Replace the content of a tag with a certain class

Question

I am looking for suitable replacement code that allows me replace the content inside of any HTML tag that has a certain class e.g.

$class = "blah";
$content = "new content";
$html = '<div class="blah">hello world</div>';

// code to replace, $html now looks like:
// <div class="blah">new content</div>

Bare in mind that:

1. It wont necessarily be a div, it could be <h2 class="blah">
2. The class can have more than one class and still needs to be replaced e.g. <div class="foo blah green">hello world</div>

I am thinking regular expressions should be able to do this, if not I am open to other suggestions such as using the DOM class (although I would rather avoid this if possible because it has to be PHP4 compatible).

Answer 1

Do not use regular expressions to parse HTML. You can use the built in DOMDocument, or something like simple_html_dom:

require_once("simple_html_dom.php");

$class = "blah";
$content = "new content";
$html = '<div class="blah">hello world</div>';

$doc = new simple_html_dom();
$doc->load($html);

foreach ( $doc->find("." . $class) as $node ) {
    $node->innertext = $content;
}

Sorry, I didn't see the PHP4 requirement. Here's a solution using the standard DOMDocument as mentioned above.

function DOM_getElementByClassName($referenceNode, $className, $index=false) {
    $className = strtolower($className);
    $response  = array();

    foreach ( $referenceNode->getElementsByTagName("*") as $node ) {
        $nodeClass = strtolower($node->getAttribute("class"));

        if (
                $nodeClass == $className || 
                preg_match("/\b" . $className . "\b/", $nodeClass)
            ) {
            $response[] = $node;
        }
    }

    if ( $index !== false ) {
        return isset($response[$index]) ? $response[$index] : false;
    }

    return $response;
}

$doc = new DOMDocument();
$doc->loadHTML($html);

foreach ( DOM_getElementByClassName($doc, $class) as $node ) {
    $node->nodeValue = $content;
}

echo $doc->saveHTML();

Answer 2

If you are sure that $html is valid HTML code, you could use a HTML parser or even XML parser if it's valid XML code.

But the quick and dirty way in Regex would be something like:

$html = preg_replace('/(<[^>]+ class="[^>]*' . $class . '[^"]*"[^>]*>)[^<]+(<\/[^>]+>)/siU', '$1' . $content . '$2', $html);

Didn't test it too much, but it should work. Tell me if you find cases where it doesn't. ;)

Edit: Added "and dirty"... ;)

Edit 2: New version of the RegEx:

<?php

$class = "blah";
$content = "new content";
$html = '<div class="blah test"><h1><span>hello</span> world</h1></div><div class="other">other content</div><h2 class="blah">remove this</h2>';

$html = preg_replace('/<([\w]+)(\s[^>]*class="[^"]*' . $class . '[^"]*"[^>]*>).+(<\/\\1>)/siU', '<$1$2' . $content . '$3', $html);

echo $html;

?>

The last problem left is if theres a class that only has "blah" in its name, like "tooMuchBlahNow". Let's see how we can address that. Btw: Is it obvious already that I love playing with RegEx? ;)

Answer 3

There is no need to use the DOM class, this would probably be done quickest using jQuery, as Khnle said, or you could use the preg_replace() function. Give me some time, I may write a quick regex for you.

But I would recommend using something like jQuery, this way you can serve the page up to the user quickly and allow their computer to do the processing instead of your server.