core::env - Rust
Description: API documentation for the Rust `env` macro in crate `core`.
Keywords: rust, rustlang, rust-lang, env

# 1.0.0[−][src]Macro core::env

    macro_rules! env {
        ($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.

# Examples

    let path: &'static str = env!("PATH");
    println!("the $PATH variable at the time of compiling was: {}", path);

Run

You can customize the error message by passing a string as the second parameter:

ⓘ

    let doc: &'static str = env!("documentation", "what's that?!");

Run

If the `documentation` environment variable is not defined, you'll get the following error:

    error: what's that?!