How to check if a variable is nil in Ruby?

In Ruby, nil is used to indicate that a variable has not been assigned a value or that a method call returned nothing. This article focuses on discussing how to check if a variable is nil in Ruby.

Using nil? method

The nil? method is used to explicitly check if a variable is nil. It returns true if the object isnil, otherwise false.

Syntax:

variable.nil?

Example: 

Below is the Ruby program to check if a variable is nil using nil? method:

Ruby

# Ruby program to check if a variable 
# is nil using nil? method
# Example variable
variable = nil

 if variable.nil?
  puts "Variable is nil"
else
  puts "Variable is not nil"
end

Output

Variable is nil

Explanation:

In this example, we use the nil? method to explicitly check if the variable is nil. If variable is nil, it prints “Variable is nil”, otherwise “Variable is not nil”.

Using == operator

The == operator is used to compare a variable with nil. It returns true if the variable is nil, otherwise false.

Syntax:

variable == nil

Example: 

Below is the Ruby program to check if a variable is nil using == operator.

Ruby

# Ruby program to check if a variable 
# is nil using == operator
# Example variable
variable = nil

if variable == nil
  puts "Variable is nil"
else
  puts "Variable is not nil"
end

Output

Variable is nil

Explanation:

In this example, the == operator compares variable with nil. If variable is equal to nil, it prints “Variable is nil”, otherwise “Variable is not nil”.

Using unless statement

The unless statement is the opposite of the if statement. It executes a block of code if the condition evaluates to false or nil.

Syntax:

unless variable

# Code to execute if variable is nil

end

Example: 

Below is the Ruby program to check if a variable is nil using unless statement:

Ruby

# Ruby program to check if a variable 
# is nil using unless statement
# Example variable
variable = nil
 
unless variable
  puts "Variable is nil"
else
  puts "Variable is not nil"
end

Output

Variable is nil

Explanation:

In this example we use unless statement to execute a block of code if variable evaluates to false or nil. If variable is nil, it prints “Variable is nil”, otherwise “Variable is not nil”.