How to Get a List of Gems That Are Installed That Have Native Extensions

How do I get a list of gems that are installed that have native extensions?

A good start would be to look at the gem specification for each gem and see if it has the extensions field set. That should leave you with a short-list of gems to re-install. They don't necessarily all use native extensions, but if you look at the corresponding extconf.rb files, this should be pretty easy to find out.

Update: Here is a short ruby script to list those gems:

require 'rubygems'

Gem.source_index.each do |gem|
  spec =  Gem.source_index.specification(gem[0])
  ext = spec.extensions
  puts "#{gem[0]} has extensions: #{ext}" unless ext.empty?
end

List of installed gems?

The Gem command is included with Ruby 1.9+ now, and is a standard addition to Ruby pre-1.9.

require 'rubygems'

name = /^/i
dep = Gem::Dependency.new(name, Gem::Requirement.default)
specs = Gem.source_index.search(dep)
puts specs[0..5].map{ |s| "#{s.name} #{s.version}" }
# >> Platform 0.4.0
# >> abstract 1.0.0
# >> actionmailer 3.0.5
# >> actionpack 3.0.5
# >> activemodel 3.0.5
# >> activerecord 3.0.5

---

Here's an updated way to get a list:

require 'rubygems'

def local_gems
   Gem::Specification.sort_by{ |g| [g.name.downcase, g.version] }.group_by{ |g| g.name }
end

Because local_gems relies on group_by, it returns a hash of the gems, where the key is the gem's name, and the value is an array of the gem specifications. The value is an array of the instances of that gem that is installed, sorted by the version number.

That makes it possible to do things like:

my_local_gems = local_gems()

my_local_gems['actionmailer']
# => [Gem::Specification.new do |s|
#       s.authors = ["David Heinemeier Hansson"]
#       s.date = Time.utc(2013, 12, 3)
#       s.dependencies = [Gem::Dependency.new("actionpack",
#         Gem::Requirement.new(["= 4.0.2"]),
#         :runtime),
#        Gem::Dependency.new("mail",
#         Gem::Requirement.new(["~> 2.5.4"]),
#         :runtime)]
#       s.description = "Email on Rails. Compose, deliver, receive, and test emails using the familiar controller/view pattern. First-class support for multipart email and attachments."
#       s.email = "david@loudthinking.com"
#       s.homepage = "http://www.rubyonrails.org"
#       s.licenses = ["MIT"]
#       s.name = "actionmailer"
#       s.require_paths = ["lib"]
#       s.required_ruby_version = Gem::Requirement.new([">= 1.9.3"])
#       s.requirements = ["none"]
#       s.rubygems_version = "2.0.14"
#       s.specification_version = 4
#       s.summary = "Email composition, delivery, and receiving framework (part of Rails)."
#       s.version = Gem::Version.new("4.0.2")
#       end]

And:

puts my_local_gems.map{ |name, specs| 
  [ 
    name,
    specs.map{ |spec| spec.version.to_s }.join(',')
  ].join(' ') 
}
# >> actionmailer 4.0.2
...
# >> arel 4.0.1,5.0.0
...
# >> ZenTest 4.9.5
# >> zucker 13.1

The last example is similar to the gem query --local command-line, only you have access to all the information for a particular gem's specification.

Find out which gems require native c extensions from a Gemfile?

You can use JRuby Lint for that. It will will check for some gems requiring C extension and even list alternative (based on this list).

How to find where gem files are installed

Use gem environment to find out about your gem environment:

RubyGems Environment:
  - RUBYGEMS VERSION: 2.1.5
  - RUBY VERSION: 2.0.0 (2013-06-27 patchlevel 247) [x86_64-darwin12.4.0]
  - INSTALLATION DIRECTORY: /Users/ttm/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0
  - RUBY EXECUTABLE: /Users/ttm/.rbenv/versions/2.0.0-p247/bin/ruby
  - EXECUTABLE DIRECTORY: /Users/ttm/.rbenv/versions/2.0.0-p247/bin
  - SPEC CACHE DIRECTORY: /Users/ttm/.gem/specs
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-12
  - GEM PATHS:
     - /Users/ttm/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0
     - /Users/ttm/.gem/ruby/2.0.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - /Users/ttm/.rbenv/versions/2.0.0-p247/bin
     - /Users/ttm/.rbenv/libexec
     - /Users/ttm/.rbenv/plugins/ruby-build/bin
     - /Users/ttm/perl5/perlbrew/bin
     - /Users/ttm/perl5/perlbrew/perls/perl-5.18.1/bin
     - /Users/ttm/.pyenv/shims
     - /Users/ttm/.pyenv/bin
     - /Users/ttm/.rbenv/shims
     - /Users/ttm/.rbenv/bin
     - /Users/ttm/bin
     - /usr/local/mysql-5.6.12-osx10.7-x86_64/bin
     - /Users/ttm/libsmi/bin
     - /usr/local/bin
     - /usr/bin
     - /bin
     - /usr/sbin
     - /sbin
     - /usr/local/bin

Notice the two sections for:

• INSTALLATION DIRECTORY
• GEM PATHS

How do you precompile the native extensions for a ruby gem for linux?

Finally found a way to do this for gems that use rake-compiler for building their C extensions (which is most of them).

You need to do the following on a machine that is identical to the one you want to deploy to, or it simply won't work:

Install the build prerequisites for building C extensions:

# apt-get install build-essentials ruby-dev # ... etc
# gem install rake-compiler

Unpack the gem you want to rebuild:

$ gem unpack nokogiri

Build your shiny new precompiled gem:

$ rake native gem

You can now install the native gem on a machine without any build tools installed:

$ gem install pkg/nokogiri-1.4.3.1-x86-linux.gem 
Successfully installed nokogiri-1.4.3.1-x86-linux
1 gem installed

ruby install rails with Error ---Failed to build gem native extension.（Windows platform）

Just back from a vacation, and this problem has been solved during the holiday. Forgive me for not remembering to close this issue until now.XD

With the help of Josien's comments, the problem has narrowed down to gem install websocket-driver failed. It's easier to find this problem on stackoverflow-Error when trying to install gem websocket-driver-0.7.3

Finally, I solved this problem just by typing ridk install (to make MSYS2 work for ruby3.0.1)——I have installed MSYS2 and make it work under ruby2.7.4, but if you want to make it work for ruby3.0.1 samely , you need to excute this command under ruby3.0.1.

After installed MSYS2 for ruby3.0.1, rails installed sucessfully.

C:\Users\Administrator>Uru ls
    274p191     : ruby 2.7.4p191 (2021-07-07 revision a21a3b7d23) [x64-mingw32]
    310p0       : ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x64-mingw-ucrt]

C:\Users\Administrator>ruby -v
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x64-mingw-ucrt]

C:\Users\Administrator>ridk install
 _____       _           _____           _        _ _         ___
|  __ \     | |         |_   _|         | |      | | |       |__ \
| |__) |   _| |__  _   _  | |  _ __  ___| |_ __ _| | | ___ _ __ ) |
|  _  / | | | '_ \| | | | | | | '_ \/ __| __/ _` | | |/ _ \ '__/ /
| | \ \ |_| | |_) | |_| |_| |_| | | \__ \ || (_| | | |  __/ | / /_
|_|  \_\__,_|_.__/ \__, |_____|_| |_|___/\__\__,_|_|_|\___|_||____|
                    __/ |           _
                   |___/          _|_ _  __   | | o __  _| _     _
                                   | (_) |    |^| | | |(_|(_)\^/_>

   1 - MSYS2 base installation
   2 - MSYS2 system update (optional)
   3 - MSYS2 and MINGW development toolchain

Which components shall be installed? If unsure press ENTER [1,3] 1,3

> sh -lc true
MSYS2 seems to be properly installed
Install MSYS2 and MINGW development toolchain ...
> pacman -S --needed --noconfirm autoconf autogen automake-wrapper diffutils file 
...
...
...
Install MSYS2 and MINGW development toolchain succeeded

   1 - MSYS2 base installation
   2 - MSYS2 system update (optional)
   3 - MSYS2 and MINGW development toolchain

Which components shall be installed? If unsure press ENTER []

C:\Users\Administrator>gem install rails
Building native extensions. This could take a while...
Successfully installed websocket-driver-0.7.5
Building native extensions. This could take a while...
Successfully installed nio4r-2.5.8
Successfully installed actioncable-7.0.2
Successfully installed rails-7.0.2
Parsing documentation for websocket-driver-0.7.5
Installing ri documentation for websocket-driver-0.7.5
Parsing documentation for nio4r-2.5.8
Installing ri documentation for nio4r-2.5.8
Parsing documentation for actioncable-7.0.2
Installing ri documentation for actioncable-7.0.2
Parsing documentation for rails-7.0.2
Installing ri documentation for rails-7.0.2
Done installing documentation for websocket-driver, nio4r, actioncable, rails after 2 seconds
4 gems installed

C:\Users\Administrator>rails -v
Rails 7.0.2

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