app.rb

get '/customer/:cid' do
  # Output params hash in bash
  puts params.inspect    
  
  # Retrieve customer ID from params hash  
  cid = params[:cid]
  
  # Retrieve customer object from Stripe API
  # Store customer object in an instance variable
  @customer = Stripe::Customer.retrieve(cid)
  
  # Show customer.erb template to user
  erb :customer
end