Predefined Constants in Ruby Language

Ruby is a versatile and dynamic programming language known for its flexibility and readability. To make coding

more efficient and readable, Ruby provides a set of predefined constants. These constants are built-in values that can be accessed throughout your Ruby programs without the need for explicit declaration. In this article, we’ll explore some of the most commonly used predefined constants in Ruby, along with examples of how to use them.

1. true and false

Ruby’s true and false constants represent boolean values. They are used extensively for logical operations and conditional statements.

is_ruby_fun = true
is_python_fun = false

if is_ruby_fun
  puts "Ruby is fun!"
else
  puts "Ruby is not fun."
end

2. nil

nil represents the absence of a value, similar to null in other programming languages. It is often used to indicate the absence of data or an uninitialized variable.

my_variable = nil

if my_variable.nil?
  puts "The variable is nil."
else
  puts "The variable has a value."
end

3. STDIN, STDOUT, and STDERR

These constants represent the standard input, standard output, and standard error streams, respectively. They are used for interacting with the command line.

puts "Enter your name: "
name = STDIN.gets.chomp
STDOUT.puts "Hello, #{name}!"
STDERR.puts "This is an error message."

4. PI

Math::PI is a predefined constant representing the mathematical constant Pi (π). It is part of the Math module.

radius = 5
circumference = 2 * Math::PI * radius
puts "The circumference of a circle with a radius of #{radius} is #{circumference}."

5. RUBY_VERSION and RUBY_PLATFORM

These constants provide information about the Ruby environment. RUBY_VERSION gives the current Ruby version, while RUBY_PLATFORM indicates the platform on which Ruby is running.

puts "Running Ruby version #{RUBY_VERSION} on #{RUBY_PLATFORM}."

6. ARGV

ARGV is an array containing command-line arguments passed to a Ruby script. It is especially useful for building command-line utilities.

puts "You provided the following arguments:"
ARGV.each do |arg|
  puts arg
end

7. __FILE__ and __LINE__

__FILE__ represents the name of the current source file, while __LINE__ returns the current line number.

puts "This code is in file: #{__FILE__}, line: #{__LINE__}"