How to create a gem

From WhyNotWiki

Aliases: How to make a gem, Packaging gems, Gem creation

Gems  edit   (Category  edit)

Contents 1 The steps 2 Test installing a gem 3 Publish your gem 4 Is there a way to have RubyGems execute some 'post-install' script after it installs your gem? 4.1 post-install script idea 1 4.2 post-install script idea 2 4.3 Adding your gem's executable directory to user's path

[edit] The steps

1. Write your gem specification
2. Build your gem with a rake task
3. Test installing your gem
4. Publish your gem

[edit] Test installing a gem

> sudo gem install --local pkg/OurExtensions-0.0.1.gem
  --rdoc  # So you can test that the rdoc installs properly
  --test  # So you can ensure that all the tests pass still
  --force # In case it's already installed
Attempting local installation of 'pkg/OurExtensions-0.0.1.gem'
Successfully installed OurExtensions, version 0.0.1
Installing RDoc documentation for OurExtensions-0.0.1...
[runs tests for you...]

(Hint: You can always do --install-dir ./some_local_dir/ if you don't have sudo.)

This should huncover any installation problems that your users might have. If you specified an incorrect autorequire file in your gemspec, for example, you will find out about it here.

And if you want to clean up afterwards...

> sudo gem uninstall OurExtensions
Attempting to uninstall gem 'OurExtensions'
Successfully uninstalled OurExtensions version 0.0.1

[edit] Publish your gem

Put it on RubyForge!

...

[edit] Is there a way to have RubyGems execute some 'post-install' script after it installs your gem?

No, not that I know of.

What would you want your 'installer' script to do?

• Copy files to locations that RubyGems doesn't know about (like /home/tyler/.vim or /usr/share/vim/vimfiles in the case of vim-ruby)
• Add a line to the user's ~/.bash_profile or equivalent
• Create a ~/.your_gem_name_rc file
• ...

Since RubyGems can't do it for you, you'll have to either

• Instruct your users how to install/configure your gem (the steps that come after gem install)
• Provide an installer script so they only have to run one additional command after the gem install

[edit] post-install script idea 1

It looks like that's the route vim-ruby chose to go... Their installation directions go like this:

# gem install vim-ruby --remote
# vim-ruby-install.rb

vim-ruby-install.rb is an executable that RubyGems installed for you and placed at /usr/bin/vim-ruby-install.rb (or equivalent) so it should be in your path already.

If you create an installer script, keep in mind:

• Give it a unique name. You don't want to conflict with/overwrite any other files in /usr/bin ...

bin/_svn_command_post_install

#!/usr/bin/env ruby

require 'fileutils'
if ARGV.include?('--dry-run')
  include FileUtils::DryRun
else
  include FileUtils::Verbose
end

bin_dir = File.expand_path(File.dirname(__FILE__))
chmod 0755, Dir["#{bin_dir}/*"]

path_command = "export PATH=`ls -dt --color=never /usr/lib/ruby/gems/1.8/gems/svn-command* | head -n1`/bin:$PATH"
system "grep gems/svn-command ~/.bash_profile || " +
       "echo '#{path_command}' >> ~/.bash_profile"

[edit] post-install script idea 2

/usr/lib/ruby/gems/1.8/gems/railsbench-0.9.1/INSTALL

Since gem packages don't support running postinstall scripts, you will
need to make the scripts executable by running

   sudo railsbench postinstall

[edit] Adding your gem's executable directory to user's path

/usr/lib/ruby/gems/1.8/gems/railsbench-0.9.1/INSTALL

Alternatively, add the railsbench script directory to your search
path. The exact place can be found running

    railsbench base

which prints the script directory path. Another option is to run

    eval `railsbench path`

> railsbench path
PATH=/usr/lib/ruby/gems/1.8/gems/railsbench-0.9.1/script:$PATH
> railsbench base
railsbench is installed in: /usr/lib/ruby/gems/1.8/gems/railsbench-0.9.1

/usr/lib/ruby/gems/1.8/gems/railsbench-0.9.1/bin/railsbench

RAILSBENCH_BASE = File.expand_path(File.dirname(__FILE__) + '/..')

case real_cmd
when 'base'
  puts "railsbench is installed in: #{RAILSBENCH_BASE}"
  exit
when 'help', 'readme'
  File.open("#{RAILSBENCH_BASE}/README").each_line{|l| puts l}
  exit
when 'path'
  puts "PATH=#{RAILSBENCH_BASE}/script:$PATH"
  exit