In Ruby 2.2, the binding object gives us access to a method #local_variables which returns the symbol names of the binding’s local variables. We can see this in action with

def square(x)
  puts binding.local_variables.inspect
  x.times do |a|
    puts binding.local_variables.inspect
  end
  z = x * x
  puts binding.local_variables.inspect
  z
end
square(2)

which results in

[:x, :z]
[:a, :x, :z]
[:a, :x, :z]
[:x, :z]
=> 4

source