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Environment variable prefixes

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Hierarchical data is represented using : as the level delimiter. However, for environmental variables, the : character is normalized to __, because the latter is supported on all platforms. This change affects how normalized and non-normalized prefixes and keys are compared. Specifically, you can now add environment variables by specifying a prefix containing either : or __ as the delimiter. Either syntax will match any environment variables with a matching prefix followed by either a : or __. Some environment variables that theoretically didn't match the filter previously may now match the filter.

Version introduced

.NET 7 Preview 4

Previous behavior

Previously, the following code printed False:

using Microsoft.Extensions.Configuration;

const string myValue = "value1";
Environment.SetEnvironmentVariable("MY_PREFIX__ConfigKey", myValue);

IConfiguration config = new ConfigurationBuilder()
    .AddEnvironmentVariables(prefix: "MY_PREFIX__")
    .Build();

var loadedValue = config.GetValue<string?>("ConfigKey", null);

Console.WriteLine(String.Equals(myValue, loadedValue));
// False

In order for the MY_PREFIX__ConfigKey environment variable to be added to the configuration, you had to add environment variables using a delimiter of : instead of __:

using Microsoft.Extensions.Configuration;

const string myValue = "value1";
Environment.SetEnvironmentVariable("MY_PREFIX__ConfigKey", myValue);

IConfiguration config = new ConfigurationBuilder()
    .AddEnvironmentVariables(prefix: "MY_PREFIX:")
    .Build();

var loadedValue = config.GetValue<string?>("ConfigKey", null);

Console.WriteLine(String.Equals(myValue, loadedValue));
// True

New behavior

Starting in .NET 7, the following code prints True:

using Microsoft.Extensions.Configuration;

const string myValue = "value1";
Environment.SetEnvironmentVariable("MY_PREFIX__ConfigKey", myValue);

IConfiguration config = new ConfigurationBuilder()
    .AddEnvironmentVariables(prefix: "MY_PREFIX__")
    .Build();

var loadedValue = config.GetValue<string?>("ConfigKey", null);

Console.WriteLine(String.Equals(myValue, loadedValue));
// True

Type of breaking change

This change can affect binary compatibility.

Reason for change

This change was made to fix an unintentional behavior change for normalizing environment variable prefix filters in .NET 6. The new behavior matches the .NET 5 behavior.

Most developers won't be affected by this change, since it corrects previously erroneous behavior. In the unlikely case that you relied on the fact that a prefix containing __ didn't match an environment variable containing __, consider changing the prefixes of those variables.

Affected APIs

See also