macro_rules! env { ($name:expr) => { ... }; ($name:expr,) => { ... }; }
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
.
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.
let path: &'static str = env!("PATH"); println!("the $PATH variable at the time of compiling was: {}", path);
You can customize the error message by passing a string as the second parameter:
let doc: &'static str = env!("documentation", "what's that?!");
If the documentation
environment variable is not defined, you'll get the following error:
error: what's that?!
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/macro.env.html