使用 Elixir 格式化日期

Question

I'm trying to format the Timex module to look a certain way. I'm trying to get today's date. but I want it formatted like this:

2017/12/12.

year/mn/day

In ruby I would go to the strftime class but I'm not sure how to do this with Elixir:

Current attempt:

Timex.local => #DateTime<2017-12-12 19:57:17.232916-05:00 EST America/Detroit>

How can I take that and format it how I specified?

Answer 1

Timex is a third-party library that was created in the era when Elixir had no good support for dates/times. Nowadays, there is DateTime native class in the core, so I am unsure why do you want to use Timex at all.

In any case, DateTime is a struct:

iex|1 ▶ today = DateTime.utc_now
#⇒ #DateTime<2017-12-13 07:22:58.290075Z>
iex|2 ▶ [today.year, today.month, today.day]
#⇒ [2017, 12, 13]
iex|3 ▶ Enum.join [today.year, today.month, today.day], "/"
#⇒ "2017/12/13"

---

To pad with leading zeroes for "2018/1/1":

iex|4 ▶ with {:ok, today} <- Date.new(2018, 1, 1) do
...|4 ▶   [today.year, today.month, today.day]
...|4 ▶   |> Enum.map(&to_string/1)
...|4 ▶   |> Enum.map(&String.pad_leading(&1, 2, "0"))
...|4 ▶   |> Enum.join("/")
...|4 ▶ end
#⇒ "2018/01/01"

Answer 2

If you want to do this without an external library, you can use io_lib:format/2 to pad the integers with zeroes where necessary like this:

iex(1)> date = Date.utc_today
~D[2017-12-13]
iex(2)> :io_lib.format("~4..0B/~2..0B/~2..0B", [date.year, date.month, date.day]) |> IO.iodata_to_binary
"2017/12/13"
iex(3)> {:ok, date} = Date.new(2018, 1, 1)
{:ok, ~D[2018-01-01]}
iex(4)> :io_lib.format("~4..0B/~2..0B/~2..0B", [date.year, date.month, date.day]) |> IO.iodata_to_binary
"2018/01/01"
iex(5)> {:ok, date} = Date.new(1, 1, 1)
{:ok, ~D[0001-01-01]}
iex(6)> :io_lib.format("~4..0B/~2..0B/~2..0B", [date.year, date.month, date.day]) |> IO.iodata_to_binary
"0001/01/01"

Answer 3

你可以这样做来添加零

Timex.local |>  Timex.format!("{YYYY}/0{M}/0{D}") => "2017/01/01"

Answer 4

Elixir 1.11 has Calendar.strftime/3 built-in for your strftime needs.

Calendar.strftime(~U[2019-08-26 13:52:06.0Z], "%y-%m-%d %I:%M:%S %p")
"19-08-26 01:52:06 PM"

Answer 5

So it appears the Timex Module has a format!/2 function which will return a string of what ever date you pass to it.

Here is what I came up with: Timex.local |> Timex.format!("{YYYY}/{M}/{D}") => "2017/12/12"

Answer 6

The answer to add 0 padding is incorrect and will always pad 0s even if it does not require it. The correct way to pad 0s is as follows:

Timex.local |>  Timex.format!("{YYYY}/{0M}/{0D}") => "2017/01/01"

Answer 7

As of Elixir 1.11 you can do this sanely with a date formatter in the standard library's Calendar module:

https://hexdocs.pm/elixir/1.13.0/Calendar.html#strftime/3

DateTime.utc_now()
|> Calendar.strftime("%Y/%m/%d")

"2022/01/12"