PHP 获取当前系统版本号

/**
 * 获取当前系统版本号
 * @return mixed|null
 * @throws Exception
 */
function get_version()
{
    static $version = null;
    if ($version) {
        return $version;
    }
    $file = dirname(ROOT_PATH) . '/version.json';
    if (!file_exists($file)) {
        throw new Exception('version.json not found');
    }
    $version = json_decode(file_get_contents($file), true);
    if (!is_array($version)) {
        throw new Exception('version cannot be decoded');
    }
    return $version['version'];
}