How to get Line Numbers in Console Outputs in Elixir

Question

I need to get line numbers for IO.puts or IO.inspect or any other kind of output that appears on elixir console for the purpose of debugging. Is there an in-built feature for this? Or is there any other easy way to achieve the same?

P.S: By Line Number for IO.puts, I mean the line where IO.puts is written in the code.

Brouhaha

Answer 1

You're probably looking for __ENV__, which will give you access to the current file and line (among other things). You could do something like this:

Logger.debug("#{__ENV__.file}:#{__ENV__.line}: #{inspect some_value}")

Edit: as José suggested in the comments, the better way to do this is to use the metadata feature of logger. At the moment, you can only add the :module, :function and :line keys:

# config/config.exs

config :logger, :console, metadata: [:module, :function, :line]

However, I made a PR to add the :file key as well. It is already merged and should be released with the next version of Elixir. With the new version you can do

# config/config.exs

config :logger, :console, metadata: [:file, :line]

Virology

Keep in mind that Logger already includes both file and line in the metadata. You can include it in your reports by adding both file and line to your metadata configuration in logger. – Faviolafavonian

@JoséValim you mean this right? config :logger, :console, metadata: [:module, :function, :line] – Virology

Unfortunately it seems impossible to add the file this way. – Virology

:file works, but it holds the complete path. How would I drop the path and only log the filename and extension? – Kasher

AFAIK you need to do this manually, as in my first example. You can write a macro to avoid repetition, there you can use __CALLER__ instead of __ENV__ which should give you the file and line at the point where the macro was called. To extract just the filename you can use Path.basename/1, but be aware that the generated output will be ambiguous for equally nsmed files in differing directories. – Virology

I was wondering why the only file I see is the logger.ex. Then I changed an IO.inspect to Logger.debug and it started to show the actual file the log was put into. Any way to make that work for IO.inspect as expected? – Workman

The OP says he's looking for IO.puts but isn't this for the logger? Isn't logger a tottaly different thing? Sorry if I'm wrong. I also have the same question as the OP re: IO.puts. This doesn't appear to solve that. – Demigod

@MoteZart it does not matter how you present the output, __ENV__ contains the file and line number of the currently executing code. If you happen to use Logger, it's more convenient if you want file and line numbers on all debugging output to just configure that in one place. – Virology