Gem bundle install 能在用户的 gem 目录中进行安装吗？
如果用普通用户执行 gem install 会在~/.gem 目录下安装，但是 bundle install 的默认行为是在系统 gem 目录安装，貌似也没有相应的选项啊？ --path 选项好像不对。
bundle package 会把 gem 文件缓存到 vendor/cache 下；
在 gem install vendor/cache/* --local 安装就可以了。
还是会提示输入密码啊，而且这个会把所有依赖的 gem 都下到 cache 下吧，我想要的是把 Gemfile 中没有的 gem 安装到 ome 下面的 gem 目录下。
Make sure all dependencies in your Gemfile are available to your application.
$ bundle install [--system]
Gems will be installed to your default system location for gems. If your system gems are stored in a root-owned location (such as in Mac OSX), bundle will ask for your root password to install them there.
While installing gems, Bundler will check vendor/cache and then your system's gems. If a gem isn't cached or installed, Bundler will try to install it from the sources you have declared in your Gemfile.
The --system option is the default. Pass it to switch back after using the --path option as described below.
Install your dependencies, even gems that are already installed to your system gems, to a location other than your system's gem repository. In this case, install them to vendor/bundle.
$ bundle install --path vendor/bundle