Q:

Setting environment variables in .NET Core 2.0

I am trying to setting up multiple environments in my .NET Core 2.0 application. See my code below.
Configuration file (Launch.JSON)
"configurations": [
    {
        "name": ".NET Core Launch (web)",
        "type": "coreclr",
        "request": "launch",
        "preLaunchTask": "build",
        // If you have changed target frameworks, make sure to update the program path.
        "program": "${workspaceRoot}/my.api/bin/Debug/netcoreapp2.0/my.api.dll",
        "args": [],
        "cwd": "${workspaceRoot}/my.api",
        "stopAtEntry": false,
        "requireExactSource": false,
        "internalConsoleOptions": "openOnSessionStart",
        "launchBrowser": {
            "enabled": true,
            "args": "${auto-detect-url}",
            "windows": {
                "command": "cmd.exe",
                "args": "/C start ${auto-detect-url}"
            },
            "osx": {
                "command": "open"
            },
            "linux": {
                "command": "xdg-open"
            }
        },
        "env": {
            "ASPNETCORE_ENVIRONMENT": "Development"
        },
        "sourceFileMap": {
            "/Views": "${workspaceRoot}/Views"
        }
    },
    {
        "name": ".NET Core Attach",
        "type": "coreclr",
        "request": "attach",
        "processId": "${command:pickProcess}"
    }
]

Program.cs
public class Program
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .Build();
}

StartUp.cs
public class Startup
{
    public IContainer ApplicationContainer { get; private set; }
    private IHostingEnvironment HostingEnvironment { get; set; }
    public IConfigurationRoot Configuration { get; }
    private string ConnectionString
    {
        get
        {
            return this.HostingEnvironment.IsDevelopment() ? Configuration.GetConnectionString("DefaultConnection") : Configuration.GetConnectionString("Production");
        }
    }

    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.Development.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.Azuredev.json", optional: true, reloadOnChange: true)
            .AddEnvironmentVariables();

        Configuration = builder.Build();

        this.HostingEnvironment = env;

        System.Console.WriteLine(env.EnvironmentName); // Here it always give me Production.
    }

My issue
I tried to use command line like dotnet run --environment "Development"
So, it should run on Development Environment, but it always runs with Production, (look I have added console.writeline in my startup.cs file)
Now the strange thing is that if I use F5 to Debug then it runs perfectly with the development environment.

A:

You can update your launchsettings.json to include a 'Development' profile and then run:
dotnet run --launch-profile "Development"

For further details on configuration of the launchSettings.json file see Working with multiple environments
Note that the commandName would probably need to be "Project" (I haven't really tried this much). Example launchSettings.json as follows:
{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:19882/",
      "sslPort": 0
    }
  },
  "profiles": {
    "Development": {
      "commandName": "Project",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }
  }
}

A:

Finally I have done it...
Let’s look at how I achieved this.

I have added all my profile settings in launchSettings.JSON
Program.cs remains same as I added in my question.
Updated startup.cs (see below)
CLI for run it via terminal is also different.

Now first let's see my project structure.

Code in my launchSettings.json
{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:40088/",
      "sslPort": 0
    }
  },
  "profiles": {
    "Development": {
      "commandName": "Project",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },
    "Azuredev": {
      "commandName": "Project",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Azuredev"
      }
    }
  }
}

Code in launch.json
{
"version": "0.2.0",
"configurations": [
        {
            "name": ".NET Core Launch (web)",
            "type": "coreclr",
            "request": "launch",
            "preLaunchTask": "build",
            // If you have changed target frameworks, make sure to update the program path.
            "program": "${workspaceRoot}/my.api/bin/Debug/netcoreapp2.0/my.api.dll",
            "args": [],
            "cwd": "${workspaceRoot}/my.api",
            "stopAtEntry": false,
            "requireExactSource": false,
            "internalConsoleOptions": "openOnSessionStart",
            "launchBrowser": {
                "enabled": true,
                "args": "${auto-detect-url}",
                "windows": {
                    "command": "cmd.exe",
                    "args": "/C start ${auto-detect-url}"
                },
                "osx": {
                    "command": "open"
                },
                "linux": {
                    "command": "xdg-open"
                }
            },
            "sourceFileMap": {
                "/Views": "${workspaceRoot}/Views"
            }
        },
        {
            "name": ".NET Core Attach",
            "type": "coreclr",
            "request": "attach",
            "processId": "${command:pickProcess}"
        }
    ]
}

startup.cs
    public IConfigurationRoot Configuration { get; }

    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
            .SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true)
            .AddEnvironmentVariables();

        Configuration = builder.Build();

        this.HostingEnvironment = env;
    }

After this all changes, my API is working fine with both the F5 debug option as well as CLI terminal.
To launch the application from the command line, use these keywords:
dotnet run --launch-profile "Development"

OR
dotnet run --launch-profile "Azuredev"

