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Ruby in Twenty Minutes

Introduction

This is a small Ruby tutorial that should take no more than 20 minutes to complete. It makes the assumption that you already have Ruby installed. (If you don’t have Ruby on your computer download and install it before you get started.)

Interactive Ruby

Ruby comes with a program that will show the results of any Ruby statements you feed it. Playing with Ruby code in interactive sessions like this is a terrific way to learn the language.

Open up IRB (which stands for Interactive Ruby).

  • If you’re using Mac OS X open up Terminal and type irb, then hit enter.
  • If you’re using Linux, open up a shell and type irb and hit enter.
  • If you’re using Windows, open fxri from the Ruby section of your Start Menu.
irb(main):001:0>

Ok, so it’s open. Now what?

Type this: "Hello World"

irb(main):001:0> "Hello World"
=> "Hello World"

Ruby Obeyed You!

What just happened? Did we just write the world’s shortest “Hello World” program? Not exactly. The second line is just IRB’s way of telling us the result of the last expression it evaluated. If we want to print out “Hello World” we need a bit more:

irb(main):002:0> puts "Hello World"
Hello World
=> nil

puts is the basic command to print something out in Ruby. But then what’s the => nil bit? That’s the result of the expression. puts always returns nil, which is Ruby’s absolutely-positively-nothing value.

Your Free Calculator is Here

Already, we have enough to use IRB as a basic calculator:

irb(main):003:0> 3+2
=> 5

Three plus two. Easy enough. What about three times two? You could type it in, it’s short enough, but you may also be able to go up and change what you just entered. Try hitting the up-arrow on your keyboard and see if it brings up the line with 3+2 on it. If it does, you can use the left arrow key to move just after the + sign and then use backspace to change it to a * sign.

irb(main):004:0> 3*2
=> 6

Next, let’s try three squared:

irb(main):005:0> 3**2
=> 9

In Ruby ** is the way you say “to the power of”. But what if you want to go the other way and find the square root of something?

irb(main):006:0> Math.sqrt(9)
=> 3.0

Ok, wait, what was that last one? If you guessed, “it was figuring out the square root of nine,” you’re right. But let’s take a closer look at things. First of all, what’s Math?

Modules Group Code by Topic

Math is a built-in module for mathematics. Modules serve two roles in Ruby. This shows one role: grouping similar methods together under a familiar name. Math also contains methods like sin() and tan().

Next is a dot. What does the dot do? The dot is how you identify the receiver of a message. What’s the message? In this case it’s sqrt(9), which means call the method sqrt, shorthand for “square root” with the parameter of 9.

The result of this method call is the value 3.0. You might notice it’s not just 3. That’s because most of the time the square root of a number won’t be an integer, so the method always returns a floating-point number.

What if we want to remember the result of some of this math? Assign the result to a variable.

irb(main):007:0> a = 3 ** 2
=> 9
irb(main):008:0> b = 4 ** 2
=> 16
irb(main):009:0> Math.sqrt(a+b)
=> 5.0

As great as this is for a calculator, we’re getting away from the traditional Hello World message that beginning tutorials are supposed to focus on… so let’s go back to that.