How to set environment variables from appsettings.json for .net core console app?

Question

I'm working with a C# class that reads from appsettings using

Environment.GetEnvironmentVariable("setting")

I want to make another console program (.net core 3.0) that reads settings from appsettings.json and loads them into environment variables.

static void Main(string[] args)
{
     var builder = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .AddEnvironmentVariables();

            IConfiguration config = builder
                .Build();

    var businessLogic = new BusinessLogic(); // uses GetEnvironmentVariable to get configuration
}

In my business logic class, the environment variables aren't getting pulled back correctly. What might be the problem?

appsettings.json is in this format:

{
    "SETTING" : "setting value"
}

Answer 1

Environment.GetEnvironmentVariable("setting") will always try to read the data from an environment variable, not from your loaded config.

You need to change your BusinessLogic class to accept the config object you built and use that to access the settings. An example:

public class BusinessLogic
{
    public BusinessLogic(IConfiguration config)
    {
        var value = config.GetValue<string>("SETTING");
    }
}

In this example value will contain the correct value of SETTING if it was last set in appsettings.json or using an environment variable.