$string = "hello how are you www.google.com";
$string = explode(" ", $string);
foreach ($string as $word){
if ( (strpos($word, "http://") === 0) || (strpos($word, "www.") === 0) ){
// Code you want to excute if string is a link
}

}


yada


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

// The Text you want to filter for urls
$text = "The text you want to filter goes here. http://google.com";

// Check if there is a url in the text
if(preg_match($reg_exUrl, $text, $url)) {

// make the urls hyper links
echo preg_replace($reg_exUrl, "<a href="{$url[0]}">{$url[0]}</a> ", $text);

} else {

// if no urls in the text just return the text
echo $text;

}

test etmedim ama bunlar fikir verebilir