Getting Started

The simplest way to get started is to install the crate using all features.

cargo add more-config --features all

Once you know which configuration sources you want to support, you can limit the features to only the ones you need.

Example

Configuration is a common requirement of virtually any application and can be performed using one or more configuration providers. Configuration providers read configuration data from key-value pairs using a variety of configuration sources:

• Settings files, such as appsettings.json
• Environment variables
• Command-line arguments
• In-memory data structures
• Custom providers

use config::prelude::*;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error + 'static>> {
    let config = config::builder()
        .add_in_memory(&[("MyKey", "MyValue")])
        .add_json_file("appsettings.json".is().optional())
        .add_env_vars()
        .add_command_line()
        .build()?;

    println!("MyKey = {}", config.get("MyKey").unwrap().as_str());
    Ok(())
}

Configuration providers that are added later have higher precedence and override previous key settings. For example, if MyKey is set in both appsettings.json and an environment variable, then the environment variable value is used. If appsettings.json does not exist or contain MyKey and there is no environment variable for MyKey, then the in-memory value of MyValue is used. Finally, if command-line argument --MyKey is provided, it overrides all other values.