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Manage your application's gem dependencies with less pain
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Bundler : A gem to bundle gems

Mailing list:
IRC:          #carlhuda on freenode


Bundler is a tool that manages gem dependencies for your ruby application. It takes a gem manifest file and is able to fetch, download, and install the gems and all child dependencies specified in this manifest. It can manage any update to the gem manifest file and update the bundled gems accordingly. It also lets you run any ruby code in context of the bundled gem environment.


This project is under rapid development. It is usable today, but there will be many changes in the near future, including to the Gemfile DSL. We will bump up versions with changes though. We greatly appreciate feedback.


Bundler has no dependencies. Just clone the git repository and install the gem with the following rake task:

rake install


Bundler requires a gem manifest file to be created. This should be a file named Gemfile located in the root directory of your application. After the manifest has been created, in your shell, cd into your application's directory and run gem bundle. This will start the bundling process.

Manifest file

This is where you specify all of your application's dependencies. By default this should be in a file named Gemfile located in your application's root directory. The following is an example of a potential Gemfile. For more information, please refer to Bundler::ManifestBuilder.

# Specify a dependency on rails. When the bundler downloads gems,
# it will download rails as well as all of rails' dependencies (such as
# activerecord, actionpack, etc...)
# At least one dependency must be specified
gem "rails"

# Specify a dependency on rack v.1.0.0. The version is optional. If present,
# it can be specified the same way as with rubygems' #gem method.
gem "rack", "1.0.0"

# Specify a dependency rspec, but only activate that gem in the "testing"
# environment (read more about environments later). :except is also a valid
# option to specify environment restrictions.
gem "rspec", :only => :testing

# Add as a source that the bundler will use
# to find gems listed in the manifest. By default,
# is already added to the list.
# This is an optional setting.
source ""

# Specify where the bundled gems should be stashed. This directory will
# be a gem repository where all gems are downloaded to and installed to.
# This is an optional setting.
# The default is: vendor/gems
bundle_path "my/bundled/gems"

# Specify where gem executables should be copied to.
# This is an optional setting.
# The default is: bin
bin_path "my/executables"

# Specify that rubygems should be completely disabled. This means that it
# will be impossible to require it and that available gems will be
# limited exclusively to gems that have been bundled.
# The default is to automatically require rubygems. There is also a
# `disable_system_gems` option that will limit available rubygems to
# the ones that have been bundled.

Running Bundler

Once a manifest file has been created, the only thing that needs to be done is to run the gem bundle command anywhere in your application. The script will load the manifest file, resole all the dependencies, download all needed gems, and install them into the specified directory.

Every time an update is made to the manifest file, run gem bundle again to get the changes installed. This will only check the remote sources if your currently installed gems do not satisfy the Gemfile. If you want to force checking for updates on the remote sources, use the --update option.

Running your application

The easiest way to run your application is to start it with an executable copied to the specified bin directory (by default, simply bin). For example, if the application in question is a rack app, start it with bin/rackup. This will automatically set the gem environment correctly.

Another way to run arbitrary ruby code in context of the bundled gems is to run it with the gem exec command. For example:

gem exec ruby my_ruby_script.rb

Yet another way is to manually require the environment file first. This is located in [bundle_path]/environments/default.rb. For example:

ruby -r vendor/gems/environment.rb my_ruby_script.rb

Using Bundler with Rails today

It should be possible to use Bundler with Rails today. Here are the steps to follow.

  • In your rails app, create a Gemfile and specify the gems that your application depends on. Make sure to specify rails as well:

      gem "rails", "2.1.2"
      gem "will_paginate"
      # Optionally, you can disable system gems all together and only
      # use bundled gems.
  • Run gem bundle

  • You can now use rails if you prepend gem exec to every call to script/* but that isn't fun.

  • At the top of config/boot.rb, add the following line:

    require File.expand_path(File.join(File.dirname(__FILE__), '..', 'vendor', 'gems', 'environment'))

In theory, this should be enough to get going.

To require rubygems or not

Ideally, no gem would assume the presence of rubygems at runtime. Rubygems provides enough features so that this isn't necessary. However, there are a number of gems that require specific rubygem features.

If the disable_rubygems option is used, Bundler will stub out the most common of these features, but it is possible that things will not go as intended quite yet. So, if you are brave, try your code without rubygems at runtime.

Known Issues

  • When a gem points to a git repository, the git repository will be cloned every time Bundler does a gem dependency resolve.

Reporting bugs

Please report all bugs on the github issue tracker for the project located at:
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