bundle-update(1) -- Update your gems to the latest available versions
=====================================================================

## SYNOPSIS

`bundle update` <*gems> [--source=NAME]

## DESCRIPTION

Update the gems specified (all gems, if none are specified), ignoring
the previously installed gems specified in the `Gemfile.lock`. In
general, you should use [bundle install(1)][bundle-install] to install the same exact
gems and versions across machines.

You would use `bundle update` to explicitly update the version of a
gem.

## OPTIONS

* `--source=<name>`:
  The name of a `:git` or `:path` source used in the Gemfile(5). For
  instance, with a `:git` source of `http://github.com/rails/rails.git`,
  you would call `bundle update --source rails`

## UPDATING ALL GEMS

If you run `bundle update` with no parameters, bundler will ignore
any previously installed gems and resolve all dependencies again
based on the latest versions of all gems available in the sources.

Consider the following Gemfile(5):

    source "http://rubygems.org"

    gem "rails", "3.0.0.rc"
    gem "nokogiri"

When you run [bundle install(1)][bundle-install] the first time, bundler will resolve
all of the dependencies, all the way down, and install what you need:

    Fetching source index for http://rubygems.org/
    Installing rake (0.8.7)
    Installing abstract (1.0.0)
    Installing activesupport (3.0.0.rc)
    Installing builder (2.1.2)
    Installing i18n (0.4.1)
    Installing activemodel (3.0.0.rc)
    Installing erubis (2.6.6)
    Installing rack (1.2.1)
    Installing rack-mount (0.6.9)
    Installing rack-test (0.5.4)
    Installing tzinfo (0.3.22)
    Installing actionpack (3.0.0.rc)
    Installing mime-types (1.16)
    Installing polyglot (0.3.1)
    Installing treetop (1.4.8)
    Installing mail (2.2.5)
    Installing actionmailer (3.0.0.rc)
    Installing arel (0.4.0)
    Installing activerecord (3.0.0.rc)
    Installing activeresource (3.0.0.rc)
    Installing bundler (1.0.0.rc.3)
    Installing nokogiri (1.4.3.1) with native extensions
    Installing thor (0.14.0)
    Installing railties (3.0.0.rc)
    Installing rails (3.0.0.rc)

    Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.

As you can see, even though you have just two gems in the Gemfile(5), your application
actually needs 25 different gems in order to run. Bundler remembers the exact versions
it installed in `Gemfile.lock`. The next time you run [bundle install(1)][bundle-install], bundler skips
the dependency resolution and installs the same gems as it installed last time.

After checking in the `Gemfile.lock` into version control and cloning it on another
machine, running [bundle install(1)][bundle-install] will _still_ install the gems that you installed
last time. You don't need to worry that a new release of `erubis` or `mail` changes
the gems you use.

However, from time to time, you might want to update the gems you are using to the
newest versions that still match the gems in your Gemfile(5).

To do this, run `bundle update`, which will ignore the `Gemfile.lock`, and resolve
all the dependencies again. Keep in mind that this process can result in a significantly
different set of the 25 gems, based on the requirements of new gems that the gem
authors released since the last time you ran `bundle update`.

## UPDATING A LIST OF GEMS

Sometimes, you want to update a single gem in the Gemfile(5), and leave the rest of the
gems that you specified locked to the versions in the `Gemfile.lock`.

For instance, in the scenario above, imagine that `nokogiri` releases version `1.4.4`, and
you want to update it _without_ updating Rails and all of its dependencies. To do this,
run `bundle update nokogiri`.

Bundler will update `nokogiri` and any of its dependencies, but leave alone Rails and
its dependencies.

## OVERLAPPING DEPENDENCIES

Sometimes, multiple gems declared in your Gemfile(5) are satisfied by the same
second-level dependency. For instance, consider the case of `thin` and
`rack-perftools-profiler`.

    source "http://rubygems.org"

    gem "thin"
    gem "rack-perftools-profiler"

The `thin` gem depends on `rack >= 1.0`, while `rack-perftools-profiler` depends
on `rack ~> 1.0`. If you run bundle install, you get:

    Fetching source index for http://rubygems.org/
    Installing daemons (1.1.0)
    Installing eventmachine (0.12.10) with native extensions
    Installing open4 (1.0.1)
    Installing perftools.rb (0.4.7) with native extensions
    Installing rack (1.2.1)
    Installing rack-perftools_profiler (0.0.2)
    Installing thin (1.2.7) with native extensions
    Using bundler (1.0.0.rc.3)

In this case, the two gems have their own set of dependencies, but they share
`rack` in common. If you run `bundle update thin`, bundler will update `daemons`,
`eventmachine` and `rack`, which are dependencies of `thin`, but not `open4` or
`perftools.rb`, which are dependencies of `rack-perftools_profiler`. Note that
`bundle update thin` will update `rack` even though it's _also_ a dependency of
`rack-perftools_profiler`.

`In short`, when you update a gem using `bundle update`, bundler will update all
dependencies of that gem, including those that are also dependencies of another gem.

In this scenario, updating the `thin` version manually in the Gemfile(5),
and then running [bundle install(1)][bundle-install] will only update `daemons` and `eventmachine`,
but not `rack`. For more information, see the `CONSERVATIVE UPDATING` section
of [bundle install(1)][bundle-install].

## RECOMMENDED WORKFLOW

In general, when working with an application managed with bundler, you should
use the following workflow:

* After you create your Gemfile(5) for the first time, run

    $ bundle install

* Check the resulting `Gemfile.lock` into version control

    $ git add Gemfile.lock

* When checking out this repository on another development machine, run

    $ bundle install

* When checking out this repository on a deployment machine, run

    $ bundle install --deployment

* After changing the Gemfile(5) to reflect a new or update dependency, run

    $ bundle install

* Make sure to check the updated `Gemfile.lock` into version control

    $ git add Gemfile.lock

* If [bundle install(1)][bundle-install] reports a conflict, manually update the specific
  gems that you changed in the Gemfile(5)

    $ bundle update rails thin

* If you want to update all the gems to the latest possible versions that
  still match the gems listed in the Gemfile(5), run

    $ bundle update