Ruby gems in stand-alone ruby scripts

Question

This is a really basic ruby gems question. I'm familiar with writing simple ruby scripts like this:

#!/usr/bin/ruby
require 'time'
t = Time.at(123)
puts t

Now I'd like to use my own ruby gem in my script. In my rails project I can simply require 'my_gem'. However this doesn't work in a stand-alone script. What's the best/proper way to use my own gem in a stand-alone ruby script?

Answer 1

You should be able to simply require it directly in recent versions of Ruby.

# optional, also allows you to specify version
gem 'chronic', '~>0.6'

# just require and use it
require 'chronic'
puts Chronic::VERSION  # yields "0.6.7" for me

If you are still on Ruby 1.8 (which does not require RubyGems by default), you will have to explicitly put this line above your attempt to load the gem:

require 'rubygems'

Alternatively, you can invoke the Ruby interpreter with the flag -rubygems which will have the same effect.

See also:

• http://docs.rubygems.org/read/chapter/3#page70
• http://docs.rubygems.org/read/chapter/4

Answer 2

You could use something like this. It will install the gem if it's not already installed:

def load_gem(name, version=nil)
  # needed if your ruby version is less than 1.9
  require 'rubygems'

  begin
    gem name, version
  rescue LoadError
    version = "--version '#{version}'" unless version.nil?
    system("gem install #{name} #{version}")
    Gem.clear_paths
    retry
  end

  require name
end

load_gem 'your_gem'

Answer 3

It is to be noted that bundler itself can deal with this. It's particularly interesting since bundler ships with Ruby by default since version 2.6, and you don't need to install it manually anymore.

The idea is:

1. to require bundler/inline at the top of your script,
2. to use the gemfile method, and declare the gems you need inside a block, like you'd do in a Gemfile,
3. after the end of this section, your gems are available!

For instance:

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'rainbow'
end

# From here on, rainbow is available so I can 
# print colored text into my terminal

require 'rainbow'
puts Rainbow('This will be printed in red').red

The official documentation can be found on bundler website: bundler in a single file ruby script

Answer 4

Installing gems with something like the following should work. Be mindful of whether gems should be installed as part of system ruby or a user's.

#!/usr/bin/env ruby

require 'rubygems'

def install_gem(name, version=Gem::Requirement.default)
  begin
    gem name, version
  rescue LoadError
    print "ruby gem '#{name}' not found, " <<
      "would you like to install it (y/N)? : "
    answer = gets
    if answer[0].downcase.include? "y"
      Gem.install name, version
    else
      exit(1)
    end
  end
end

# any of the following will work...
install_gem 'activesupport'
install_gem 'activesupport', '= 4.2.5'
install_gem 'activesupport', '~> 4.2.5'

# require as normal (since not all gems install & require with same name) ...
require 'active_support/all'

...

Answer 5

I'm not sure if I understood your question right, but perhaps you don't have a gem, even if you write it (you are a beginner, so perhaps you misunderstood the concept of gems).

Just to be sure: You have a gemspec for your gem? If not, then you have no gem, but a single script.

When you want your own script inside another script, you may just do:

require 'my_script'

With ruby 1.8 this works fine, if my_script.rb is in the same folder as your main script. With ruby 1.9+ you can use:

require_relative 'my_script'

There is no need of a gem in this case.