检查字符串中是否有外链

/**
 * all_external_link 检测字符串是否包含外链
 * @param  string  $text 文字
 * @param  string  $host 域名
 * @return boolean       false 有外链 true 无外链
 */
function all_external_link($text = '', $host = '') {
    if (empty($host)) $host = $_SERVER['HTTP_HOST'];
    $reg = '/http(?:s?):\/\/((?:[A-za-z0-9-]+\.)+[A-za-z]{2,4})/';
    preg_match_all($reg, $text, $data);
    $math = $data[1];
    foreach ($math as $value) {
        if($value != $host) return false;
    }
    return true;
}