phpseclib\Net\SFTP::_realpath PHP Method

    function _realpath($path)
    {
        if ($this->pwd === false) {
            // http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-8.9
            if (!$this->_send_sftp_packet(NET_SFTP_REALPATH, pack('Na*', strlen($path), $path))) {
                return false;
            }
            $response = $this->_get_sftp_packet();
            switch ($this->packet_type) {
                case NET_SFTP_NAME:
                    // although SSH_FXP_NAME is implemented differently in SFTPv3 than it is in SFTPv4+, the following
                    // should work on all SFTP versions since the only part of the SSH_FXP_NAME packet the following looks
                    // at is the first part and that part is defined the same in SFTP versions 3 through 6.
                    Strings::shift($response, 4);
                    // skip over the count - it should be 1, anyway
                    if (strlen($response) < 4) {
                        return false;
                    }
                    extract(unpack('Nlength', Strings::shift($response, 4)));
                    return Strings::shift($response, $length);
                case NET_SFTP_STATUS:
                    $this->_logError($response);
                    return false;
                default:
                    throw new \UnexpectedValueException('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
            }
        }
        if ($path[0] != '/') {
            $path = $this->pwd . '/' . $path;
        }
        $path = explode('/', $path);
        $new = array();
        foreach ($path as $dir) {
            if (!strlen($dir)) {
                continue;
            }
            switch ($dir) {
                case '..':
                    array_pop($new);
                case '.':
                    break;
                default:
                    $new[] = $dir;
            }
        }
        return '/' . implode('/', $new);
    }