a.rb

require 'debug_inspector'

def a(a)
  b(1)
end

def b(b)
  c(2)
end

def c(c)
  RubyVM::DebugInspector.open do |i|
    n = 0
    loop do
      begin
        b = i.frame_binding(n)
      rescue ArgumentError
        break
      end

      if b
        puts(b.eval("local_variables").each_with_object({}) do |v, h|
          h[v] = b.local_variable_get(v)
        end)
      end

      n += 1
    end
  end
end

a(0)