How to Use bundle exec in Ruby: Simple Guide

Use bundle exec before a Ruby command to run it with the gems specified in your Gemfile.lock. This ensures your script uses the exact gem versions your project depends on, avoiding conflicts.

Syntax

The basic syntax of bundle exec is:

• bundle exec <command> [arguments]

Here, bundle exec runs the given command using the gems listed in your project's Gemfile.lock. Any arguments are passed to the command.

bash

bundle exec ruby my_script.rb

Example

This example shows how to run a Ruby script using bundle exec to ensure it uses the correct gem versions.

ruby

# Gemfile
source 'https://rubygems.org'
gem 'colorize', '~> 0.8.1'

# my_script.rb
require 'colorize'
puts 'Hello, world!'.colorize(:green)

Output

Hello, world! (in green text color)

Common Pitfalls

Common mistakes when using bundle exec include:

• Not running bundle install first, so gems are missing.
• Running commands without bundle exec, causing the system to use wrong gem versions.
• Using bundle exec with commands not installed by Bundler.

Always run bundle install before using bundle exec and confirm your command is part of your bundle.

bash

Wrong way:
ruby my_script.rb

Right way:
bundle exec ruby my_script.rb

Quick Reference

Command	Description
bundle exec ruby my_script.rb	Run Ruby script with gems from Gemfile.lock
bundle exec rake db:migrate	Run rake task using bundled gems
bundle exec rspec	Run tests with correct gem versions

Key Takeaways

Use bundle exec to run commands with the exact gems your project needs.

Always run bundle install before using bundle exec to install gems.

Without bundle exec, your system might use wrong or global gem versions.

Use bundle exec with commands installed via your Gemfile for consistent results.