I have a C# console program that prints an App.config value. Can I override this value from an environment variable?
Example App.config:
<appSettings>
<add key="TestKey" value="Foo"/>
</appSettings>
Example Code:
Console.WriteLine($"Key: {ConfigurationManager.AppSettings["TestKey"]}");
I tried just setting the Key name but that obviously doesn't work:
C:\> set TestKey=Bar
C:\> ConsoleApp2.exe
Key: Foo
The ConfigurationManager class doesn't do that for you, it will only read from your app config. To fix this, you can use a function to get the variable and use that instead of calling ConfigurationManager.AppSettings directly. This is good practice to do anyway as it means you can easily move your config into a JSON file or a database and you won't need to update every usage of the old method.
For example:
public string GetSetting(string key)
{
var value = Environment.GetEnvironmentVariable(key);
if(string.IsNullOrEmpty(value))
{
value = ConfigurationManager.AppSettings[key];
}
return value;
}
In .net 4.7.1 you can use ConfigurationBuilders to accomplish this.
in netcore (aspnetcore) you can override settings in environments https://github.com/dotnet/AspNetCore.Docs/issues/11361#issuecomment-471680877
need use prefix ASPNETCORE_youvariable (ASPNETCORE - default value).