How to test the contents of the special value perch_page_path?

I can use this special value in a template to show the path to the current page ... <perch:content id="perch_page_path" type="hidden" />. As expected this shows the text of (for example) /xxx/yyy/index.php on the page. However, I don't want to display the value, but want to test against its value/contents.

Is there a way I can test another field in the template against the content of that special value (and removing the '/index.php' part)?

Basically, I have a multiple item field and want to do something different in the template on one of the multiple-items, and only if the value in the field equals /xxx/yyy (in other words the contents of id="perch_page_path" with the /index.php stripped off it).

I have tried this ...

<perch:if id="link" value="{perch_page_path}" match="contains">

But it gives this error in page debug ...

Array
(
    [type] => 2
    [message] => preg_match(): Unknown modifier 'p'
    [file] => /home/xxxxxx/public_html/dev/perch/core/lib/PerchTemplate.class.php
    [line] => 1115
)

Graham