How to "Activate" a Different Version of a Particular Gem

How do I activate a different version of a particular gem?

If your problem is to run binaries of a certain version, then:

rails --version # => the latest version
rails _2.3.10_ --version # => Rails 2.3.10

This pattern (gem-binary _gem-version_) works for any gem binary.

Hope it helps.

How to switch between different version of gem installed?

You can specify a version in gemfile of your project

gem "rack",  "1.3.5"

Pointed by matt:

To use gem specified in Gemfile:

bundle exec cucumber

How to run a specific version of a ruby gem

I can't reproduce this issue, but I can think of a few reasons why this might happen:

• Bundler artifacts (perhaps in .bundle/) pointing to the old version. Try running in a different directory and see if it still happens
• A bug in RubyGems (try gem update --system)
• During install, it asked if you wanted to replace the brakeman binary and you selected "no"
• If you are using a Ruby version manager, maybe one version is on a different path than another (like a system gem versus one managed by rvm)
• Any number of GEM_PATH, bundler, gem, rvm weirdness that sometimes occurs

In any case, if I were you I'd gem uninstall brakeman, remove all versions, and install fresh. If you are using rvm, start with a fresh gemset or rvm gemset empty the current one.

how to get bundler to use an older bundler gem version?

You can use bundle _version_ install to install gems using a specific version.

Here's an example:

bundle _1.0.21_ install

or

bundle _1.0.21_ -v
# Bundler version 1.0.2

Reference: http://makandracards.com/makandra/9741-run-specific-version-of-bundler

How to `bundle install` when your Gemfile requires an older version of bundler?

First you need to install the appropriate version of bundler:

% gem install bundler -v '~> 1.0.0'
Successfully installed bundler-1.0.22

Then force rubygems to use the version you want (see this post):

% bundle _1.0.22_ install

Bundler - cannot load 2 different versions of the exact same gem?

You cannot have two different versions of the same gem loaded the same program, because they could conflict and override each other's methods. For example, suppose you have a gem which contains the following:

# In gem version 1.0
class AneMaria
  def self.name
    "Ane"
  end
end

######

# In gem version 2.0
class AneMaria
  def self.name
    "Maria"
  end
end

And then in your code, if you call AneMaria.name, what should it return??

One of the reasons tools like bundler were created was to prevent this from happening accidentally -- so no, you cannot specify 2 different versions of a gem to load simultaneously. (Also, I don't think you'll ever want to do that!)

See also this post, which explains things a little more.

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