PHP - Add link to a URL in a string

Question

I have a function that will add the <a href> tag before a link and </a> after the link. However, it breaks for some webpages. How would you improve this function? Thanks!

function processString($s) 
{
    // check if there is a link

    if(preg_match("/http:\/\//",$s))
    {
        print preg_match("/http:\/\//",$s);


        $startUrl =  stripos($s,"http://");

        // if the link is in between text
        if(stripos($s," ",$startUrl)){
            $endUrl = stripos($s," ",$startUrl);
        }
        // if link is at the end of string
        else {$endUrl = strlen($s);}

        $beforeUrl = substr($s,0,$startUrl);
        $url = substr($s,$startUrl,$endUrl-$startUrl);
        $afterUrl = substr($s,$endUrl);

        $newString = $beforeUrl."<a href=\"$url\">".$url."</a>".$afterUrl;

        return $newString;
    }

    return $s;
}

Answer 1

function processString($s) {
    return preg_replace('/https?:\/\/[\w\-\.!~#?&=+\*\'"(),\/]+/','<a href="$0">$0</a>',$s);
}

Answer 2

It breaks for all URLs that contain "special" HTML characters. To be safe, pass the three string components through htmlspecialchars() before concatenating them together (unless you want to allow HTML outside the URL).

Answer 3

function processString($s){
  return preg_replace('@((https?://)?([-\w]+\.[-\w\.]+)+\w(:\d+)?(/([-\w/_\.]*(\?\S+)?)?)*)@', '<a href="$1">$1</a>', $s);
}

Found it here