Set ASPNETCORE_ENVIRONMENT variable from the application code

Program.cs

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

namespace EnvironmentSample
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Assuming args[0] has environment name
            // Command to run: {envName} should be replaced by env name
            // dotnet run {envName}
            var environment = string.IsNullOrEmpty(args[0]) ? "Production" : args[0].Trim();
            CreateHostBuilder(args).UseEnvironment(environment).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}