Retrieves or sets a configuration value. If only parameter is provided, retrieve the value. If two parameters are provided, replace the existing value with the newly provided one.

By default, setting a configuration value sets it for all projects on the machine.

If a global setting is superceded by local configuration, this command will show the current value, as well as any superceded values and where they were specified.

You can use bundle config to give bundler the flags to pass to the gem installer every time bundler tries to install a particular gem.

A very common example, the mysql gem, requires Snow Leopard users to pass configuration flags to gem install to specify where to find the mysql_config executable.

$ gem install mysql -- --with-mysql-config=/usr/local/mysql/bin/mysql_config

Since the specific location of that executable can change from machine to machine, you can specify these flags on a per-machine basis.

$ bundle config build.mysql --with-mysql-config=/usr/local/mysql/bin/mysql_config

After running this command, every time bundler needs to install the mysql gem, it will pass along the flags you specified.

Configuration keys in bundler have two forms: the canonical form and the environment variable form.

For instance, passing the --without flag to bundle install prevents Bundler from installing certain groups specified in the Gemfile. Bundler persists this value in app/.bundle/config so that calls to Bundler.setup do not try to find gems from the Gemfile that you didn't install. Additionally, subsequent calls to bundle install remember this setting and skip those groups.

The canonical form of this configuration is "without". To convert the canonical form to the environment variable form, capitalize it, and prepend BUNDLE_. The environment variable form of "without" is BUNDLE_WITHOUT.

The following is a list of all configuration keys and their purpose. You can learn more about their operation in bundle install.

• path (BUNDLE_PATH): The location on disk to install gems. Defaults to $GEM_HOME in development and vendor/bundle when --deployment is used.
• frozen (BUNDLE_FROZEN): Disallow changes to the Gemfile. Defaults to true when --deployment is used.
• without (BUNDLE_WITHOUT): A :-separated list of groups whose gems bundler should not installer
• bin (BUNDLE_BIN): Install executables from gems in the bundle to the specified directory. Defaults to false.
• gemfile (BUNDLE_GEMFILE): The name of the file that bundler should use as the Gemfile. This location of this file also sets the root of the project, which is used to resolve relative paths in the Gemfile, among other things. By default, bundler will search up from the current working directory until it finds a Gemfile.

In general, you should set these settings per-application by using the applicable flag to the bundle install command.

You can set them globally either via environment variables or bundle config, whichever is preferable for your setup. If you use both, environment variables will take preference over global settings.

Bundler also allows you to work against a git repository locally instead of using the remote version. This can be achieved by setting up a local override:

$ bundle config local.GEM_NAME /path/to/local/git/repository

For example, in order to use a local Rack repository, a developer could call:

$ bundle config local.rack ~/Work/git/rack

Now instead of checking out the remote git repository, the local override will be used. Similar to a path source, every time the local git repository change, changes will be automatically picked up by Bundler. This means a commit in the local git repo will update the revision in the Gemfile.lock to the local git repo revision. This requires the same attention as git submodules. Before pushing to the remote, you need to ensure the local override was pushed, otherwise you may point to a commit that only exists in your local machine.

Bundler does many checks to ensure a developer won't work with invalid references. Particularly, we force a developer to specify a branch in the Gemfile in order to use this feature. If the branch specified in the `Gemfile` and the current branch in the local git repository do not match, Bundler will abort. This ensures that a developer is always working against the correct branches, and prevents accidental locking to a different branch.

Finally, Bundler also ensures that the current revision in the Gemfile.lock exists in the local git repository. By doing this, Bundler forces you to fetch the latest changes in the remotes.