macro_rules! option_env {
    ($name:expr $(,)?) => { ... };
}
Available on non-crate feature miri-test-libstd only.
Expand description

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. Use std::env::var instead if you want to read the value at runtime.

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:?}");