10 · Project — CLI To-Do App¶

A small end-to-end project combining everything from Level 1: classes, methods, arrays/hashes, string interpolation, blocks, and file persistence.

What you'll build¶

A command-line to-do list that:

Adds tasks
Lists tasks (with done/pending status)
Marks tasks done
Deletes tasks
Persists everything to a JSON file between runs

Project layout¶

todo_app/
    storage.rb
    todo.rb

storage.rb — persistence layer¶

# storage.rb
require "json"

class TaskStorage
  DB_PATH = "tasks.json"

  def self.load
    return [] unless File.exist?(DB_PATH)

    JSON.parse(File.read(DB_PATH), symbolize_names: true)
  rescue JSON::ParserError
    []
  end

  def self.save(tasks)
    File.write(DB_PATH, JSON.pretty_generate(tasks))
  end
end

todo.rb — CLI logic¶

# todo.rb
require_relative "storage"

def add_task(tasks, description)
  tasks << { description: description, done: false }
  puts "Added: #{description}"
end

def list_tasks(tasks)
  if tasks.empty?
    puts "No tasks yet."
    return
  end

  tasks.each_with_index do |task, i|
    status = task[:done] ? "x" : " "
    puts "[#{status}] #{i + 1}. #{task[:description]}"
  end
end

def complete_task(tasks, index)
  task = tasks[index - 1]
  if task.nil?
    puts "No task with number #{index}"
    return
  end
  task[:done] = true
  puts "Marked task #{index} done."
end

def delete_task(tasks, index)
  if index < 1 || index > tasks.length
    puts "No task with number #{index}"
    return
  end
  removed = tasks.delete_at(index - 1)
  puts "Deleted: #{removed[:description]}"
end

tasks = TaskStorage.load
command, *rest = ARGV

if command.nil?
  puts "Usage: ruby todo.rb [add <text> | list | done <n> | delete <n>]"
  exit
end

case command
when "add"
  add_task(tasks, rest.join(" "))
  TaskStorage.save(tasks)
when "list"
  list_tasks(tasks)
when "done"
  complete_task(tasks, rest[0].to_i)
  TaskStorage.save(tasks)
when "delete"
  delete_task(tasks, rest[0].to_i)
  TaskStorage.save(tasks)
else
  puts "Unknown command: #{command}"
end

Running it¶

ruby todo.rb add "Write Level 1 exercises"
ruby todo.rb add "Review Level 2 outline"
ruby todo.rb list
# [ ] 1. Write Level 1 exercises
# [ ] 2. Review Level 2 outline

ruby todo.rb done 1
ruby todo.rb list
# [x] 1. Write Level 1 exercises
# [ ] 2. Review Level 2 outline

How It Actually Works¶

This CLI is a tight loop of three MRI mechanisms you've already met separately: gets.chomp blocks the process on a syscall waiting for stdin data (during which the GIL is released, since blocking I/O never needs the interpreter lock); each parsed command dispatches through ordinary method lookup on your TodoList object; and every @todos << item mutates the same Array object in place rather than allocating a new one, which is why the list persists across loop iterations without you passing it around explicitly — it's held by a single instance variable's reference for the lifetime of the process. When the script exits, that heap and everything on it (including the in-memory todo array) simply disappears, which is exactly why a real version needs the file/database persistence covered in Level 2.

Stretch goals¶

Add a priority field ("low"/"medium"/"high") and sort the list by it before printing.
Add due dates using Ruby's Date class, and highlight overdue tasks.
Add an RSpec test for TaskStorage (you'll formalize this properly with RSpec in Level 2).

Completing this project means you're ready for Level 2 · Intermediate.