# Getting Started
The simplest way to get started is to install the crate using all features.
```bash
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
```rust
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.