Ruby Reference

Here's a quick Ruby reference. See Learn Ruby for a full tutorial.

Printing in Ruby

To print to output in ruby, use the built-in method print. To print with a newline at the end, use puts.

Strings & Symbols

Strings can be declared with single or double quotes.

word1 = "hello"
word2 = 'hello'

Only double quotes allow interpolation of variables or code.

placeholder = "string interpolation"
"I can use #{placeholder} in double-quoted strings"
#=> "I can use string interpolation in double-quoted strings"

+ is used to concatenate strings together:

"hello " + "world"  #=> "hello world"

Strings in Ruby can be accessed and edited like arrays:

str = "cat"
str[0] #=> "c"

Symbols in Ruby are immutable and are marked with a colon :, like in :word. Symbols are also often used as the keys in hashes.

Arrays and Hashes

Arrays are created with the square bracket syntax [].

arr = [1, 2, 3, 4, 5]
arr[2]  #=> 3
misc_array= [1, "hello", false]

Arrays can be accessed by index from the beginning or end:

arr[-1] #=> 5

Add an item to the end of an array with <<, or or set the value of a specific index:

 arr << 6 #=> [1, 2, 3, 4, 5, 6]
arr[3] = 17
arr[8] = 7 
arr #=> [1, 2, 3, 17, 5, 6, nil, nil, 7]

More methods for getting Array info:

arr.length #=> 6
arr.first #=> 1
arr.include?(3) #=> true

Ranges

Ranges are used for creating ordered sequences and are created with .. syntax:

rang = 1..5
rang.to_a  #=> [1, 2, 3, 4, 5]
arr[1..3] #=> [2, 3, 4]

Hashes

A Hash can be created with the curly-braces {} syntax:

ha = {'color' => 'green', 'number' => 5}
ha.keys #=> ['color', 'number']
ha.values #=> ['green', 5]
hash['price'] = 72 #insertion, with any key

Hashes provide 'instant' lookups, and return nil if the provided key isn't found:

hash['color'] #=> 'green'
hash['missing'] #=> nil

Often, symbols are used as keys, and Ruby provides a shortcut syntax, so these are equivalent:

ha2 = {:color => "blue", :number => 7}
ha2 = {color: "blue", number: 7}
ha2[:color]  #=> "blue"

Both Arrays and Hashes are Enumerable.

Math and Logic

Ruby arithmetic operators:

1 + 1  #=> 2
10 * 2 #=> 20
35 / 5 #=> 7
10.0 / 4.0 #=> 2.5
4 % 3 #=> 1
2 ** 5   #=> 32

Equality and Comparisons

1 == 1 #=> true
2 != 1 #=> true
! true  #=> false
not true  #=> false

Logical Operators

true && true #=> true
false || true #=> true
true and false #=> false
true or false #=> true

Everything in ruby is considered true except for false and nil:

!nil   #=> true
!false #=> true
!1     #=> false
!0     #=> false

An or statement will return the first true value it encounters:

nil || 7          #=> 7
nil || false || 8 #=> 8
1 || 2            #=> 1

Control Structures

If Statement

energy = 4
if energy > 5
  puts "Great!"
elsif energy == 4
  puts "OK"
else
  puts "Uh Oh!"
end

OK

Since energy is 4, the code prints out "OK".

Ruby Loops

While loop example:

counter = 1
while counter <= 5
  puts "iteration #{counter}"
  counter += 1
end

...which prints:

iteration 1
iteration 2
iteration 3
iteration 4
iteration 5

The for loop goes through collections, such as a range, array or hash. This code will produce the same output as the while loop.

for counter in 1..5
  puts "iteration #{counter}"
end

Methods

Here's a basic Ruby method with one parameter:

def double(x)
  x * 2
end

Methods implicitly return the value of the last statement:

double 2 #=> 4  

Multiple Parameters are separated with commas:

def sum(x,y)
  x + y
end

sum 3, 4 #=> 7    

Yield Block

You can pass around pieces of code with a block, which is marked with a do and end.

*(A block is similar to lambdas found in other languages.)

#method that takes block
def take_block
    puts "before block"
    yield
    puts "after block"
end

# call method and pass it a block
take_block do
    puts "i am block"   
end 

This will print out:

before block
i am block
after block

yield calls the block that was passed into the method. Blocks can be surrounded with curly braces {} instead of do and end:

take_block { puts "i am block" }

Each block parameters

Blocks can also take in parameters from the method they are passed to, which is what the each method does:

(1..3).each do |index|
  puts "number #{index}"
end

Output:

number 1
number 2
number 3

each is used by the other ruby collections, such as arrays and hashes:

array.each do |element|
  puts "#{element} is part of the array"
end

hash.each do |key, value|
  puts "#{key} is #{value}"
end

map maps all the items in a collection to new values, e.g. to return an array where each number has been doubled:

 [1, 2, 3, 4].map do |n| 
   n*2
 end
 #=> [2, 4, 6, 8]

This tutorial is based in part on LearnXinYminutes and is licensed under the Creative Commons Attribution-ShareAlike 3.0 License.