Checks your Gemfile for public gems on rubygems.org

verify_gems.rb

#!/usr/bin/env ruby

# This class will check search rubygems.org for all gems in a given Gemfile.
# If a given gem is not available on rubygems.org, it will tell you such.
class VerifyGems
  def initialize _file, _source
    @file   = _file   || 'Gemfile'
    @source = _source || 'http://rubygems.org'
    @gems   = []
    @verbose = false

    unless File.exists?(@file)
      puts "Please supply a Gemfile to evaluate."
      exit
    end
  end

  def gem name, version = nil, options = {}
    @gems << name
  end

  def group *args; end

  def source *args; end

  def verbose?
    @verbose
  end

  def verify
    eval(File.new(@file).read)

    regex = @gems.map{|name| "^#{name}$"}.join("|")

    query = `gem query -r -n '#{regex}' --clear-sources --source #{@source}`

    @gems.each do |name|
      if query.match /#{name}/
        puts "Found #{name} on #{@source}" if verbose?
      else
        puts "#{name} is not on #{@source}"
      end
    end
  end
end

VerifyGems.new(ARGV.shift, ARGV.shift).verify

may make this a gem plugin. Its useful when you have your own gemserver and want to know which ones are not publicly available on the main gemserver.