Method to find the first uncommon point in the call stack of a line of Ruby

puts_first_common_point.rb

def puts_first_common_point
  if $previous_caller
    this_caller = caller[1..-1]
    this_caller.each_with_index do |line, i|
      if $previous_caller[i] == line
        puts line
      else
        puts 'FIRST DIFFERENT LINE:'
        puts "Previous: #{$previous_caller[i]}"
        puts "This: #{line}"
        exit!
      end
    end
  else
    $previous_caller = caller[1..-1]
  end
end