Function temp_env::with_var

pub fn with_var<K, V, F>(key: K, value: Option<V>, closure: F) where
    K: AsRef<OsStr> + Clone + Eq + Hash,
    V: AsRef<OsStr> + Clone,
    F: Fn() + UnwindSafe + RefUnwindSafe, 

Sets a single environment variable for the duration of the closure.

The previous values are restored when the closure completes or panics, before unwinding the panic.

If value is set to None, then the environment variable is unset.