There is no "built-in" command line parser in Rust. All it has is std::env::args (https://doc.rust-lang.org/std/env/fn.args.html) and std::env::args_os (https://doc.rust-lang.org/std/env/fn.args_os.html), which give you the raw command line. Rust does not follow the "batteries included" philosophy for its base standard library, to avoid "leaking batteries" problems like seen for instance with Python (https://news.ycombinator.com/item?id=19948642).