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Getting Started

Install

# Debian, Ubuntu
$ sudo apt-get install ruby-full
# Windows
$ winget install RubyInstallerTeam.Ruby
$ brew install ruby # macOS
$ docker run -it --rm ruby:latest # Docker

What is Gemfile and Gemfile.lock

  • Gemfile Is the Bundler (also gem) configuration file that contains the project's gem list (dependencies)
# Specify gem in the Gemfile in the project root directory
ruby '3.1.2'

source 'https://rubygems.org'
gem 'nokogiri'
gem 'rack', '~>3.0.10'
gem 'rspec', :require => 'spec'

Install all gems in Gemfile

bundle install

Solve the problem of Gemfile.lock inconsistency between mac for development and linux for production

bundle lock --add-platform x86_64-linux

Install a specific version of a specific ruby gem

gem install bundler -v 2.4.20
gem install minitest -v 5.22.3

Update gems using Bundler

# Updating a single gem using Bundler
$ bundle update nokogiri
# Use Bundler to update each gem in the Gemfile
$ bundle update

Comment

# This is a single line comments.
=begin
Multi-line
Comment
=end
puts "Hello world!"  # Inline comments for code

reserved words

Reserved words Description
__ENCODING__ The script encoding of the current file
__LINE__ The line number of this keyword in the current file
__FILE__ The path of the current file
BEGIN Code enclosed in { } is run before the program is run
END Code enclosed in { } is run at the end of the program
alias Create an alias for an existing method, operator, or global variable
and Logical AND operator
begin Begin a block of code
break Terminate a loop
case Compare an expression with matching when clauses, terminated with
end
class Define a class
def define a function/method
defined? Check if a variable or function exist
do Start a block of code, terminated with the
end keyword
else Execute the following code if previous conditions are not met
elsif Alternative condition for if expressions
end End blocks of code starting with keywords like begin, class,def,do,if, etc.
ensure Always execute at the end of a block
false Logical boolean value false
for Start a for loop
if Execute the code block if the condition is true
in Used with for loop
module Define a module
next jump to the point before the evaluation of the loop condition
nil Stand for null, invalid, or always false
not Logical NOT operator
or Logical OR operator
redo Jump back to the loop condition evaluation
rescue Evaluate expressions after an exception is raised
retry Repeat method calls when called outside rescue, jump to the top of the block when called inside rescue
return Return a value from a method or block
self Refer to the current object
super Call the same-named method in the superclass
then Used as a separator withif,unless,when,case,rescue
true Logical boolean value true
undef Undefine methods/functions within the current class
until Execute the code block until the condition is false
when Begin a clause under a case statement
while Execute the code block while the condition is true
yield Execute the code block passed to a method

Operator

Logical Operators

  • and
  • or
  • not
  • &&
  • ||
  • !

Bit operators

  • &
  • |
  • ^
  • ~
  • <<
  • >>

Arithmetic operators

  • +
  • -
  • *
  • /
  • %
  • **

Comparison operator

  • ==
  • !=
  • >
  • <
  • >=
  • <=
  • <=>
  • ===
  • eql?
  • equal?

Operator examples

# Addition
1 + 1   #=> 2
# Subtraction
2 - 1   #=> 1
# Multiplication
2 * 2   #=> 4
# Division
10 / 5  #=> 2
17 / 5    #=> 3, not 3.4
17 / 5.0  #=> 3.4
# Exponentiation
2 ** 2  #=> 4
3 ** 4  #=> 81
# Modulus (remainder of division)
8 % 2   #=> 0  (8 / 2 = 4; no remainder)
10 % 4  #=> 2  (10 / 4 = 2 remainder 2)
a = 10
b = 20
a == b #=> false
a != b #=> true
a > b #=> false
a < b #=> true
a >= b #=> false
a <= b #=> true

# Comparison operators
a <=> b #=> -1
c = 20
c <=> b #=> 0
c <=> a  #=> 1
# Equality used in when clauses for case statements
(1...10) === 5 #=> true
# True if the receiver and the argument have the same type and equal values
1.eql?(1.0) #=> false
c = a + b  #=> 30
c += a #=> 40
c -= a #=> 30
c *= a #=> 300
c /= a #=> 30
c %= a #=> 3
c **= a #=> 59049

# Ruby parallel assignment
a = 10
b = 20
c = 30
a, b, c = 10, 20, 30
# Ruby bitwise operators
a = 60
b = 13
# & Binary AND operator copies a bit to the result if it exists in both operands.
a & b #=> 12
# | Binary OR operator copies a bit if it exists in either operand.
a | b #=> 61
# ^ Binary XOR operator copies a bit if it is set in one operand but not both.
a ^ b #=> 49
# ~ Binary Ones Complement is unary and has the effect of 'flipping' bits.
~a
# << Binary Left Shift Operator. The left operand's value is moved
# left by the number of bits specified by the right operand.
a << 2
# >> Binary Right Shift Operator. The left operand's value is moved
# right by the number of bits specified by the right operand.
a >> 2

# Ruby logical operators
a and b #=> true.
a or b #=> true.
a && b #=> true.
(a || b) #=> true.
!(a && b) #=> false.
not(a && b) #=> false.
# Ruby ternary operator
# ? :
# If condition is true ? Then value X : Otherwise value Y
a == 10 ? puts 'Right' : puts 'Wrong'
# Ruby range operators
# .. Creates a range from the start point to the end point (inclusive)
1..10 #=> Creates a range from 1 to 10 (inclusive of 1 and 10)
# ... Creates an exclusive range from the start point to the end point
1...10 #=> Creates an exclusive range from 1 to 10

Operator precedence table

From highest to lowest, this is the precedence table for ruby. High precedence operations happen before low precedence operations.

  • !, ~, unary +
  • **
  • unary -
  • *, /, %
  • +, -
  • <<, >>
  • &
  • |, ^

  • , >=, <, <=

  • <=>, ==, ===, !=, =~, !~
  • &&
  • ||
  • .., ...
  • ?, :
  • modifier-rescue
  • =, +=, -=, etc.
  • defined?
  • not
  • or, and
  • modifier-if, modifier-unless, modifier-while, modifier-until
  • { } blocks

Variables and scope

- - - -
Name Scope Example Explanation
[a-z] or _ Local count = 10 or _count = 10 Local variables must be initialized
@ Instance variable @id = [] Instance variables have a "nil" value before initialization
@@ Class variable @@name = [] Class variables must be initialized
$ Global variable $version = "0.8.9" Global variables have a "nil" value before initialization
[A-Z] Constant PI = 3.14 Constant variables must be initialized, you can change constants, but you will receive a warning

There are five different types of variables. The first character determines the range To read in deap about variables check User Guide cap 19,20,21,22,23 Pre-Defined Variables and Constants

Check the scope of a variable

defined? count
"local-variable"
defined? @id
"instance-variable"
defined? @@name
"class variable"
defined? $version
"global-variable"
defined? PI
"constant"

Data Types

- - - -
Type Example Class Documentation
Integer a = 17 a.class > Integer
a.class.superclass > Numeric		 #
Float a = 87.23 a.class > Float
a.class.superclass > Numeric		 #
String a = "Hello universe" a.class > String #
Array a = [12, 34] a.class > Array #
Hash a = a.class > Hash #
Boolean a = false
a = true		 a.class > FalseClass
a.class > TrueClass		 TrueClass FalseClass
Symbol a = :status a.class > Symbol #
Range a = 1..3 a.class > Range #
Nil a = nil a.class > NilClass #

further reading

Check data type

# Both are synonyms
a = 37
a.kind_of? Integer
# true
a.is_a? Integer
# true

Symbol

week_days = {sunday: 11, monday: 222}

Integer useful methods

2.even?
# true
3.even?
# false

Range

.. Used to create inclusive ranges

range = 1..10
range.to_a
# output => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

... Used to create exclusive ranges

range = 1...10
range.to_a
# output => [1, 2, 3, 4, 5, 6, 7, 8, 9]

some useful methods

Method name Output
cover? (1..5).cover?(5) => true
end ('a'..'z').end => "z"
first (1..5).first => 1
first(3) ('A'..'Z').first(2) => ["A", "B"]
eql? ((0..2).eql?(0..5) => false

Using step in Range

(1..20).step(2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

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