How can I exclude regex href matches of a particular domain? - php

Question

How can I exclude href matches for a domain (ex. one.com)?
My current code:
$str = 'This string has one link and another link';
$str = preg_replace('~<a href="(https?://[^"]+)".*?>.*?</a>~', '$1', $str);
echo $str; // This string has http://one.com and http://two.com
Desired result:
This string has one link and http://two.com

Answer 1

Using a regular expression
If you're going to use a regular expression to accomplish this task, you can use a negative lookahead. It basically asserts that the part // in the href attribute is not followed by one.com. It's important to note that a lookaround assertion doesn't consume any characters.
Here's how the regular expression would look like:
<a href="(https?://(?!one\.com)[^"]+)".*?>.*?</a>
Regex Visualization:
Regex101 demo
Using a DOM parser
Even though this is a pretty simple task, the correct way to achieve this would be using a DOM parser. That way, you wouldn't have to change the regex if the format of your markup changes in future. The regex solution will break if the <a> node contains more attribute values. To fix all those issues, you can use a DOM parser such as PHP's DOMDocument to handle the parsing:
Here's how the solution would look like:
$dom = new DOMDocument();
$dom->loadHTML($html); // $html is the string containing markup
$links = $dom->getElementsByTagName('a');
//Loop through links and replace them with their anchor text
for ($i = $links->length - 1; $i >= 0; $i--) {
$node = $links->item($i);
$text = $node->textContent;
$href = $node->getAttribute('href');
if ($href !== 'http://one.com') {
$newTextNode = $dom->createTextNode($text);
$node->parentNode->replaceChild($newTextNode, $node);
}
}
echo $dom->saveHTML();
Live Demo

Answer 2

This should do it:
<a href="(https?://(?!one\.com)[^"]+)".*?>.*?</a>
We use a negative lookahead to make sure that one.com does not appear directly after the https?://.
If you also want to check for some subdomains of one.com, use this example:
<a href="(https?://(?!((www|example)\.)?one\.com)[^"]+)".*?>.*?</a>
Here we optionally check for www. or example. before one.com. This will allow a URL like misc.com, though. If you want to remove all subdomains of one.com, use this:
<a href="(https?://(?!([^.]+\.)?one\.com)[^"]+)".*?>.*?</a>