COPY xx_table ... FROM stdin
4       33380   N      N
4       33380   N      N
.

IO.stream(:stdio, :line)
|> Stream.transform(false, fn line, skipping ->
  cond do
    !skipping && String.starts_with?(line, "COPY") -> {[{true, line}], true}
    skipping && line == "\.n" -> {[{true, line}], false}
    true -> {[{skipping, line}], skipping}
  end
end)
|> Stream.filter(fn {skipping, _} -> !skipping end)
|> Stream.map(fn {_, line} -> line end)
|> Stream.into(IO.stream(:stdio, :line))
|> Stream.run()

IO.stream(:stdio, :line)
|> Stream.into(IO.stream(:stdio, :line))
|> Stream.run()