envhead/README.md

# Envhead

Envhead is a crate that creates environment variable names using a static prefix.

## Setup
First, you should define the prefix by setting the `ENV_HEAD_PREFIX` environment variable to the desired value. When the `ENV_HEAD_PREFIX` variable is not defined, `ENV` is used as the default prefix. In the following examples, we will use `MY_APP` as the prefix.

In case you are working with macOS or Linux, you might use Bash like this:

```bash
ENV_HEAD_PREFIX=MY_APP cargo build
```

Using an IDE from JetBrains like [RustRover](https://www.jetbrains.com/rust/), you can set the environment variable in the [run configuration](https://www.jetbrains.com/help/rust/cargo-run-debug-configuration.html) and for your [integrated terminal](https://www.jetbrains.com/help/clion/settings-tools-terminal.html).

Do you use a CI/CD pipeline? You can set the environment variable in your pipeline configuration. Do you build your application in a Docker container? You can set the environment variable in your Dockerfile as well.

**Please notice:** This setup procedure is required just for the development environment. Your compiled program(s) will not depend on the `ENV_HEAD_PREFIX` environment variable.

## Usage
Now, in your code, you can use the `envhead!` macro to create environment variable names.

```rust
use envhead::envhead;

fn main() {
    let env_var = envhead!("server_port");

    // Prints "MY_APP_SERVER_PORT":
    println!("{}", env_var);
}
```

You might find it useful to use `envhead` together with `clap` to create environment variable names for your command line arguments:

```rust
use clap::Args;
use envhead::envhead;

#[derive(Debug, Args)]
pub struct ServerArgs {
    #[arg(
        short = 'p', long,
        required = false,
        value_name = "port",
        value_hint = clap::ValueHint::Other,
        help = "The server's port.",
        default_value_t = 8000,
        env = envhead!("server_port"),
    )]
    pub port: u16,

    #[arg(
        long,
        required = true,
        value_name = "SECRET_TOKEN",
        value_hint = clap::ValueHint::Other,
        help = "The secret token to authenticate the client.",
        env = envhead!("server_secret_token"),
    )]
    pub secret_token: Option<String>,
}
```

# Changelog

### Version 1.0.0
- Initial release