Stop writing CLI validation. Parse it right the first time

Very much agree with the article, this is one of the reasons why I wrote Rad [0], which people here might find interesting. The idea is you write CLI scripts with a declarative approach to script arguments, including all the constraints on them, including relational ones. So you don't write your own CLI validation - you declare the shape that args should take, let Rad check user input for you, and you can focus your script on the interesting stuff. For example

  args:
      username str           # Required string
      password str?          # Optional string
      token str?             # Optional auth token
      age int                # Required integer
      status str             # Required string
  
      username requires password     // If username is provided, password must also be provided
      token excludes password        // Token and password cannot be used together
      age range [18, 99]             // Inclusive range from 18 to 99
      status enum ["active", "inactive", "pending"]

Rad will handle all the validation for you, you can just write the rest of your script assuming the constraints you declared are met.

[0]: https://github.com/amterp/rad