Question

I receive a text formatted as html. I want to restrict anchor tag’s urls to be only from my domain replacing the old links with “xxx” (or smth’ else).
Input: “<a href='otherdomain'>text</a>“
Output: “xxx”
I am using regexp to achieve this though I’m kind of stuck here:

$pattern ='/<a.*href=[\'|\"]http.?:\/\/[^mydomain.*\"\']*[\'|\"].*<\/a>/i';
$replace ='xxx';
echo preg_replace($pattern, $replace, $string); 

What is wrong here?

Answer 1

When you do [^mydomain.*\"\'] you are saying “match any character except a literal ‘m’, ‘y’, ‘d’, ‘o’, …, ‘.’, ‘*’, etc.

Try something like:

#<a [^>]*\bhref=(['"])http.?://((?!mydomain)[^'"])+\1 *>.*?</a>#i

Notes:

• I turned your a.*href to a [^>]*\bhref to make sure that the ‘a’ and ‘href’ are whole words and that the regex doesn’t match over multiple tags.
• I changed the regex delimiter character to ‘#’ instead of ‘/’ so you don’t have to escape the / any more
• Note the ((?!mydomain)[^'"])+. This means “match [^'”]+ that isn’t mydomain”. The (?! is called a negative look-ahead.
• Note the \1. This makes sure that the closing quote mark for the URL is the same as the opening quote mark (see hwo the first set of brackets captures the ['"]?). You’d probably be fine without it if you prefered.

For PHP (updated because I always mix up when backslashes need to be escaped in PHP — see @GlitchMr’s comment below):

$pattern = '#<a [^>]*\bhref=([\'"])http.?://((?!mydomain)[^\'"])+\1 *>.*?</a>#i';

See it in action here, where you can tweak it to your purposes.