function solution(input, cmd)
  -- parse all <name>="<bla>" (key/value pairs)
  local i, values, pos = 0, {}, {}
  local j, k, v
  while true do
    j, i, k, v = string.find(input, '([a-zA-Z]+)="([^"]*)"', i+1)
    if not j then break end
    values[k] = v
    pos[k] = {j+#k+2, i}
  end

  -- cmd = "copy <key1> to <key2>"
  local key1, key2 = cmd:match("copy ([%S]+) to ([%S]+)")
  if not key1 then error("Could not parse command: "..cmd) end

  -- look up key1
  local value = values[key1]
  if not value then error("attribute "..key1.." not found") end

  -- paste after key2 in input (removing the old value)
  if not pos[key2] then error("attribute "..key2.." not found") end
  local i, j = unpack(pos[key2])
  input = input:sub(1, i-1)..value..input:sub(j)

  return input
end