1.Global Variables
2.Instance Variables

1.Global Variables:

•    They start with a $ sign.
•    If we do not initialize values to global variables , they take a default value of  nil.

Example:

$ global_var = 20      #initialization of global variable
class Global1
  def print_variable
    puts  Global Variable in Global1 is #$global_var
  end
end

class Global2
  def print_variable
    puts Global Variable in Global2 is #$global_var
  end
end

global1obj=global1.new
globalobj.print_variable
global2obj=Global2.new
global2obj.print_variable

Output:
Global Variable in Global1 is 20      #This is the output from Global1 class
Global Variable in Global2 is 20      #This is the output from Global2 class

• As we can see in our example we have initialized the global variable only once and we are using it in multiple classes.
• Global Variable provide us the ease of assigning it only once and use it anywhere in our code.
• Say we you want to use the same value multiple times in your code , you can assign it to global variables which provides reusability.

2.Instance Variables:

•    They start with a @ sign.
•    Like global variables if we do not initialize values to instance variables , they also take a default    value of nil.

Example:

class Instance
   def instance_variable(name, email, address)
      @ins_name=name               #instance variable for name
      @ins_email=email             #instance variable for email 
      @ins_address=address         #instance variable for address
   end
   def instance_display()
      puts "Person Name #@ins_name"
      puts "Person Email #@ins_email"
      puts "Person Address #@ins_address"
    end
end

# Creating Objects for instance variables
inst1=Instance.new("Siddharth", "siddharthsindhi@gmail.com", "Dehradun")
inst2=Instance.new("Gaurav", "gauravjhaldiyal@gmail.com", "Garhwal")

# Calling Methods with instance variables
inst1.instance_display()
inst2.instance_display()

Output:
Person Name Siddharth
Person Email siddharthsindhi@gmail.com
Person Address Dehradun
Person Name Gaurav
Person Email gauravjhaldiyal@gmail.com
Person Address Garhwal

• As we can see in the example , we pass arguments to a function and then create the instance variables  to store the instance of those variables.
• Then we create an object of that class to access the methods of that class and assign values to it's parameters , which are then stored in the instance variable.