function url_exists($url) { 
    $hdrs = @get_headers($url); 
    return is_array($hdrs) ? preg_match('/^HTTP\\/\\d+\\.\\d+\\s+2\\d\\d\\s+.*$/',$hdrs[0]) : false; 
} 
$link1 = 'http://www.site1.com';
$link2= 'http://www.site2.com';
if(url_exists($link1)){
   echo $link1.' var';
}else{
   echo $link1.' yok '.$link2.' bunu dene';
}