I don't see what is wrong here

require "sinatra"

def load_signature(index)
  # Code omitted for brevity
end

def save_signature(signature)
  # Code omitted for brevity
end

def update_signature(index, signature)
  # Code omitted for brevity
end

# Deletes the line at the given index and re-saves the file.
def delete_signature(index)
  lines = File.readlines("signatures.txt")
  index = index.to_i
  lines.delete_at(index)
  File.open("signatures.txt", "w") do |file|
    file.puts lines
 end
end

get "/signatures/new" do
  # Code omitted for brevity
end

get "/signatures/:index" do
  @index = params[:index]
  @signature = load_signature(@index)
  erb 'show'.to_sym
end

delete "/signatures/:index" do
  @index = params[:index]
  @signature = delete_signature(@index)
  redirect "/signatures/new"
end