Inside IEx when I run Process.whereis(:standard_error) I got the PID, but not when I run Process.whereis(:standard_io) . Who knows why should this happen and how to get the PID from : stdio ?

That is because the i/o system and the error handling behave in different ways. For the error handling there is a central server process registered under the name :standard_error but this is not case for the i/o system. The best way to view an erlang/elixir system to think OS with many tasks and eac…

[image] rvirding: Strangely enough this was the first time much of the rationale for erlang was actually described, about 10-15 years after it was designed. This was because we had so thought about it and discussed it we felt it was self-evident that this was the way it should be done. We found …

Just went through the erlang rationale document and I wish there was more where that came from! Thank you very much for sharing this

@rvirding it’s possible to do something similar to this but with :stdio? Process.unregister(:standard_error) {:ok, dev} = StringIO.open("") Process.register(dev, :standard_error) Code.eval_file(exercise, File.cwd!) |> elem(0) captured = StringIO.flush(dev) Process.unregister…

Not directly that I know of. Stdio doesn’t work through a registered process but uses the default process group leader. This is where it goes when you read/write without giving an i/o device.

To exemplify @rvirding ’s reply, :standard_io translates to Process.group_leader, which can change per process. :standard_error is a local process though. Here is an interesting post on the different things that are done with the group leader: REPL? A bit more (and less) than that

Fred’s blog gives a very good description of how it looks and why it looks like that. We had OS inspired thinking behind the design of the system. That’s why I like to say that Erlang is not a language with concurrency but a OS with a language. Elixir buys straight into this though iex is not quite …

Elixir Programming Language Forum

Getting stdio process ID

Questions & Help Questions

edwinallenz September 11, 2019, 6:13pm 4

That’s a great response for a simple question Robert, thank you so much.