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