function split(str, sep, plain)
  local b, res = 1, {}
  while b <= #str do
    local e, e2 = string.find(str, sep, b, plain)
    if e then
      res[#res + 1] = string.sub(str, b, e-1)
      b = e2 + 1
    else
      res[#res + 1] = string.sub(str, b)
      break
    end
  end
  return res
end

function split_first(str, sep, plain)
  local e, e2 = string.find(str, sep, nil, plain)
  if e then
    return string.sub(str, 1, e - 1), string.sub(str, e2 + 1)
  end
  return str
end

local unpack = unpack or table.unpack

function usplit(...) return unpack(split(...)) end