Kon’nichi wa, Ruby — Why's (Poignant) Guide to Ruby

Open your text editor. Any text editor. Type the following line and save it as chunky.rb:

print "Chunky bacon!"

Now open your terminal and run it:

$ ruby chunky.rb
Chunky bacon!

There. Chunky bacon. Your first Ruby program. The only thing that line does is print a string to the screen. But that’s not nothing. That’s everything.

Numbers

5          # an integer
3.14       # a floating point number
2_000_000  # underscores make large numbers readable

In Ruby, everything is an object. Even numbers. That means numbers have methods:

5.to_s      # => "5"   (converts to string)
5.times { puts "hello" }  # prints "hello" five times

Strings

"hello, world"      # double-quoted string
'single-quoted'     # single-quoted — no interpolation
"chunky #{1 + 1}"  # => "chunky 2" — interpolation with #{}

String interpolation with #{} is one of Ruby’s most useful features. Any Ruby expression inside #{} gets evaluated and inserted into the string.

Variables

name = "Trady Blix"
age  = 9
name  # => "Trady Blix"
age   # => 9

Variables in Ruby start with a lowercase letter or underscore. You don’t declare types. The variable just takes on whatever value you assign.

String Methods

name = "trady blix"
name.upcase        # => "TRADY BLIX"
name.length        # => 10
name.reverse       # => "xilb ydart"
name.include?("blix")  # => true
name.split(" ")    # => ["trady", "blix"]
name.capitalize    # => "Trady blix"

Getting Input

print "What is your name? "
name = gets.chomp
puts "Hello, #{name}!"

gets reads a line of input from the user. chomp removes the trailing newline character that gets includes.

Conditionals

age = 9
if age > 10
  puts "old enough"
elsif age == 9
  puts "exactly nine"
else
  puts "younger"
end

Ruby also has a one-line conditional form:

puts "hello" if name == "Trady Blix"
puts "goodbye" unless name == "Trady Blix"