How to set up ruby development environment using rbenv
------------------------------------------------------

```
$ brew install rbenv ruby-build
$ echo 'eval "$(rbenv init -)"' >> ~/dotfiles/.bash_profile
```

```
$ rbenv install --list # Display the list of ruby versions.
:
$ rbenv install 2.2.0  # Installing the version of 2.2.0
:
$ rbenv versions       # Display the list of installed ruby versions.
$ rbenv version        # Display the ruby version on current directory.
```

```
$ rbenv version
system (set by /Users/masashi/.rbenv/version)
$ rbenv global 2.2.0
$ rbenv rehash
$ rbenv version
2.2.0 (set by /Users/masashi/.rbenv/version)
```

```
$ which gem
/Users/masashi/.rbenv/shims/gem
```

```
$ gem install guard
$ gem install guard-shell
$ gem install terminal-notifier-guard
```