressions. Using regular expressions to remove HTML tags can greatly improve our efficiency and the performance of web applications.

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