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

# 1.0.0[−][src]Macro std::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?!

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g., `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g., `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)