Macro rerun_if_env_changed

macro_rules! rerun_if_env_changed {
    (to: $stream:expr, $($key:expr),+ $(,)?) => { ... };
    ($($key:expr),+ $(,)?) => { ... };
}

Tells Cargo to run again if the file or directory at $key changes.

This is equivalent to:

println!("cargo:rerun-if-env-changed=$key");

$key is the name of an environment variable which indicates that if the environment variable’s value changes the build script should be rerun. This basically behaves the same as rerun_if_changed! except that it works with environment variables instead. Note that the environment variables here are intended for global environment variables like CC and such, it’s not necessary to use this for env vars like TARGET that Cargo sets. Also note that if rerun_if_env_changed! is used then Cargo will only rerun the build script if those environment variables change or if files printed out by rerun_if_changed! change.

Examples

This is useful for tracking build-dependent files that Cargo does not already know.

cargo_emit::rerun_if_env_changed!("MY_DEPENDENCY", "PATH");

or, in case you want it to emit to a custom stream:

let mut stdout = std::io::stdout();
cargo_emit::rerun_if_env_changed!(
    to: stdout,
    "MY_DEPENDENCY", "PATH"
);