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class String
  def dasherize
    to_s.gsub '_', '-'
  end
  
  def switchify
    length > 1 ? "--#{dasherize}" : "-#{self}"
  end
end

class Hash
  def switchify
    inject [] do |args, (key, value)|
      next args unless value
      args << key.to_s.switchify
      args << (value === String ? value.inspect : value.to_s) unless value === true
      args
    end
  end
end

h = { :config => 'foo.ini', :verbose => true, :with_foo_bar => false, :with_some_coolness => true, :T => true }

p h.switchify
# => ["--config", "foo.ini", "--verbose", "--with-foo", "-T"]

p h.switchify.join(' ')
# => --config foo.ini --verbose --with-foo -T