Macro core::option_env

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

This is supported on non-crate feature miri-test-libstd or test or doctest 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. If the environment variable is not present, then this will expand to None. See Option<T> for more information on this type.

A compile time error is never emitted when using this macro regardless of whether the environment variable is present or not.

Examples

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