Overriding appsettings.json Via Command Line

In a previous post, Flexible Leveraging Of appsettings.json In .NET Applications, we talked about how to use the .NET configuration infrastructure via the options pattern to set and load setting.

In a subsequent post, Setting The Staging & Production Environments During Development, we talked about how to set the environment of an application so as to determine the settings to be loaded.

In this post, we will look at how to override the settings in the json files via the command line.

As a recap, the test application has the following settings:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "SystemSettings": {
    "ForegroundColour": "White",
    "BackgroundColour": "Black"
  }
}

And we have the following web API:

using ApplicationSettings.Properties;
using Microsoft.Extensions.Options;

var builder = WebApplication.CreateBuilder(args);

// Configure options DI
builder.Services.AddOptions<SystemSettings>()
    .Bind(builder.Configuration.GetSection(nameof(SystemSettings)));

var app = builder.Build();

app.MapGet("/", (IOptions<SystemSettings> options) =>
{
    var settings = options.Value;
    return settings;
});

app.Run();

If we run this, we get the following result:

It is possible to override this at runtime, by passing the required settings as parameters via the command line.

You do this as follows:

dotnet run --SystemSettings:ForegroundColour=Maroon --SystemSettings:BackgroundColour=Pink

Here we are setting the ForegroundColour and BackgroundColour at the command line.

Of note is that for hierarchical settings, we denote the hierarchy with the colon : , as shown above.

This should result in the following:

TLDR

You can override settings in appsettings.json by passing new ones via command line.

The code is in my GitHub.

Happy hacking!