How can I tell what version of Ruby/Rails an app was written for by examining the code?

I've gotten a Rails app from someone via heroku to modify. How can I tell, by examining the source code, what version of Rails was used to writ开发者_开发百科e the app?

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For Rails 3.x

It should be specified in the GEM file

For Rails 2.x - try the config/environment.rb

The file config/environment.rb may specify it e.g.

\# Specifies gem version of Rails to use when vendor/rails is not present
RAILS_GEM_VERSION = '2.3.11' unless defined? RAILS_GEM_VERSION

... but it is not required to.

You can take some educated guesses and try 2.3.2 or 2.3.11. Our own system uses a ton of gems and was pretty happy with 2.3.2 for at least a year.

Which Ruby Version?

A reasonable guess would be 1.8.7 as it has been around for so long. You could also try 1.9.2 but if the app has been around for more than a year, it is unlikely to be using 1.9.x - too many popular gems had problems with 1.9 until this last year or so.

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As of Rails 3 it will be in the Gemfile:

gem 'rails', '3.1.0.rc4'

Before Rails 3 it was in config/environment.rb:

RAILS_GEM_VERSION = '2.3.9' unless defined? RAILS_GEM_VERSION

As for the ruby version, there's no way to tell from code. Most rails code will run fine on either Ruby 1.8 or 1.9.

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It's listed in the Gemfile file.

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To find out the version of ruby there is a possibility that you can go into the .rvm/log file to see the versions that have been used and the dates they were installed.