Get variable name from variable

gistfile1.rb

foo = 'i ama string'

var_type = defined? foo 

variable_list = case var_type
when "local-variable" 
  local_variables
when "instance-variable" 
  instance_variables
when "global-variable"
  gloval_variables
else
  []
end

var_name = variable_list.detect {|v| eval(v.to_s) == foo} 

puts "The value of the '#{var_name}' variable is '#{foo}'"
#=> The value of the 'foo' variable is 'i ama string'