How to log to stderr?

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,
21

Ah - I did see this tidbit - but then went back to Elixir doc.

And I did not know about :logger.get_handler_config(:default)

Now I hope I can figure it out.

Thank you very much!

EDIT

The following does work for me (Elixir 1.15.7 (compiled with Erlang/OTP 26):

{:ok, handler_config} = :logger.get_handler_config(:default)

updated_config = 
  handler_config
  |> Map.update!(:config, fn config ->
    Map.put(config, :type, :standard_error)
  end)

:ok = :logger.remove_handler(:default)
:ok = :logger.add_handler(:default, :logger_std_h, updated_config)

require Logger
Logger.error("Hello error on stderr")
Logger.debug("Hello debug on stderr")
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22

My goal was not to write to STDERR - rather to have the standard logger behave sensibly. (And I understand my definition of sensible may not match typical BEAM use cases).

Maybe I’ll provide more context:

I am writing a tiny app that will talk to a legacy XML API (a get-to-know Elixir/LiveView project).
I started with the XML API interface. Request payloads are rendered using EEx templates. I liked how I could pattern match to select the appropriate template and then render it injecting required values. Once I had that ready I whipped up an .exs script that reads key value pairs (from System.argv). I could fire it off and render requests to STDOUT. The next step was piping to | curl -d@- -XPOST http://... The server complained about illegal input. After a bit of poking I realized log messages went to STDOUT rather than STDERR so I was feeding not only XML but logger output to the remote host.

And hence my question about having logger write to STDOUT.

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