Bundler : A gem to bundle gems
Github: http://github.com/wycats/bundler Mailing list: http://groups.google.com/group/ruby-bundler 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.
Bundler has no dependencies. Just clone the git repository and install the gem with the following rake task:
You can also install the gem with
gem install bundler
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.
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 require that gem in the "testing" # environment. :except is also a valid option to specify environment # restrictions. gem "rspec", :only => :testing # Specify a dependency, but specify that it is already present and expanded # at vendor/rspec. Bundler will treat rspec as though it was the rspec gem # for the purpose of gem resolution: if another gem depends on a version # of rspec satisfied by "1.1.6", it will be used. # # If a gemspec is found in the directory, it will be used to specify load # paths and supply additional dependencies. # # Bundler will also recursively search for *.gemspec, and assume that # gemspecs it finds represent gems that are rooted in the same directory # the gemspec is found in. gem "rspec", "1.1.6", :vendored_at => "vendor/rspec" # Works exactly like :vendored_at, but first downloads the repo from # git and handles stashing the files for you. As with :vendored_at, # Bundler will automatically use *.gemspec files in the root or anywhere # in the repository. gem "rails", "3.0.pre", :git => "git://github.com/rails/rails.git" # Add http://gems.github.com as a source that the bundler will use # to find gems listed in the manifest. By default, # http://gems.rubyforge.org is already added to the list. # # This is an optional setting. source "http://gems.github.com" # 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. disable_rubygems
One of the most important things that the bundler does is do a dependency resolution on the full list of gems that you specify, all at once. This differs from the one-at-a-time dependency resolution that Rubygems does, which can result in the following problem:
# On my system: # activesupport 3.0.pre # activesupport 2.3.4 # activemerchant 1.4.2 # rails 2.3.4 # # activemerchant 1.4.2 depends on activesupport >= 2.3.2 gem "activemerchant", "1.4.2" # results in activating activemerchant, as well as # activesupport 3.0.pre, since it is >= 2.3.2 gem "rails", "2.3.4" # results in: # can't activate activesupport (= 2.3.4, runtime) # for ["rails-2.3.4"], already activated # activesupport-3.0.pre for ["activemerchant-1.4.2"]
This is because activemerchant has a broader dependency, which results in the activation of a version of activesupport that does not satisfy a more narrow dependency.
Bundler solves this problem by evaluating all dependencies at once, so it can detect that all gems together require activesupport "2.3.4".
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, resolve 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
When you run
gem bundle, the following steps occur:
- Gemfile is read in
- The gems specified in the Gemfile are resolved against the gems already in your bundle. If the dependencies resolve, skip to step 5.
- If the dependencies in your Gemfile cannot be fully resolved against the gems already in the bundle, the metadata for each source is fetched.
- The gems in the Gemfile are resolved against the full list of available gems in all sources, and the resulting gems are downloaded
- Each gem that has been downloaded but not yet expanded is expanded into the local directory. This expansion process also installs native gems.
As you can see, if you run gem bundle twice in a row, it will do nothing the second time, since the gems obviously resolve against the installed gems, and they are all expanded.
This also means that if you run
gem bundle, and .gitignore the expanded
copies, leaving only the cached
.gem files, you can run
gem bundle again
on the remote system, and it will only expand out the gems (but not
resolve or download
.gem files). This also means that native gems
will be compiled for the target platform without requiring that the
.gem file itself be downloaded from a remote gem server.
Assuming a Rails app with Bundler's standard setup, add something like
this to your top-level
.gitignore to only keep the cache:
Make sure that you explicitly
git add vendor/gems/cache before you commit.
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
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
You can use
gem exec bash to enter a shell that will run all binaries in
the current context.
Yet another way is to manually require the environment file first. This is
[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. disable_system_gems
You can now use rails if you prepend
gem execto every call to
script/*but that isn't fun.
At the top of
config/preinitializer.rb, add the following line:
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 rubygems features.
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.
This is different from the
disable_system_gems option, which uses the rubygems
library, but prevents system gems from being loaded; only gems that are bundled
will be available to your application. This option guarantees that dependencies
of your application will be available to a remote system.
- When a gem points to a git repository, the git repository will be cloned every time Bundler does a gem dependency resolve.
Please report all bugs on the github issue tracker for the project located at: