Macro err

macro_rules! err {
    ($status:expr, $fmt:expr) => { ... };
    ($status:expr, $fmt:expr, $($args:tt)*) => { ... };
}

Prints the formatted message to the standard error output (stderr) and terminates the program with the given status value. The program name, a colon, and a space are output before the message, and a newline character follows.