PHP preg_replace与自定义网址的怪异

Question

I'm using the following code to add <span> tags behind <a> tags.

$html = preg_replace("~<a.*?href=\"$url\".*?>.*?</a>~i", "$0<span>test</span>", $html);

The code is working fine for regular links (ie. http://www.google.com/), but it will not perform a replace when the contents of $url are $link$/3/.

This is example code to show the (mis)behaviour:

<?php
    $urls = array();
    $urls[] = '$link$/3/';
    $urls[] = 'http://www.google.com/';

    $html = '<a href="$link/3/">Test Link</a>' . "
" . '<a href="http://www.google.com/">Google</a>';

    foreach($urls as $url) {
        $html = preg_replace("~<a.*?href=\"$url\".*?>.*?</a>~i", "$0<span>test</span>", $html);
    }

    echo $html;
?>

And this is the output it produces:

<a href="$link$/3/">Test Link</a>
<a href="http://www.google.com/">Google</a><span>test</span>

Answer 1

$url = preg_quote($url, '~'); the dollar signs are interpreted as usual: end-of-input.