checkinstall_wirble.rb

#!/usr/bin/env ruby
#
# Checks to see if the wirble gem is installed and
# installs it for you if it is not already installed.

def gem_list
  @gem_list ||= `gem list`
end

def gem_name_re
  /\A[^\w_-]+\z/
end

def validate(name)
  if gem_name_re === name
    raise "Did you use the correct gem name?"
  end
end

def check_install(gem_name)
  validate(gem_name)

  unless /#{gem_name}/ === gem_list
    if exec "gem install #{gem_name}"
      @gem_list << gem_name
    end
  end
end

check_install("wirble")