Macro option_env

macro_rules! option_env {
    ($name:expr $(,)?) => { ... };
}

Available on crate feature std only.

Optionally inspects an environment variable at compile time.

If the named environment variable is present at compile time, this will expand into an expression of type Option<&'static str> whose value is Some of the value of the environment variable (a compilation error will be emitted if the environment variable is not a valid Unicode string). If the environment variable is not present, then this will expand to None. See Option<T> for more information on this type. Use std::env::var instead if you want to read the value at runtime.

A compile time error is only emitted when using this macro if the environment variable exists and is not a valid Unicode string. To also emit a compile error if the environment variable is not present, use the env! macro instead.

Examples

let key: Option<&'static str> = option_env!("SECRET_KEY");
println!("the secret key might be: {key:?}");