Building Command-Line Interface Applications with Ruby — A Quick Start Guide

2 min readMar 26, 2023

Introduction

Command-Line Interface (CLI) applications are a convenient and efficient way to perform various tasks and automate processes without relying on graphical user interfaces. Ruby, a versatile and expressive programming language, is an excellent choice for building CLI applications. In this article, we’ll explore how to create a simple CLI application using Ruby and introduce you to some helpful gems that can enhance your application’s functionality.

Setting up the environment

First, ensure that you have Ruby installed on your system. You can check your Ruby version by running the following command in your terminal:

$ ruby -v

If you don’t have Ruby installed, follow the installation instructions on the official Ruby website (https://www.ruby-lang.org/en/documentation/installation/).

Creating a basic CLI application

To begin, create a new file called my_cli_app.rb and open it in your favorite text editor. Add the following code:

#!/usr/bin/env ruby

def main
  puts 'Hello, CLI!'
end

main if __FILE__ == $PROGRAM_NAME

This simple CLI application prints “Hello, CLI!” when executed. The #!/usr/bin/env ruby line tells your system to use the Ruby interpreter to run the script. The main if __FILE__ == $PROGRAM_NAME line ensures that the main method is only called when the script is executed directly, allowing the script to be used as a library if needed.

Save the file and make it executable by running:

$ chmod +x my_cli_app.rb

Now you can run your application:

$ ./my_cli_app.rb
Hello, CLI!

Adding command-line arguments

To make your CLI application more useful, you can accept command-line arguments using the ARGV array. Update your my_cli_app.rb file with the following code:

#!/usr/bin/env ruby

def main
  if ARGV.empty?
    puts 'Usage: ./my_cli_app.rb <your_name>'
    exit
  end

  name = ARGV[0]
  puts "Hello, #{name}!"
end

main if __FILE__ == $PROGRAM_NAME

Now your application will accept a name as an argument:

$ ./my_cli_app.rb Alice
Hello, Alice!

Using gems to enhance your CLI application

Ruby gems can greatly enhance your CLI application. For instance, the thor gem (https://github.com/erikhuda/thor) provides a powerful framework for creating command-line applications with subcommands, options, and arguments.

First, install the thor gem:

$ gem install thor

Then, create a new file called my_thor_cli_app.rb and add the following code:

#!/usr/bin/env ruby

require 'thor'

class MyCLIApp < Thor
  desc 'hello NAME', 'Greets the user with the provided NAME'
  def hello(name)
    puts "Hello, #{name}!"
  end
end

MyCLIApp.start(ARGV)

This example demonstrates a simple thor application with a single hello command. Run the application with:

$ ./my_thor_cli_app.rb hello Alice
Hello, Alice!

Conclusion

We’ve covered the basics of building CLI applications with Ruby. We’ve seen how to create a simple script, accept command-line arguments, and use the thor gem to add more advanced features. With this knowledge, you can start building powerful CLI applications tailored to your specific needs. Good luck, and happy coding!