Learn to Code with Ruby:
The Command Line


The Command Line

  • the TERMINAL is a window into which you can talk directly to your computer
    • aka console or command line or command prompt or shell
  • very low level, based entirely on text and typing, not graphics and mousing
  • when you type into the terminal, you are always issuing COMMANDS
    • which is why it's called the Command Line

Opening the Terminal

  • to open your terminal:
    • Mac OS: launch the "Terminal" application
    • Windows with Railsinstaller: launch "Command Prompt with Ruby and Rails"
  • Important: make your terminal as tall as possible


  • a DIRECTORY is a location on your hard disk
    • also called a FOLDER
  • directories can contain FILES
  • directories can also contain other directories (called SUBDIRECTORIES)

The Current Directory

  • inside the Terminal, you are always inside a directory
  • it is very important not to get lost! You must try to remember which directory you are in.
  • If you forget, you can use a special command called pwd

Home Directory

  • when you open the Terminal you are in your HOME DIRECTORY
  • usually you don't want to store files directly in here

Listing Directory Contents

  • when you type ls ("list") it shows the contents of the current directory

Making a directory

  • when you type mkdir ("make dir") it creates a new SUBDIRECTORY inside the current directory

    mkdir code

Changing directories

  • cd ("change dir") moves you into a different directory
  • For example, cd code would move you into a directory named code
  • If you ever get lost, type cd all on its own and press the return key. This will send you back to your home directory.

Basic Command Line Glossary

  • pwd ("print working dir") -- shows the name of the current directory
  • ls ("list") -- shows the contents of the current directory
  • mkdir ("make dir") -- creates a new SUBDIRECTORY inside the current directory
  • cd ("change dir") -- move into a different directory
  • touch whatever.txt -- creates an empty file named whatever.txt inside the current directory

LAB: make a subdirectory and then enter it

  1. open Terminal
  2. make a new subdirectory using mkdir code
  3. change into that directory using cd code
  4. list its contents using ls (and note that it's empty)


  • a file is a place on disk for storing stuff
  • "stuff" here could be anything at all
    • documents, pictures, sounds, applications...
  • every file lives inside a directory

Text Editor

  • a text editor is a program that edits a text file
  • a text editor is like a word processor
  • but a text editor is not a word processor
  • You probably have Sublime Text
    • others include TextMate, Notepad++
    • but NOT TextEdit or Notepad or Microsoft Word

Source File

  • source code is the essence of a program
  • source files are text files that contain source code
  • to RUN a program you type ruby and then the name of the source file

  • The Recipe Metaphor

    • source file = recipe
    • running = cooking

LAB: Hello, World

  1. Make sure you are in your code subdirectory using pwd
  2. Create a file named hello.rb using touch hello.rb
  3. Open hello.rb in your favorite text editor
  4. Inside this file, put the following source code:

    puts "Hello, World!"
  5. Save the file

  6. Go back to the terminal

  7. Run this file using ruby hello.rb

What happens? Is this what you expected?


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