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

## SYNOPSIS

`bundle exec` <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`.

## 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

### Shelling out

When shelling out (using the `system` or backticks methods,
for example), Bundler's environment changes will propogate to
the subshell environment. If you desire to shell out without
Bundler's environment changes, simply employ the `with_clean_env`
method. It will restore all environment variables to what they
were before Bundler was activated. For example:

    Bundler.with_clean_env do
      `brew install wget`
    end

## 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`).