## Using Bundler while developing a gem

If you're creating a gem from scratch, you can use bundler's built in gem skeleton to create a base gem for you to edit.

~~~
$ bundle gem my_gem
~~~

This will create a new directory named `my_gem` with your new gem skeleton.
If you already have a gem, you can create a Gemfile and use Bundler to manage your development dependencies. Here's an example.

~~~ruby
source "https://rubygems.org"
gemspec
gem "rspec", "~> 3.9"
gem "rubocop", "0.79.0"
~~~

In this Gemfile, the `gemspec` method imports gems listed with `add_runtime_dependency` in the `my_gem.gemspec` file, and it also installs rspec and rubocop to test and develop the gem.
All dependencies from the gemspec and Gemfile will be installed by `bundle install`, but rspec and rubocop will not be included by `gem install mygem` or `bundle add mygem`.
Declaring development dependencies in the Gemfile like this, rather than with `add_development_dependency` in the gemspec, is the recommended layout. See [Gemfile and gemspec](/gemfile-and-gemspec) for the reasoning.
Runtime dependencies in your gemspec are treated as if they are listed in your Gemfile, and development dependencies are added by default to the group, `:development`.
You can change that group with the `:development_group` option:

~~~ruby
gemspec :development_group => :dev
~~~

You can also point to a specific gemspec directory using the `:path` option. If your gemspec is in `/gemspec/path`, use:

~~~ruby
gemspec :path => '/gemspec/path'
~~~

If you omit `:path`, Bundler will look for gemspecs in the same directory as the Gemfile (usually the project root).

If you have multiple gemspecs in the same directory, specify which one you'd like to reference using `:name`. This refers to the gem name **declared inside the gemspec**, not the gemspec filename:

~~~ruby
gemspec :name => 'my_awesome_gem'
~~~

This will match the gemspec where `spec.name = "my_awesome_gem"`, regardless of whether it's defined in `my_awesome_gem.gemspec` or another file.

That's it! Use bundler when developing your gem, and otherwise, use gemspecs normally!

~~~
$ gem build my_gem.gemspec
~~~