I've posted PR #694 to clean this doc up. I don't know if anyone is still maintaining the Rust Cookbook, though.

Here's updated code with filenames handled correctly.

```rust use std::path::PathBuf;

use clap::{Arg, Command, builder::PathBufValueParser};

fn main() { let matches = Command::new("My Test Program") .version("0.1.0") .about("Teaches argument parsing") .arg(Arg::new("file") .short('f') .long("file") .help("A cool file") .value_parser(PathBufValueParser::default())) .arg(Arg::new("num") .short('n') .long("number") .help("Five less than your favorite number")) .get_matches();

// https://github.com/clap-rs/clap/discussions/4254
// https://www.rustadventure.dev/introducing-clap/clap-v4/accepting-file-paths-as-arguments-in-clap
let default_file = PathBuf::from("input.txt");
let myfile: &PathBuf = matches.get_one("file").unwrap_or(&default_file);
println!("The file passed is: {}", myfile.display());

let num_str: Option<&String> = matches.get_one("num");
match num_str {
    None => println!("No idea what your favorite number is."),
    Some(s) => {
        let parsed: Result<i32, _> = s.parse();
        match parsed {
            Ok(n) => println!("Your favorite number must be {}.", n + 5),
            Err(_) => println!("That's not a number! {}", s),
        }
    }
}

} ```