System.get_env!/1 that raises if the ENV var is not present

[Paul Smith]

In almost all cases I would like to treat a missing ENV var as an error and blow up immediately so I know what's wrong. The current behavior of `System.get_env/1` returns nil, which isn't very helpful and can be hard to trace. Having a version that raises would make debugging a lot easier. Right now I created my own function in the app that calls System.get_env and raises if the value is nil, I think this isn't very ideal.

I'd be happy to submit a PR if this is something that should be in Elixir!

- Paul

[Theron Boerner]

I would prefer if it returned an {:ok, _} or {:error, _} tuple, though I don't know about everyone else.

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[José Valim]

System.get_env only returns a string or nil, so it is easily distinguishable without a need for a tuple. The advantage of returning nil is that || can be easily used to provide a default value, which is a common thing to do.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Paul Smith (thoughtbot)]

Right, I can definitely see the advantage of returning nil, so I’m suggesting adding a new function that raises (hard to see the ! in the subject).

Would you be up for adding a new function that raises?

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[Paul Smith]

Maybe a better name would be `System.fetch_env!/1` to match the Dict module a bit better?

[Peter Hamilton]

How about we make System.env a Dict, so you can do: Dict.fetch!(System.env, :foo)

On Wed, Nov 4, 2015, 8:04 AM Paul Smith <pa...@thoughtbot.com> wrote:

Maybe a better name would be `System.fetch_env!/1` to match the Dict module a bit better?

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[Paul Smith]

You bring up a good point. That might be the best solution, which is great because you can already do that!

Dict.fetch!(System.get_env, "MY_VAR") 

This might be better than adding a new function that basically does exactly this

[Ben Wilson]

Yeah I like the pattern of

System.get_env |> Map.fetch!("MY_ENV_VAR")

a lot better than a new function that raises by default

[Wojtek Mach]

Hi all,

System.get_env |> Map.fetch!("FOO")

does the trick, however when it raises an error it puts the entire ENV into the exception message which may or may not be a good thing. I guess locally it's not a big deal and it helps debugging however I'd be afraid of exposing the contents of ENV (which often has some secrets) in a CI/prod. Again, perhaps it's not a big concern.

I've been using following code on my projects:

secret_key_base: System.get_env("SECRET_KEY_BASE") || raise("ENV variable not set: SECRET_KEY_BASE")

It's a bit tedious to write it down every single time, but that's OK. Still, I think System.get_env!/1 or System.fetch_env!/1 would be a good addition to the stdlib and would encourage folks to "fail fast" when the application boots.

[Paul Smith]

That's a good point. I've also noticed that System.get_env sometimes picks ENV variables up that Map.fetch! does not. So sometimes I have to do what you're doing with the raise.

Now that I've tried the Map.fetch! Way of doing things and it doesn't work that well, I think it would be nice to have System.get_env! added. What does everyone else think?

Either way it would probably be good to make System.get_env work more reliably so you can use Map.fetch! Maybe what's happening now is a bug? I'll open up an issue about that next week just in case.

[Matthew Wean]

I would love to have a raising version too. As it stands, I often get confusing errors deep in the system because of missing ENV variables. Is this something we can add?

[José Valim]

Please open up an issue. We just need to figure out if the name will be get_env! or fetch_env! (I could argue any).

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

On Thu, Dec 29, 2016 at 10:15 PM, Matthew Wean <matthe...@gmail.com> wrote:

I would love to have a raising version too. As it stands, I often get confusing errors deep in the system because of missing ENV variables. Is this something we can add?

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[Michał Muskała]

I guess the standard set of get + fetch + fetch! would be the best solution. It would be the least surprising since it works like this nearly everywhere.

Michał.

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