when you create a template using cli3 (select vue-router), an environment variable of  process.env.BASE_URL  is used in  router.js . 
 I looked up the documentation for ide/mode-and-env.html-sharp%E6%A8%A1%E5%BC%8F" rel=" nofollow noreferrer "> vue-cli3 environment variables and patterns , and found that you can only use environment variables that start with  VUE_APP_  (which can be used in runnable code). 
 what should I do if I want to change the  process.env.BASE_URL  environment variable according to the pattern? 
 what if I don"t want to use the environment variable that starts with  VUE_APP_ ? 
