Environment Variable Configuration Provider

These features are only available if the env feature is activated

The EnvironmentVariablesConfigurationProvider loads configuration from environment variable key-value pairs.

The : separator doesn't work with environment variable hierarchical keys on all platforms. __, the double underscore, is:

• Supported by all platforms; for example, the : separator is not supported by Bash, but __ is.
• Automatically replaced by a :

export MyKey="My key from Environment"
export Position__Title=Console
export Position__Name="John Doe"

Call add_env_vars to add environment variables or add_env_vars_with_prefix with a string to specify a prefix for environment variables:

use config::{*, ext::*};

fn main() {
    let config = DefaultConfigurationBuilder::new()
            .add_env_vars_with_prefix("MyCustomPrefix_")
            .build()
            .unwrap();
    
    for (key, value) in config.iter(None) {
        println!("{} = {}", key, value.as_str());
    }
}

Environment variables set with the MyCustomPrefix_ prefix override the default configuration providers. This includes environment variables without the prefix. The prefix is stripped off when the configuration key-value pairs are read.

export MyCustomPrefix_MyKey="My key with MyCustomPrefix_ Environment"
export MyCustomPrefix_Position__Title="Custom Editor"
export MyCustomPrefix_Position__Name="Jane Doe"

Naming of Environment Variables

Environment variable names reflect the structure of an appsettings.json file. Each element in the hierarchy is separated by a double underscore. When the element structure includes an array, the array index should be treated as an additional element name in this path. Consider the following appsettings.json file and its equivalent values represented as environment variables.

{
    "SmtpServer": "smtp.example.com",
    "Logging":
    [
        {
            "Name": "ToEmail",
            "Level": "Critical",
            "Args":
            {
                "FromAddress": "MySystem@example.com",
                "ToAddress": "SRE@example.com"
            }
        },
        {
            "Name": "ToConsole",
            "Level": "Information"
        }
    ]
}

export SmtpServer=smtp.example.com
export Logging__0__Name=ToEmail
export Logging__0__Level=Critical
export Logging__0__Args__FromAddress=MySystem@example.com
export Logging__0__Args__ToAddress=SRE@example.com
export Logging__1__Name=ToConsole
export Logging__1__Level=Information