For variable doc medium

global_var.rb

# global variable
$count = 0

class Class_var
  # will increase class variable count as soon as class is initiated
  def initialize
    $count += 1
  end
  
  # we dont need this for global var
  def output
    $count
  end
end

# initiate class
object = Class_var.new
object.output  # => 1

# initiate new object
new_object = Class_var.new
new_object.output  # => 2

# we can directly access like this
$count    # => 2