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Write your own cat, grep and sort. Then learn OOP.

For people who know the basics and want to write bigger programs. You build seven command-line tools, then learn classes, inheritance, polymorphism and interfaces with projects.

Start the first lesson See the plans

Start inPythonJavaScriptJavaC++C#TypeScriptGoKotlinScalaSwiftRust

You type every line A real checker runs your code Nothing to install
Lessons
68
Chapters
4
Languages
11
Level
Beginner
Free lessons
3
Before you start
Variables, loops, lists and functions (the Learn to code path).

What you build

Seven command-line tools

cat, head, wc, grep, uniq, sort and tr, each in four versions.

Object-oriented projects

A bank account, a stack, a shopping cart, a vending machine and tic-tac-toe.

Tools and topics

Syllabus

The Python lessons. The other languages follow the same plan.

01Projects: Command-Line Tools28 lessons
  1. cat 1: Print Linesfree
  2. cat 2: Number Lines (-n)free
  3. cat 3: Show Special Characters (-A)free
  4. cat 4: Join Several Files
  5. head 1: First 10 Lines
  6. head 2: First n Lines
  7. head 3: When n Is Too Big
  8. head 4: Negative n
  9. wc 1: Count Lines
  10. wc 2: Count Words (-w)
  11. wc 3: Count Characters (-c)
  12. wc 4: Choose What to Count
  13. grep 1: Lines That Match
  14. grep 2: Ignore Case (-i)
  15. grep 3: Lines That Don't Match (-v)
  16. grep 4: Whole Words (-w)
  17. uniq 1: Drop Repeated Lines
  18. uniq 2: Count Repeats (-c)
  19. uniq 3: Only Repeated Lines (-d)
  20. uniq 4: Only Unique Lines (-u)
  21. sort 1: Alphabetical Order
  22. sort 2: Reverse Order (-r)
  23. sort 3: Numeric Order (-n)
  24. sort 4: Sort by Column (-k)
  25. tr 1: Swap One Character
  26. tr 2: Translate a Set
  27. tr 3: Delete Characters (-d)
  28. tr 4: Squeeze Repeats (-s)
02Object-Oriented Programming20 lessons
  1. Static Members: Count the Dogs
  2. Access Modifiers
  3. Secret PIN
  4. Getters and Setters
  5. Inheritance
  6. Animal Sounds
  7. Method Overriding
  8. Custom Greeting
  9. Composition: Has-a
  10. Calling the Parent Method
  11. Polymorphism
  12. Pay Everyone
  13. Abstract Classes
  14. Shape Area
  15. Interfaces
  16. Printable Things
  17. Printing Objects
  18. Comparing Objects
  19. Errors and Exceptions
  20. OOP Capstone
03Object-Oriented Programming - Challenges15 lessons
  1. Ticket Numbers
  2. Thermostat
  3. Inventory Item
  4. Product Price
  5. Employees and Managers
  6. Shipping Options
  7. Car and Engine
  8. Shapes
  9. Payment Fees
  10. Notifiers
  11. Book Label
  12. Sort Your Own Objects
  13. Unique Points
  14. Ticket Booking
  15. Playlist
04Projects: Object-Oriented5 lessons
  1. Bank Account (Encapsulation)
  2. Build a Stack
  3. Shopping Cart Classes
  4. Vending Machine
  5. Tic-Tac-Toe Game Class

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LESSON 1

cat 1: Print Lines

3 lessons of this path are free. No card needed.

Start the lesson See the plans