Change language directory in a URL string

I use Codeigniter to create a multilingual website and everything works fine, but when I try to use the "alternative languages helper" by Luis I've got a problem. This helper uses a regular expression to replace the current language with the new one:

$new_uri = preg_replace('/^'.$actual_lang.'/', $lang, $uri);

The problem is that I have a URL like this: http://www.example.com/en/language/english/ and I want to replace only the first "en" without changing the word "english". I tried to use the limit for preg_replace:

$new_uri = preg_replace('/^'.$actual_lang.'/', $lang, $uri, 1);

but this doesn't work for me. Any ideas?

You could do something like this:

$regex = '#^'.preg_quote($actual_lang, '#').'(?=/|$)#';
$new_uri = preg_replace($regex, $lang, $uri);

The last capture pattern basically means "only match if the next character is a forward slash or the end of the string"...

Edit:

If the code you always want to replace is at the beginning of the path, you could always do:

if (stripos($url, $actual_lang) !== false) {
    if (strpos($url, '://') !== false) {
        $path = parse_url($url, PHP_URL_PATH);
    } else {
        $path = $url;
    }
    list($language, $rest) = explode('/', $path, 2);
    if ($language == $actual_lang) {
        $url = str_replace($path, $lang . '/' . $rest, $url);
    }
}

It's a bit more code, but it should be fairly robust. You could always build a class to do this for you (by parsing, replacing and then rebuilding the URL)...