How To Debug Ruby


Debugging is an essential skill for every developer. It’s the process of identifying and resolving problems in your code. No matter how experienced you are or how well you write your programs, you will inevitably encounter bugs in your code. In this blog post, we will discuss some practical techniques and tools to help you debug Ruby code effectively.

1. Use puts or p to Print Variables

Printing variables to the console may be the simplest way to debug your code. Although it might not be the most sophisticated method, it’s often the quickest way to check the value of variables at different points in your code. Use the puts or p method to print variables to the console.

def some_method
  x = 5
  y = 10
  puts "x: #{x}, y: #{y}"
  result = x + y

The p method is similar to puts but provides a more detailed output by calling the .inspect method on the object. This can be helpful when debugging objects with more complex structures.

2. Use ruby -r debug to Start the Debugger

The built-in debugger is a powerful tool that allows you to step through your code one line at a time, inspect variables, and execute arbitrary Ruby expressions. To start the debugger, run your Ruby script with the -r debug flag.

$ ruby -r debug my_script.rb

This will start your script and pause its execution at the first line. At any point, you can use various debugger commands to control the program’s execution, such as n (next), s (step), c (continue), and q (quit). To inspect the value of a variable, just enter the variable name in the debugger and press Enter.

3. Use the pry Gem for Advanced Debugging

Pry is a powerful alternative to the built-in debugger that offers advanced features such as syntax highlighting, command history, and a more user-friendly interface. To use Pry, first install the gem:

$ gem install pry

Next, add the following line to your code where you want to set a breakpoint:

require 'pry'; binding.pry

When your program reaches this line, Pry will pause its execution and allow you to interactively debug your code.

4. Use rubocop to Catch Syntax Errors and Inconsistencies

Rubocop is a static code analyzer and formatter that can help you find syntax errors, potential bugs, and inconsistencies in your code. It enforces the Ruby community’s coding style and best practices, making your code easier to read and maintain.

To get started, install the Rubocop gem:

$ gem install rubocop

Then run Rubocop on your Ruby files or directories to scan your code for issues:

$ rubocop my_script.rb

5. Write Tests to Validate Your Code

Writing tests is an essential practice to ensure your code works as expected and to catch bugs before they become a problem. Ruby has several testing frameworks that you can use, such as MiniTest (included in Ruby’s standard library) and RSpec.

By writing tests for your code, you can catch errors early and ensure your code behaves as expected. Plus, having a good test suite makes it easier to debug and refactor your code with confidence.


Debugging is a fundamental skill for every Ruby developer. By using the techniques and tools mentioned in this blog post, you can quickly identify and fix issues in your code, making your programs more reliable and efficient. Happy debugging!

© 2021 Debugging Ruby – All Rights Reserved.