PHP validation/regex for URL

$text = preg_replace("
  #((http|https|ftp)://(S*?.S*?))(s|;|)|]|[|{|}|,|"|'|:|<|$|.s)#ie",
  "'<a href="$1" target="_blank">$3</a>$4'",
  $text
);

var_dump(filter_var('example.com', FILTER_VALIDATE_URL));

$pattern = "/b(?:(?:https?|ftp)://|www.)[-a-z0-9+&@#/%?=~_|!:,.;]*[-a-z0-9+&@#/%=~_|]/i";

// Checks if string is a URL
// @param string $url
// @return bool
function isURL($url = NULL) {
	if($url==NULL) return false;

	$protocol = '(http://|https://)';
	$allowed = '([a-z0-9]([-a-z0-9]*[a-z0-9]+)?)';

	$regex = "^". $protocol . // must include the protocol
			 '(' . $allowed . '{1,63}.)+'. // 1 or several sub domains with a max of 63 chars
			 '[a-z]' . '{2,6}'; // followed by a TLD
	if(eregi($regex, $url)==true) return true;
	else return false;
}

function url_exist($url){//se passar a URL existe
    $c=curl_init();
    curl_setopt($c,CURLOPT_URL,$url);
    curl_setopt($c,CURLOPT_HEADER,1);//get the header
    curl_setopt($c,CURLOPT_NOBODY,1);//and *only* get the header
    curl_setopt($c,CURLOPT_RETURNTRANSFER,1);//get the response as a string from curl_exec(), rather than echoing it
    curl_setopt($c,CURLOPT_FRESH_CONNECT,1);//don't use a cached version of the url
    if(!curl_exec($c)){
        //echo $url.' inexists';
        return false;
    }else{
        //echo $url.' exists';
        return true;
    }
    //$httpcode=curl_getinfo($c,CURLINFO_HTTP_CODE);
    //return ($httpcode<400);
}

if (preg_match("#^https?://.+#", $link) and @fopen($link,"r")) echo "OK";

function is_valid_url ($url="") {

        if ($url=="") {
            $url=$this->url;
        }

        $url = @parse_url($url);

        if ( ! $url) {


            return false;
        }

        $url = array_map('trim', $url);
        $url['port'] = (!isset($url['port'])) ? 80 : (int)$url['port'];
        $path = (isset($url['path'])) ? $url['path'] : '';

        if ($path == '') {
            $path = '/';
        }

        $path .= ( isset ( $url['query'] ) ) ? "?$url[query]" : '';



        if ( isset ( $url['host'] ) AND $url['host'] != gethostbyname ( $url['host'] ) ) {
            if ( PHP_VERSION >= 5 ) {
                $headers = get_headers("$url[scheme]://$url[host]:$url[port]$path");
            }
            else {
                $fp = fsockopen($url['host'], $url['port'], $errno, $errstr, 30);

                if ( ! $fp ) {
                    return false;
                }
                fputs($fp, "HEAD $path HTTP/1.1rnHost: $url[host]rnrn");
                $headers = fread ( $fp, 128 );
                fclose ( $fp );
            }
            $headers = ( is_array ( $headers ) ) ? implode ( "n", $headers ) : $headers;
            return ( bool ) preg_match ( '#^HTTP/.*s+[(200|301|302)]+s#i', $headers );
        }

        return false;
    }

^(http://|https://)(([a-z0-9]([-a-z0-9]*[a-z0-9]+)?){1,63}.)+[a-z]{2,6}

(S*?.S*?)

[a-z0-9]

(?i)b((?:https?://|wwwd{0,3}[.]|[a-z0-9.-]+[.][a-z]{2,4}/)(?:[^s()<>]+|(([^s()<>]+|(([^s()<>]+)))*))+(?:(([^s()<>]+|(([^s()<>]+)))*)|[^s`!()[]{};:'".,<>?«»“”‘’]))

preg_match("/(?i)b((?:https?://|wwwd{0,3}[.]|[a-z0-9.-]+[.][a-z]{2,4}/)(?:[^s()<>]+|(([^s()<>]+|(([^s()<>]+)))*))+(?:(([^s()<>]+|(([^s()<>]+)))*)|[^s`!()[]{};:'".,<>?«»“”‘’]))/", $url)

(?xi)
b
(                       # Capture 1: entire matched URL
  (?:
    https?://               # http or https protocol
    |                       #   or
    wwwd{0,3}[.]           # "www.", "www1.", "www2." … "www999."
    |                           #   or
    [a-z0-9.-]+[.][a-z]{2,4}/  # looks like domain name followed by a slash
  )
  (?:                       # One or more:
    [^s()<>]+                  # Run of non-space, non-()<>
    |                           #   or
    (([^s()<>]+|(([^s()<>]+)))*)  # balanced parens, up to 2 levels
  )+
  (?:                       # End with:
    (([^s()<>]+|(([^s()<>]+)))*)  # balanced parens, up to 2 levels
    |                               #   or
    [^s`!()[]{};:'".,<>?«»“”‘’]        # not a space or one of these punct chars
  )
)