public function binaryVersion()
    {
        if (!self::$version) {
            if (0 === $this->process->execute('svn --version', $output)) {
                if (preg_match('{(\d+(?:\.\d+)+)}', $output, $match)) {
                    self::$version = $match[1];
                }
            }
        }

        return self::$version;
    }