php insert text into a href

I'm working on using htmlpurifier to create a text-only version of my site. I now need to replace all the a hrefs with the text only url i.e. 'www.example.com/aboutus' becomes 'www.example.com/text/aboutus'

Initially I tried a simple str_replace on the domain (I use a global variable for the domain), but the problem is links to files also get replaced i.e. 'www.example.com/document.pdf' becomes 'www.example.com/text/document.pdf' and therefore fails.

Is there a regular expression where I can say replace domain w开发者_如何转开发ith domain/text where the url does not include string?

Thanks for any pointers you might be able to give me :)

---

Use a negative lookahead:

$output = preg_replace(
             '#www.example.com(?!/text/)#', 
             'www.example.com/text', 
             $input
          );

Better yet, use DOM with it:

$html = '<a href="www.example.com/something">foo</a>
         <p>hello</p>
         <a href="www.example.com/text/documents">bar</a>';

libxml_use_internal_errors(true); // supresses DOM errors

$dom = new DOMDocument;
$dom->loadHTML($html);
$xpath = new DOMXPath($dom);

$hrefs = $xpath->query('//a/@href');
foreach ($hrefs as $href) {
    $href->value = preg_replace(
                      '#^www.example.com(?!/text/)(.*?)(?<!\.pdf)$#', 
                      'www.example.com/text\\1', 
                      $href->value
                   );
}

This should give you:

<a href="www.example.com/text/something">foo</a>
<p>hello</p>
<a href="www.example.com/text/documents">bar</a>