bundle-exec(1) -- Execute a command in the context of the bundle
================================================================

## SYNOPSIS

`bundle exec` [--keep-file-descriptors] <command>

## DESCRIPTION

This command executes the command, making all gems specified in the
`Gemfile(5)` available to `require` in Ruby programs.

Essentially, if you would normally have run something like
`rspec spec/my_spec.rb`, and you want to use the gems specified
in the `Gemfile(5)` and installed via [bundle install(1)][bundle-install], you
should run `bundle exec rspec spec/my_spec.rb`.

Note that `bundle exec` does not require that an executable is
available on your shell's `$PATH`.

## OPTIONS

* `--keep-file-descriptors`:
  Exec in Ruby 2.0 began discarding non-standard file descriptors. When this
  flag is passed, exec will revert to the 1.9 behaviour of passing all file
  descriptors to the new process.

## BUNDLE INSTALL --BINSTUBS

If you use the `--binstubs` flag in [bundle install(1)][bundle-install], Bundler will
automatically create a directory (which defaults to `app_root/bin`)
containing all of the executables available from gems in the bundle.

After using `--binstubs`, `bin/rspec spec/my_spec.rb` is identical
to `bundle exec rspec spec/my_spec.rb`.

## ENVIRONMENT MODIFICATIONS

`bundle exec` makes a number of changes to the shell environment,
then executes the command you specify in full.

* make sure that it's still possible to shell out to `bundle`
  from inside a command invoked by `bundle exec` (using
  `$BUNDLE_BIN_PATH`)
* put the directory containing executables (like `rails`, `rspec`,
  `rackup`) for your bundle on `$PATH`
* make sure that if bundler is invoked in the subshell, it uses
  the same `Gemfile` (by setting `BUNDLE_GEMFILE`)
* add `-rbundler/setup` to `$RUBYOPT`, which makes sure that
  Ruby programs invoked in the subshell can see the gems in
  the bundle

It also modifies Rubygems:

* disallow loading additional gems not in the bundle
* modify the `gem` method to be a no-op if a gem matching
  the requirements is in the bundle, and to raise a
  `Gem::LoadError` if it's not
* Define `Gem.refresh` to be a no-op, since the source
  index is always frozen when using bundler, and to
  prevent gems from the system leaking into the environment
* Override `Gem.bin_path` to use the gems in the bundle,
  making system executables work
* Add all gems in the bundle into Gem.loaded_specs

### Loading

By default, when attempting to `bundle exec` to a file with a ruby shebang,
Bundler will `Kernel.load` that file instead of using `Kernel.exec`. For the
vast majority of cases, this is a performance improvement. In a rare few cases,
this could cause some subtle side-effects (such as dependence on the exact
contents of `$0` or `__FILE__`) and the optimization can be disabled by enabling
the `disable_exec_load` setting.

### Shelling out

Any Ruby code that opens a subshell (like `system`, backticks, or `%x{}`) will
automatically use the current Bundler environment. If you need to shell out to
a Ruby command that is not part of your current bundle, use the
`with_clean_env` method with a block. Any subshells created inside the block
will be given the environment present before Bundler was activated. For
example, Homebrew commands run Ruby, but don't work inside a bundle:

    Bundler.with_clean_env do
      `brew install wget`
    end

Using `with_clean_env` is also necessary if you are shelling out to a different
bundle. Any Bundler commands run in a subshell will inherit the current
Gemfile, so commands that need to run in the context of a different bundle also
need to use `with_clean_env`.

    Bundler.with_clean_env do
      Dir.chdir "/other/bundler/project" do
        `bundle exec ./script`
      end
    end

Bundler provides convenience helpers that wrap `system` and `exec`, and they
can be used like this:

    Bundler.clean_system('brew install wget')
    Bundler.clean_exec('brew install wget')


## RUBYGEMS PLUGINS

At present, the Rubygems plugin system requires all files
named `rubygems_plugin.rb` on the load path of _any_ installed
gem when any Ruby code requires `rubygems.rb`. This includes
executables installed into the system, like `rails`, `rackup`,
and `rspec`.

Since Rubygems plugins can contain arbitrary Ruby code, they
commonly end up activating themselves or their dependencies.

For instance, the `gemcutter 0.5` gem depended on `json_pure`.
If you had that version of gemcutter installed (even if
you _also_ had a newer version without this problem), Rubygems
would activate `gemcutter 0.5` and `json_pure <latest>`.

If your Gemfile(5) also contained `json_pure` (or a gem
with a dependency on `json_pure`), the latest version on
your system might conflict with the version in your
Gemfile(5), or the snapshot version in your `Gemfile.lock`.

If this happens, bundler will say:

    You have already activated json_pure 1.4.6 but your Gemfile
    requires json_pure 1.4.3. Consider using bundle exec.

In this situation, you almost certainly want to remove the
underlying gem with the problematic gem plugin. In general,
the authors of these plugins (in this case, the `gemcutter`
gem) have released newer versions that are more careful in
their plugins.

You can find a list of all the gems containing gem plugins
by running

    ruby -rubygems -e "puts Gem.find_files('rubygems_plugin.rb')"

At the very least, you should remove all but the newest
version of each gem plugin, and also remove all gem plugins
that you aren't using (`gem uninstall gem_name`).
