Defining the To-Do API

Unlike with a graphical program, the user of a CLI tool generally provides all the input and parameters required for the tool to work upfront. The tool uses that input to do its job and provides the results back to the user as text output on the screen. When an error occurs, a CLI tool usually provides details about it in a way that’s easy and practical for the user to understand or potentially filter out.

Managing a to-do list

In this chapter, we’ll get comfortable working with input and output as we build a command-line tool for managing a list of to-do items. This tool will let us keep track of items left in a project or activity. The tool will save the list of items in a file using the JSON format.

To implement this tool, we’ll accept input data from our users in a variety of ways. We’ll get input from standard input (STDIN) and command-line parameters. We’ll also use environment ...