How do I linkify Twitter usernames using PHP preg_replace?

Question

I want to search the text property of my twitter status objects and swap out @username for <a href="http:/twitter.com/username">@username</a>. What I have tried so far looks like this:

$pattern = '/([@]{1})([a-zA-Z0-9\_]+)/';
$replace = '<a href="http://twitter.com/\2"&gt;\1\2&lt;/a&gt;';
$new_string = preg_replace($pattern, $replace, $text);

But it doesn't do any replacements. I know my reg exp is wrong but I can't figure out exactly where/why. Help?

**Edit: ... sample data as requested?

$text = '@janesmith I like that, but my friend @johndoe said it better.';

Desired output:

@janesmith I like that, but my friend @johndoe said it better.

***** MY FULL FUNCTION *****

function linkify($string, $twitter=false) {

    // reg exp pattern
    $pattern = "/(http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(\/\S*)?/";

    // convert string URLs to active links
    $new_string = preg_replace($pattern, "<a href=\"\\0\">\\0</a>", $string);

    if ($twitter) {
        $pattern = '/@([a-zA-Z0-9_]+)/';
        $replace = '<a href="http://twitter.com/\1"&gt;@\1&lt;/a&gt;';
        $new_string = preg_replace($pattern, $replace, $new_string);
    }

    return $new_string;
}

Answer 1

Why is the \ there before _? Does it work if you take out the \? Though that shouldn't have broken the functionality...

It might be helpful to change the \1 to \\1 so that you're sure the backslash is escaped; or better (since PHP 4.0.4) $1. But again, it should have worked as-is, within single quotes.

Also, you can simplify:

$pattern = '/@([a-zA-Z0-9_]+)/';
$replace = '<a href="http://twitter.com/$1"&gt;@$1&lt;/a&gt;';