## Bundler 0.9 to 1.0 and above

Upgrading from Bundler 0.9 to 1.0 is relatively painless. The
Gemfile API is the same, so your old Gemfiles should continue
to work.

The "env" file that 0.9 created at `.bundle/environment.rb` has been
removed. As a side effect of this, Passenger will only find your
bundled gems if you install with `bundle install --deployment`.
Alternatively, you can tell Passenger where you gems are installed,
[something like this](http://andre.arko.net/2010/08/16/using-passengerpane-with-gem_home-set/).

The `bundle lock` command is no longer needed, as the
Gemfile.lock file is now automatically generated by `bundle install`.
If you have not yet done so, add your Gemfile.lock to source control
and check it in.

Running `bundle install` no longer updates the versions of your gems.
If you need to update just one gem, run `bundle update GEMNAME`. To
update all gems to the newest versions possible, run `bundle update`.

Bundler now supports multiple platforms, using a block syntax to
declare platform-specific gems:

    platform :jruby do
      gem "jruby-maven-plugins"
    end

Deploying using Bundler is even easier than it was before, as Bundler
now includes a Capistrano recipe. Simply add this line to the top of
your deploy.rb file to run Bundler automatically as part of deploying:

    require 'bundler/capistrano'

For more details on deploying using bundler, see the documentation
for the bundler cap task, and the [documentation on deploying](http://bundler.io/deploying.html).


## Bundler 0.8 to 0.9 and above

Upgrading to Bundler 0.9 from Bundler 0.8 requires upgrading several
API calls in your Gemfile, and some workarounds if you are using Rails 2.3.

### Gemfile Removals

Bundler 0.9 removes the following Bundler 0.8 Gemfile APIs:

1. `disable_system_gems`: This is now the default (and only) option
   for bundler. Bundler uses the system gems you have specified
   in the Gemfile, and only the system gems you have specified
   (and their dependencies)
2. `disable_rubygems`: This is no longer supported. We are looking
   into ways to get the fastest performance out of each supported
   scenario, and we will make speed the default where possible.
3. `clear_sources`: Bundler now defaults to an empty source
   list. If you want to include Rubygems, you can add the source
   via source "http://gemcutter.org". If you use bundle init, this
   source will be automatically added for you in the generated
   Gemfile
4. `bundle_path`: You can specify this setting when installing
   via `bundle install /path/to/bundle`. Bundler will remember
   where you installed the dependencies to on a particular
   machine for future installs, loads, setups, etc.
5. `bin_path`: Bundler no longer generates executables in the root
   of your app. You should use `bundle exec` to execute executables
   in the current context.

### Gemfile Changes

Bundler 0.9 changes the following Bundler 0.8 Gemfile APIs:

1. Bundler 0.8 supported :only and :except as APIs for describing
   groups of gems. Bundler 0.9 supports a single `group` method,
   which you can use to group gems together. See the above "Group"
   section for more information.

   This means that `gem "foo", :only => :production` becomes
   `gem "foo", :group => :production`, and
   `only :production { gem "foo" }` becomes
   `group :production { gem "foo" }`

   The short version is: group your gems together logically, and
   use the available commands to make use of the groups you've
   created.

2. `:require_as` becomes `:require`

3. `:vendored_at` is fully removed; you should use `:path`

### API Changes

1. `Bundler.require_env(:environment)` becomes
   `Bundler.require(:multiple, :groups)`. You must
   now specify the default group (the default group is the
   group made up of the gems not assigned to any group)
   explicitly. So `Bundler.require_env(:test)` becomes
   `Bundler.require(:default, :test)`

2. `require 'vendor/gems/environment'`: In unlocked
   mode, where using system gems, this becomes
   `Bundler.setup(:multiple, :groups)`. If you don't
   specify any groups, this puts all groups on the load
   path. In locked mode, it becomes `require '.bundle/environment'`