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Ruby is an open source server-side scripting language for object-oriented programming, designed and developed in the mid-1990s by Yukihiro Matsumoto of Japan. In the Ruby community, Matsumoto is also known as Matz. Ruby runs on multiple platforms, such as Windows, Mac OS, and various versions of UNIX.

A variable is a storage location that holds any data that can be used by any program.

Ruby supports five types of variables.

1. Generally lowercase letters, underscore beginning: Variable.

2.$ Start with: Global variable.

3.@ Start: Instance variable.

4.@@ Class variables are shared throughout the inheritance chain.

5. Capital letters begin with: Constant.

Ruby global variables

Global variables start with $. An uninitialized global variable has a value of nil and generates a warning when the-w option is used.

Assigning values to global variables changes the global state, so global variables are not recommended.

The following example shows the use of global variables.

examples

#!/ usr/bin/ruby# -*- coding: UTF-8 -*- $global_variable = 10class Class1 def print_global puts "global variable output in Class1 is #$global_variable" endclass 2 def print_global puts "global variable" ends class1obj = Class1.newclass1obj.print_globalclass2obj = Class2.newclass2obj.print_global in Class2

$global_variable is a global variable. This will produce the following results:

Note: In Ruby, you can access the value of any variable or constant by placing the #character in front of it.

Global variables output 10 in Class1 Global variables output 10 in Class2

Ruby instance variables

Instance variables start with @. An uninitialized instance variable has a value of nil, which generates a warning when the-w option is used.

The following example shows the usage of instance variables.

examples

#!/ usr/bin/ruby class Customer def initialize(id, name, addr) @cust_id=id @cust_name=name @cust_addr=addr end def display_details() puts "Customer id #@cust_id" puts "Customer name #@cust_name" puts "Customer address #@cust_addr" end #Create object cusst1 =Customer.new("1", "John", "Wisdom Apartments, Ludhiya") cusst2 =Customer.new("2", "Poul", "New Empire road, Khandala") #Call method custom1.display_details () custom2.display_details ()

Here,@cust_id,@cust_name, and @cust_addr are instance variables. This will produce the following results:

Customer id 1Customer name JohnCustomer address Wisdom Apartments, LudhiyaCustomer id 2Customer name PoulCustomer address New Empire road, Khandala

Ruby class variables

Class variables start with @@ and must be initialized before they can be used in method definitions.

Referring to an uninitialized class variable generates an error. A class variable can be shared among subclasses or submodules of the class or module that defines it.

Overloaded class variables generate warnings when the-w option is used.

The following example shows the use of class variables.

examples

#!/ usr/bin/ruby class Customer @@no_of_customers=0 def initialize(id, name, addr) @cust_id=id @cust_name=name @cust_addr=addr end def display_details() puts "Customer id #@cust_id" puts "Customer name #@cust_name" puts "Customer address #@cust_addr" end def total_no_of_customers() @@no_of_customers += 1 puts "Total number of customers: #@@no_of_customers" end #Create object cusst1 =Customer.new("1", "John", "Wisdom Apartments, Ludhiya") cusst2 =Customer.new("2", "Poul", "New Empire road, Khandala") #Call method custom1.total_no_of_customers () custom2.total_no_of_customers ()

Here,@@no_of_customers is a class variable. This will produce the following results:

Total number of customers: 1Total number of customers: 2

Ruby local variables

Local variables begin with a lowercase letter or underscore_. The scope of a local variable is from class, module, def, or do to the corresponding end or from the left brace to the right brace {}.

When an uninitialized local variable is called, it is interpreted as calling a method with no arguments.

Assignment to an uninitialized local variable can also be treated as a variable declaration. The variable exists until the end of the current domain. The life cycle of local variables is determined when Ruby parses the program.

In the example above, the local variables are id, name, and addr.

Ruby constant

Constants begin with capital letters. Constants defined within a class or module can be accessed from within the class or module, and constants defined outside the class or module can be accessed globally.

Constants cannot be defined inside methods. Referring to an uninitialized constant generates an error. Assigning a value to an initialized constant generates a warning.

examples

#!/ usr/bin/ruby# -*- coding: UTF-8 -*- class Example VAR1 = 100 VAR2 = 200 def show puts "The value of the first constant is #{VAR1}" puts "The value of the second constant is #{VAR2}" endend #create object=Example.new()object.show

Here, VAR1 and VAR2 are constants. This will produce the following results:

The first constant has a value of 100 and the second constant has a value of 200.

Ruby pseudovariable

They are special variables that have the appearance of local variables but behave like constants. You cannot assign any value to these variables.

1.self: The receiver object of the current method.

2.true: represents the value of true.

3.false: represents the value of false.

4.nil: Represents undefined value.

5.__ FILE__: The name of the current source file.

6.__ LINE__: The number of the current line in the source file.

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