Powerful Command-Line Applications in Go

Increasing Flexibility with Environment Variables

With all the improvements you made to your to-do tool so far, you’ve provided your users with several useful features. But the user still can’t select which file to save to the list of to-do items. You could use different approaches in this situation, such as adding another flag to allow the user to specify the file name, but another way to make your tool more flexible is by using environment variables.

Using environment variables allows your users to specify options once in their shell configuration, which means the user avoids typing that option for every command execution. It also lets the user have different configurations for different environments.

In Go, the os package provides functions ...