Dynamic Gemfile Sources

gem_sources.yml

---
gem_sources:
  - 'https://rubygems.org'
  - 'http://rubygems.org'

Gemfile

# Dynamically load gem sources from YAML config file
require 'yaml'
# See if we have a custom gem_sources.yml file, if not use the .example default.
if File.exist? File.expand_path("../config/gem_sources.yml", __FILE__)
  gem_sources_file = File.expand_path("../config/gem_sources.yml", __FILE__)
  puts "NOTE: Using the following gem sources from `config/gem_sources.yml`:"
  @custom_gem_source = true
else
  gem_sources_file = File.expand_path("../config/gem_sources.yml.example", __FILE__)
end
sources_yaml = YAML::load(File.read(gem_sources_file))
sources_yaml['gem_sources'].each do |source_str|
  puts source_str if @custom_gem_source
  source source_str
end

# Put your gems below as usual