Command Line Arguments in Ruby language

As the name says itself Command line arguments, you can assume pretty correct that these might be the arguments you pass while running your Ruby programs as how we pass arguments to a method.

$ ruby languages.rb Ruby C Python JavaScript

Where

• ruby languages.rb is the way to run Ruby program
• Ruby, C, Python and JavaScript are four different arguments passed to it

Varying the number of arguments (ARGV Array)

ARGV stands for ARGument Vector which is a one-dimensional Array. It contains the full list of arguments in the order as passed as arguments.

Key points to remember

• ARGV is an array which contains all the argument passed while running Ruby program.
• You can use ARGV.length method to find the total arguments passed.
• You can use ARGV.each method to iterate over the list of arguments and then perform operation on each argument.
• You can use __FILE__ pseudo variable to access the file name from Ruby program. See Ruby Pseudo Variables.

Example

Create a file named languages.rb and type following lines.

puts "File name is: #{__FILE__}"
puts "Total arguments length: #{ARGV.length}"
puts "Arguments are:"

ARGV.each do |arg|
  puts arg
end

And, run languages.rb as

$ ruby cmd.rb Ruby C Python JavaScript

# output:
File name is: languages.rb
Total arguments length: 4
Arguments are:
Ruby
C
Python
JavaScript

Exercises

• Write a command line program to check whether given number is even or odd.

  Create file named cmd_even_odd.rb.

  num = ARGV[0]       # store into meaningful variable
  num = num.to_i      # convert the numeric string into integer
  puts "Checking whether number #{num} is even or odd"
  
  if num.even?
    puts "#{num} is even."
  else
    puts "#{num} is odd."
  end
  

  Run the program as:

  $ ruby cmd_even_odd.rb 10
  
  # output:
  Checking whether number 10 is even or odd
  10 is even.
  
  $ ruby cmd_even_odd.rb 5
  # output:
  Checking whether number 5 is even or odd
  5 is odd.
  

• Write a command line program to display your name, phone and age. If age is above 16 then print message as “You are an adult now.

  Create file named info.rb.

  name, phone, age = ARGV[0], ARGV[1], ARGV[2]
  age = age.to_i
  puts "Name is #{name}"
  puts "Phone is #{phone}"
  
  if age > 16
    puts "You are an adult now."
  else
    puts "You are yet to become adult."
  end
  

  Run the program as:

  $ ruby info.rb Foo 1213131 17
  
  # output:
  Name is Foo
  Phone is 1213131
  You are an adult now.