# 1.0.0[−][src]Macro core::env

    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.

# 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:

ⓘThis example deliberately fails to compile

    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?!

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