How do I linkify urls in a string with php

"Look on http://www.google.com".

$string = "Look on http://www.google.com"
$new_string = ereg_replace("[[:alpha:]]+://[^<>[:space:]]+[[:alnum:]/]","<a href="\0">\0</a>", $string);

$text = preg_replace('@(https?://([-w.]+)+(:d+)?(/([w/_.]*(?S+)?)?)?)@', '<a href="$1">$1</a>', $text);

<?php
// The Regular Expression filter
$pattern = "/(http|https|ftp|ftps)://[a-zA-Z0-9-.]+.[a-zA-Z]{2,3}(/S*)?/";

//example text
$text="Example user text with a URL http://www.zero7web.com , second link http://www.didsburydesign.co.uk";

// convert URLs into Links
$text= preg_replace($pattern, "<a href="\0" rel="nofollow">\0</a>", $text);

echo $text;
?>

$result = preg_replace('/b(https?|ftp|file)://[-A-Z0-9+&@#/%?=~_|!:,.;]*[A-Z0-9+&@#/%=~_|]/i', '<a href=""></a>', $text);

<?

   function link_it($text)
   {
        $text= preg_replace("/(^|[n ])([w]*?)([w]*?://[w]+[^ ,"nrt<]*)/is", "$1$2<a href="$3" >$3</a>", $text);
        $text= preg_replace("/(^|[n ])([w]*?)((www).[^ ,"tnr<]*)/is", "$1$2<a href="http://$3" >$3</a>", $text);
                $text= preg_replace("/(^|[n ])([w]*?)((ftp).[^ ,"tnr<]*)/is", "$1$2<a href="ftp://$3" >$3</a>", $text);
        $text= preg_replace("/(^|[n ])([a-z0-9&-_.]+?)@([w-]+.([w-.]+)+)/i", "$1<a href="mailto:$2@$3">$2@$3</a>", $text);
        return($text);
    }


$text = "ini link gue: http://sapua.com <br>
https://sapua.com <br>
anything1://www.sss.com <br>

dua www.google.com <br>
tiga http://www.google.com <br>

ftp.sapua.com <br>

someone@sapua.com


";

print link_it($text);

?>