Specifying rails version to use when creating a new application - ruby-on-rails

Question

I have two versions of rails (2.1.0 and 2.2.2) installed in my computer.
When I create a new application, is it possible to specify that I want to use the older (2.1.0) version?

Answer 1

I found here an undocumented option to create a new application using an older version of Rails.
rails _2.1.0_ new myapp

Answer 2

Here is the command which I use normally:
rails _version_ new application_name
for example rails _7.0.4_ new my_app
Here is the list of all available rails versions so far:
http://rubygems.org/gems/rails/versions

Answer 3

I was having some trouble using rails _version_ new application_name (the resulting project was still generated for the newest version of Rails installed.)
After a bit of digging I found an article by Michael Trojanek with an alternative approach. This works by creating a folder with a Gemfile specifying the desired version of Rails and then using bundle exec rails... so that Bundler takes care of running the appropriate version of rails. e.g. to make a new Rails 4.2.9 projects the steps are:
mkdir myapp
cd myapp
echo "source 'https://rubygems.org'" > Gemfile
echo "gem 'rails', '4.2.9'" >> Gemfile
bundle install
bundle exec rails new . --force --skip-bundle
bundle update

Answer 4

As rightly pointed out by #mikej for Rails 5.0.0 or above, you should be following these steps:
Create a directory for your application along with a Gemfile to specify your desired Rails version and let bundler install the dependent gems:
$ mkdir myapp
$ cd myapp
$ echo "source 'https://rubygems.org'" > Gemfile
$ echo "gem 'rails', '5.0.0.1'" >> Gemfile
$ bundle install
Check that the correct version of rails has been installed: $ bundle exec rails -v
Now create your application, let Rails create a new Gemfile (or rather overwrite the existing one by using the --force flag) and instead of installing the bundle (--skip-bundle) update it manually:
$ bundle exec rails new . --force --skip-bundle
If you check the entry for rails in Gemfile, it should be like this:
gem 'rails', '~> 5.0.0', '>= 5.0.0.1'
You should update it to the exact version needed for the application:
gem 'rails', '5.0.0.1'
Now, the final step:
$ bundle update

Answer 5

There are two ways to achieve this:
one as suggested in accepted answer:
gem install rails -v 2.1.0 #only when the gem has not been installed in the desired ruby version you are using, so that you don't get error on next step
rails _2.1.0_ new my_app
and alternative method is to create gemfile with desired rails version before initializing rails project
mkdir my_app
cd my_app
echo "source 'https://rubygems.org'" > Gemfile
echo "gem 'rails', '2.1.0'" >> Gemfile
bundle install
bundle exec rails new . --force --skip-bundle
I have written about this in details in my article

Answer 6

You can generate the skeleton with either version and require the one you want in config/environment.rb:
# Specifies gem version of Rails to use when vendor/rails is not present
RAILS_GEM_VERSION = '2.1.2' unless defined? RAILS_GEM_VERSION
or use the "rails" command form the version you want anyway.

Answer 7

You should also take a look at "freezing" your Rails gems into the app. This helps a lot with deployment, specially in shared hosting environments.
Just change the RAILS_GEM_VERSION variable in config/environment.rb and issue the freeze rake task:
rake rails:freeze:gems

Answer 8

Please watch out which version of ruby you are using with Rails.
The command for making a new project for a specific version of Rail may not work for you. I had some issues about it. And the problem was the ruby version I have default which is 3.0.0. This version did not work with Rails 5. Then I installed ruby 2.7.5 and switched to it as default. Only then I was able to make projects both for Rails 5 and 7.
If you want the same environment with ruby 2.7.5
rvm install ruby-2.7.5
switch to this version as default
rvm --default use 2.7.5
install bundler and webpacker
gem install bundler
gem install webpacker
install lastest rails (which is 7)
gem install rails
test it
rails new test_app_6
cd test_app_6
rails s
check for localhost 3000
http://localhost:3000
then stop the server (control + c) and install Rails 5
gem install rails -v 5.2.6
test it
rails _5.2.6_ new test_app_5
cd test_app_5
rails s
check for localhost 3000
http://localhost:3000
You're set!