How do I upgrade Rails? - ruby-on-rails

Question

I am new to Ruby and Rails, as well as all this command line melarky. So please bear with me.
I have installed, RubyGems, Homebrew, RVM, Rails etc, by following various tutorials.
I think I have all of this going now, but when I type:
rails --version
I get, 3.2.12. I notice that Rails 4 is out. How do I upgrade to this version?
If I do:
gem install rails
Even doing:
gem update rails
I still get 3.2.12.
Any ideas?
UPDATE
When trying a few options here, I get this message returned...
Michaels-MacBook-Pro:~ ParanoidAndroid$ gem install rails --version=4.0
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/usr/local/rvm/rubies/ruby-1.9.3-p392/bin/ruby extconf.rb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/usr/local/rvm/rubies/ruby-1.9.3-p392/bin/ruby
--with-atomic_reference-dir
--without-atomic_reference-dir
--with-atomic_reference-include
--without-atomic_reference-include=${atomic_reference-dir}/include
--with-atomic_reference-lib
--without-atomic_reference-lib=${atomic_reference-dir}/lib
/usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:461:in `try_link0'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/1.9.1/mkmf.rb:712:in `try_run'
from extconf.rb:26:in `<main>'
Gem files will remain installed in /usr/local/rvm/gems/ruby-1.9.3-p392/gems/atomic-1.1.14 for inspection.
Results logged to /usr/local/rvm/gems/ruby-1.9.3-p392/gems/atomic-1.1.14/ext/gem_make.out
Seems there's an error happening. Any further ideas?
Thanks again everyone!

Answer 1

If you already have a Rails project you should:
Specify the desired version in your Gemfile (e.g. gem 'rails', '~> 5.2.0.rc1')
Run bundle install (bundle update may be needed)
Run rails app:update (rake rails:update for 4.2 and earlier)
Follow instructions on screen
Follow the official guide for additional steps depending on your version

Answer 2

If you are using RVM then you should create a seperate gemset first like:
rvm gemset create whateverName
in this example I will install rails 4
rvm install 2.0.0
rvm list
rvm 2.0.0
^^^^(you may need to copy and paste the version number exactly here as it was displayed in rvm list)
rvm gemset create rails4
rvm gemset use rails4
add the following to your gemfile for existing apps
gem 'rails', '4.0.0'
then run
bundle update rails
or do following to just install the gem
gem install rails --version=4.0
UPDATE
If you havne't installed Xcode 4.5 CLI tools then you will need to
Preferences > Downloads > Components
DMG
https://developer.apple.com/downloads
you may then also need to use homebrew to update gcc
brew install apple-gcc42
the following link has all the information you will need:
https://thoughtbot.com/blog/the-hitchhikers-guide-to-riding-a-mountain-lion

Answer 3

gem update rails does nothing for you, because bundler makes sure that only the gems specified in your Gemfile are loaded and used.
So in order to upgrade to Rails 4, you need to change the Rails version number in your Gemfile and run bundle update rails.
This Railscast guides you through all the steps of manually updating an existing application from Rails 3.2 to Rails 4:
http://railscasts.com/episodes/415-upgrading-to-rails-4

Answer 4

You can install either with specific version OR putting gem version in itself Gemfile.
gem install rails -v 4.0.0

Answer 5

You can get a list of all gem versions with
gem list rails --remote --all
To install specify version 4.0.1 for example you can use
gem install rails -v 4.0.1
Or you could just specify the version in your Gemfile

Answer 6

Best to use gem list --remote --all. Unless your looking for that particular version as long as the gemset for that project has been established