Capstone: todo CLI

The spec

Build a todo tool that runs in the terminal. Four behaviors define the whole project, and everything else is detail.

• Add writes one line of text to a plain file.
• List prints every stored line with a number.
• Done removes one line by its number.
• Missing files and bad numbers report a clear error.

Parse argv

The entry point receives raw command line arguments as a list of strings. Parse them into options and positional args with the standard parser, then match on the result.

{opts, args, _} = OptionParser.parse(argv, switches: [all: :boolean])

Keep parsing thin. Turn argv into a small command value in one place, and let the rest of the program work with that value only.

Plain-text store

One line per todo in a plain text file is enough storage for this project. The file module reads and writes the whole file, which keeps the code short and the format easy to inspect.

path = "todos.txt" File.write!(path, "buy milk\n") items = File.read!(path)

ExUnit for the store

Test the store, not the terminal. Adding then listing covers the core round trip, and a second test covers the empty file edge.

test "saves and lists" do Store.add("milk") assert "milk" in Store.list() end

Next: Capstone: HTTP server

Article author: Arthur Isaev