std::macros::builtin::option_env![src]
macro_rules! option_env( ($name:expr) => ({ /* compiler built-in */ }) )
Optionally inspect 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.
A compile time error is never emitted when using this macro regardless of whether the environment variable is present or not.
Example
fn main() { let key: Option<&'static str> = option_env!("SECRET_KEY"); println!("the secret key might be: {}", key); }let key: Option<&'static str> = option_env!("SECRET_KEY"); println!("the secret key might be: {}", key);