新手刚学 Flask，在 pycharm 下敲代码，现在到 E-mail 章无法运行？

D:\Python 3.6\lib\site-packages\flask_sqlalchemy\__init__.py:800: UserWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True to suppress this warning.
  warnings.warn('SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True to suppress this warning.')
usage: hello.py [-?] {shell,db,runserver} ...

positional arguments:
  {shell,db,runserver}
    shell               Runs a Python shell inside Flask application context.
    db                  Perform database migrations
    runserver           Runs the Flask development server i.e. app.run()

optional arguments:
  -?, --help            show this help message and exit

Process finished with exit code 2

有提到需要设置环境变量，但是在 mintty 下设置也报错 无论是

export MAIL_USERNAME=<mail username>或者 set MAIL_USERNAME=<mail username>

报错

bash: syntax error near unexpected tokennewline

我看书是不是漏了啥？

环境变量的设置有没有办法建立临时的？不更改 windows 系统的全局环境变量？ 谢谢各位帮助，祝大家新年快乐！