Отличный карринг на PHP!

function phpbb_links_abstract_helper($matches, $letter)
{
    $url = substr($matches[0], strlen('[url]'));
    $url = substr($url, 0, -strlen('['));

    return '[url=' . $url . ']' . $letter . '=' . $matches[1] . '[';
}

function create_phpbb_links_helper($letter)
{
    return create_function('$matches', 'return phpbb_links_abstract_helper($matches, ' . var_export($letter, true) . ');');
}

$text = preg_replace_callback('#\[url\]' . preg_quote($vbulletin->options['bburl']) . '.*showthread\.php\?.*t=([0-9]+[^\[]*)\[#i', create_phpbb_links_helper('t'), $text);
$text = preg_replace_callback('#\[url\]' . preg_quote($vbulletin->options['bburl']) . '.*showthread\.php\?.*p=([0-9]+[^\[]*)\[#i', create_phpbb_links_helper('p'), $text);
$text = preg_replace_callback('#\[url\]' . preg_quote($vbulletin->options['bburl']) . '.*forumdisplay\.php\?.*f=([0-9]+[^\[]*)\[#i', create_phpbb_links_helper('f'), $text);