bundler vs RVM vs gems vs RubyGems vs gemsets vs system ruby
I am new to Ruby and trying to wrap my head around following concepts: bundler vs RVM vs gems vs RubyGems vs gemsets vs system rub and I'm confused.
Can someone please describe a 'best practice' of how I should manage all this on a fresh install of the latest version of Ubuntu? What should I install, and how should I use it all?
I'm guessing that doing a sudo apt-get install ruby is not be recommended, but I am not sure. I tried it on my system in addition to 'all the other Ruby stuff'. It's just adding to my confusion. I am not talking about Rails but just regular Ruby gems (e.g. Vagrant, Chef, scripts).
Answer
As per the previous answer, this is quite a lot to cover, so consider this a short introduction.
gems are the way Ruby libraries are packaged. They are to Ruby what jars are to Java. Inside a gem file, you find Ruby code (.rb files), but also tests, and a special file giving information on the gem itself, such as its name, dependencies and version (gemspec). Any Ruby project can define the gems it needs via a Gemfile that just need to declare dependencies. Rubygems is the name of the package manager - the tool used to install the packages (while the gems are the packages themselves). Rubygems is now part of Ruby.
Bundler is what makes managing gems bearable. Based on your Gemfile, a simple call to bundler using bundle install will download and install all the required gems. Using standard gem command, you would have to install each of them manually, using gem install <gem_name>. Bundler is not part of Ruby (it is itself packaged as a gem), but it a "de facto standard" for most applications (you will not find many people not using it, and no good reasons not to use it, actually).
RVM is a tool allowing you to install multiple versions of Ruby on a machine, switching between them when needed. This can be used to install both a Ruby 1.8 and 1.9, or even a "MRI" (Matz's Ruby, the default implementation) and alternatives (such as JRuby or Rubinius). Note that RVM is not alone in this field, see for instance rbenv.
A gemset in RVM is a set of gems specific to a given context, typically a project. This is useful if you are for example developing different applications, each with its own sets of gems, and want to keep them separate.
system Ruby is, when using RVM, the Ruby version installed on the machine (ie, not via RVM).
If you are just starting, gems and bundler are of interest to you. You can let RVM and gemsets aside for now.