Any plain, lowercase word is a variable in ruby. Variables may consist of letters, digits and underscores.

x, y, banana2, or phone_a_quail are examples.

Variables are like nicknames. Remember when everyone used to call you Stinky Pete? People would say, “Get over here, Stinky Pete!” And everyone miraculously knew that Stinky Pete was you.

With variables, you give a nickname to something you use frequently. For instance, let’s say you run an orphanage. It’s a mean orphanage. And whenever Daddy Warbucks comes to buy more kids, we insist that he pay us one-hundred twenty-one dollars and eight cents for the kid’s teddy bear, which the kid has become attached to over in the darker moments of living in such nightmarish custody.

teddy_bear_fee = 121.08

Later, when you ring him up at the cash register (a really souped-up cash register which runs Ruby!), you’ll need to add together all his charges into a total.

total = orphan_fee + teddy_bear_fee + gratuity

Those variable nicknames sure help. And in the seedy underground of child sales, any help is appreciated I’m sure.


The most basic type of number is an integer, a series of digits that can start with a plus or minus sign.

1, 23, and -10000 are examples.

Commas are not allowed in numbers, but underscores are. So if you feel the need to mark your thousands so the numbers are more readable, use an underscore.

population = 12_000_000_000

Decimal numbers are called floats in Ruby. Floats consist of numbers with a decimal place or scientific notation.

3.14, -808.08 and 12.043e-04 are examples.


Strings are any sort of characters (letters, digits, punctuation) surrounded by quotes. Both single and double quotes are used to create strings.

"sealab", '2021', or "These cartoons are hilarious!" are examples.

When you enclose characters in quotes, they are stored together as a single string.

Think of a reporter who is jotting down the mouthnoises of a rambling celebrity. “I’m a lot wiser,” says Avril Lavigne. “Now I know what the business is like—what you have to do and how to work it.”

 avril_quote = "I'm a lot wiser.  Now I know 
  what the business is like -- what you have 
  to do and how to work it."

So, just as we stored a number in the teddy_bear_fee variable, now we’re storing a collection of characters (a string) in the avril_quote variable. The reporter sends this quote to the printers, who just happen to use Ruby to operate their printing press.

 print oprah_quote

 print avril_quote
 print ashlee_simpson_debacle


Symbols are words that look just like variables. Again, they may contain letters, digits, or underscores. But they start with a colon.

:a, :b, or :ponce_de_leon are examples.

Symbols are lightweight strings. Usually, symbols are used in situations where you need a string but you won’t be printing it to the screen.

You could say a symbol is a bit easier on the computer. It’s like an antacid. The colon indicates the bubbles trickling up from your computer’s stomach as it digests the symbol. Ah. Sweet, sweet relief.


Constants are words like variables, but constants are capitalized. If variables are the nouns of Ruby, then think of constants as the proper nouns.

Time, Array or Bunny_Lake_is_Missing are examples.

In English, proper nouns are capitalized. The Empire State Building. You can’t just move the Empire State Building. You can’t just decide that the Empire State Building is something else. Proper nouns are like that. They refer to something very specific and usually don’t change over time.

In the same way, constants can’t be changed after they are set.

EmpireStateBuilding = "350 5th Avenue, NYC, NY"

If we try to change the constant, Ruby will complain to us. Such things are frowned upon.


If variables and constants are the nouns, then methods are the verbs. Methods are usually attached to the end of variables and constants by a dot. You’ve already seen methods at work.

In the above, open is the method. It is the action, the verb. In some cases, you’ll see actions chained together.

We’ve instructed the computer to open the front door and then immediately close it.


The above is an action as well. We’re instructing the computer to test the door to see if it’s open. The method could be called Door.test_to_see_if_its_open, but the is_open? name is succinct and just as correct. Both exclamation marks and question marks may be used in method names.

Method Arguments

A method may require more information in order to perform its action. If we want the computer to paint the door, we should provide a color as well.

Method arguments are attached to the end of a method. The arguments are usually surrounded by parentheses and separated by commas.

front_door.paint( 3, :red )

The above paints the front door three coats of red.

Think of it as an inner tube the method is pulling along, containing its extra instructions. The parentheses form the wet, round edges of the inner tube. The commas are the feet of each argument, sticking over the edge. The last argument has its feet tucked under so they don’t show.

Like a boat pulling many inner tubes, methods with arguments can be chained.

front_door.paint( 3, :red ).dry( 30 ).close()

The above paints the front door three coats of red, dries for 30 minutes, and closes the door. Even though the last method has no arguments, you can still use parentheses if you like. There is no use dragging an empty inner tube, so the parentheses are normally dropped.

Some methods (such as print) are kernel methods. These methods are used throughout Ruby. Since they are so common, you won’t use the dot.

print "See, no dot."

Class Methods

Like the methods described above (also called instance methods), class methods are usually attached after variables and constants. Rather than a dot, a double colon is used.

Door::new( :oak )

As seen here, the new class method is most often used to create things. In the above example, we’re asking Ruby to make a new oak door for us. Of course, Ruby has to have an understanding of how to make a door—as well as a wealth of timber, lumberjacks, and those long, wiggily, two-man saws.


Global Variables

Variables which begin with a dollar sign are global.

$x, $1, $chunky and $CHunKY_bACOn are examples.

Most variables are rather temporary in nature. Some parts of your program are like little houses. You walk in and they have their own variables. In one house, you may have a dad that represents Archie, a travelling salesman and skeleton collector. In another house, dad could represent Peter, a lion tamer with a great love for flannel. Each house has its own meaning for dad.

With global variables, you can be guaranteed that the variable is the same in every little house. The dollar sign is very appropriate. Every American home respects the value of the dollar. We’re crazy for the stuff. Try knocking on any door in America and hand them cash. I can guarantee you won’t get the same reaction if you knock on a door and offer up Peter, a lion tamer with a great love for flannel.

Global variables can be used anywhere in your program. They never go out of sight.

Instance Variables

Variables that begin with an at symbol are instance variables.

@x, @y, and @only_the_chunkiest_cut_of_bacon_I_have_ever_seen are examples.

These variables are often used to define the attributes of something. For example, you might provide Ruby with the width of the front_door by setting the @width variable inside that front_door. Instance variables are used to define characteristics of a single object in Ruby.

Think of the at symbol as meaning attribute.

Class variables

Variables that begin with double at symbols are class variables.

@@x, @@y, and @@i_will_take_your_chunky_bacon_and_raise_you_two are examples.

Class variables, too, are used to define attributes. But rather than defining an attribute for a single object in Ruby, class variables give an attribute to many related objects in Ruby. If instance variables set attributes for a single front_door, then class variables set attributes for everything that is a Door.

Think of the double at prefix as meaning attribute all. Additionally, you can think of a swarm of AT-ATs from Star Wars, which are all commanded by Ruby. You change a class variable and not just one changes, they all change.



Any code surrounded by curly braces is a block.

2.times { print "Yes, I've used chunky bacon in my examples, but never again!" } is an example.

With blocks, you can group a set of instructions together so that they can be passed around your program. The curly braces give the appearance of crab pincers that have snatched the code and are holding it together. When you see these two pincers, remember that the code inside has been pressed into a single unit.

It’s like one of those little Hello Kitty boxes they sell at the mall that’s stuffed with tiny pencils and microscopic paper, all crammed into a glittery transparent case that can be concealed in your palm for covert stationary operations. Except that blocks don’t require so much squinting.

The curly braces can also be traded for the words do and end, which is nice if your block is longer than one line.

 loop do
   print "Much better." 
   print "Ah.  More space!" 
   print "My back was killin' me in those crab pincers." 

Block Arguments

Block arguments are a set of variables surrounded by pipe characters and separated by commas.

|x|, |x,y|, and |up, down, all_around| are examples.

Block arguments are used at the beginning of a block.

{ |x,y| x + y }

In the above example, |x,y| are the arguments. After the arguments, we have a bit of code. The expression x + y adds the two arguments together.

I like to think of the pipe characters as representing a tunnel. They give the appearance of a chute that the variables are sliding down. (An x goes down spread eagle, while the y neatly crosses her legs.) This chute acts as a passageway between blocks and the world around them.

Variables are passed through this chute (or tunnel) into the block.


A range is two values surrounded by parentheses and separated by an ellipsis (in the form of two or three dots).

(1..3) is a range, representing the numbers 1 through 3.

('a'..'z') is a range, representing a lowercase alphabet.

Think of it as an accordion that has been squeezed down for carrying. (Sure, you can build a great sense of self-worth by carrying around an unfolded accordion, but sometimes a person needs to wallow in self-doubt, carefully concealing the squeeze-box.) The parentheses are the handles on the sides of a smaller, handheld accordion. The dots are the chain, keeping the folds tightly closed.

Normally, only two dots are used. If a third dot is used, the last value in the range is excluded.

(0...5) represents the numbers 0 through 4.

When you see that third dot, imagine opening the accordion slightly. Just enough to let one note from its chamber. The note is that end value. We’ll let the sky eat it.


An array is a list surrounded by square brackets and separated by commas.

[1, 2, 3] is an array of numbers.

['coat', 'mittens', 'snowboard'] is an array of strings.

Think of it as a caterpillar that has been stapled into your code. The two square brackets are staples which keep the caterpillar from moving, so you can keep track of that end is the head and which is the tail. The commas are the caterpillar’s legs, wiggling between each section of its body.

Once there was a caterpillar who had commas for legs. Which meant he had to allow a literary pause after each step. The other caterpillars really respected him for it and he came to have quite a commanding presence. Oh, and talk about a philanthropist! He was notorious for giving fresh leaves to those less-fortunate.

Yes, an array is a collection of things, but it also keeps those things in a specific order.


A hash is a dictionary surrounded by curly braces. Dictionaries match words with their definitions. Ruby does so with arrows made from an equals sign, followed by a greater-than sign.

{'a' => 'aardvark', 'b' => 'badger'} is an example.

This time, the curly braces represent little book symbols. See how they look like little, open books with creases down the middle? They represent opening and closing our dictionary.

Imagine our dictionary has a definition on each of its pages. The commas represent the corner of each page, which we turn to see the next definition. And on each page: a word followed by an arrow pointing to the definition.


   'name' => 'Peter',
   'profession' => 'lion tamer',

   'great love' => 'flannel'

I’m not comparing hashes to dictionaries because you can only store definitions in a hash. In the example above, I stored personal information for Peter, the lion tamer with a great love for flannel. Hashes are like dictionaries because they can be very easy to search through.

Unlike arrays, the items in a hash are not kept in a specific order.

Regular Expressions

A regular expression (or regexp) is a set of characters surrounded by slashes.

/ruby/, /[0-9]+/ and /^\d{3}-\d{3}-\d{4}/ are examples.

Regular expressions are used to find words or patterns in text. The slashes on each side of the expression are pins.

Imagine if you had a little word with pins on both side and you held it over a book. You pass the word over the book and when it gets near a matching word, it starts blinking. You pin the regular expression onto the book, right over the match and it glows with the letters of the matching word.

Oh, and when you poke the pins into the book, the paper sneezes, reg-exp!

Regular expressions are much faster than passing your hand over pages of a book. Ruby can use a regular expression to search volumes of books very quickly.


You’ll use the following list of operators to do math in Ruby or to compare things. Scan over the list, recognize a few. You know, addition + and subtraction - and so on.

  ** !  ~  *  /  %  +  -  &  
  << >> |  ^  >  >= <  <= <=>
  || != =~ !~ && += -= == ===
  .. ... not and or          


Ruby has a number of built-in words, imbued with meaning. These words cannot be used as variables or changed to suit your purposes. Some of these we’ve already discussed. They are in the safe house, my friend. You touch these and you’ll be served an official syntax error.

  alias   and     BEGIN   begin   break   case    class   def     defined 
  do      else    elsif   END     end     ensure  false   for     if 
  in      module  next    nil     not     or      redo    rescue  retry 
  return  self    super   then    true    undef   unless  until   when 
  while   yield 

Good enough. These are the illustrious members of the Ruby language. We’ll be having quite the junket for the next three chapters, gluing these parts together into sly bits of (poignant) code.

I’d recommend skimming all of the parts of speech once again. Give yourself a broad view of them. I’ll be testing your mettle in the next section.