macro_rules! env { ($name:expr $(,)?) => { ... }; ($name:expr, $error_msg:expr $(,)?) => { ... }; }
Expand description
Inspects an environment variable at compile time.
This macro will expand to the value of the named environment variable at
compile time, yielding an expression of type &'static str
. Use
std::env::var
instead if you want to read the value at runtime.
If the environment variable is not defined, then a compilation error
will be emitted. To not emit a compile error, use the option_env!
macro instead.
§Examples
let path: &'static str = env!("PATH");
println!("the $PATH variable at the time of compiling was: {path}");
RunYou can customize the error message by passing a string as the second parameter:
If the documentation
environment variable is not defined, you’ll get
the following error:
error: what's that?!