Read environment variables in ASP.NET Core - asp.net

Question

Running my ASP.NET Core application using DNX, I was able to set environment variables from the command line and then run it like this:
set ASPNET_ENV = Production
dnx web
Using the same approach in 1.0:
set ASPNETCORE_ENVIRONMENT = Production
dotnet run
does not work - the application does not seem to be able to read environment variables.
Console.WriteLine(Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT"));
returns null
What am I missing?

Answer 1

Your problem is spaces around =.
This will work (attention to space before closing quote):
Console.WriteLine(Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT "));
The space after ASPNETCORE_ENVIRONMENT in this code is not a typo! The problem in the question was having extra space (in SET...), so you must use the same space in GetEnvironmentVariable().
As noted by Isantipov in a comment, an even better solution is to remove the spaces entirely from the SET command:
set ASPNETCORE_ENVIRONMENT=Production

Answer 2

This should really be a comment to this answer by #Dmitry (but it is too long, hence I post it as a separate answer):
You wouldn't want to use 'ASPNETCORE_ENVIRONMENT ' (with a trailing space) - there are features in ASP.NET Core which depend on the value of 'ASPNETCORE_ENVIRONMENT'(no trailing space) - e.g. resolving of appsettings.Development.json vs appsettings.Production.json. (e.g. see Working with multiple environments documentation article
And also I guess if you'd like to stay purely inside ASP.NET Core paradigm, you'd want to use IHostingEnvironment.Environment(see documentation) property instead of reading from Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") directly (although the former is of course set from the latter). E.g. in Startup.cs
public class Startup
{
//<...>
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
Console.WriteLine("HostingEnvironmentName: '{0}'", env.EnvironmentName);
//<...>
}
//<...>
}

Answer 3

If you create the Environment variables at runtime during development then you will get null every time. You have to restart the visual studio because VS read EV at startup only.