Rendering documentation for your CLI apps

Documentation for CLIs usually consists of a --help section in the command and a manual (man) page.

Both can be automatically generated when using clap, via clap_mangen crate.

pub struct Head {
    /// file to load
    pub file: PathBuf,
    /// how many lines to print
    #[arg(short = "n", default_value = "5")]
    pub count: usize,

Secondly, you need to use a to generate the manual file at compile time from the definition of your app in code.

There are a few things to keep in mind (such as how you want to package your binary) but for now we simply put the man file next to our src folder.

use clap::CommandFactory;

mod cli;

fn main() -> std::io::Result<()> {
    let out_dir = std::path::PathBuf::from(std::env::var_os("OUT_DIR").ok_or_else(|| std::io::ErrorKind::NotFound)?);
    let cmd = cli::Head::command();

    let man = clap_mangen::Man::new(cmd);
    let mut buffer: Vec<u8> = Default::default();
    man.render(&mut buffer)?;

    std::fs::write(out_dir.join("head.1"), buffer)?;


When you now compile your application there will be a head.1 file in your project directory.

If you open that in man you’ll be able to admire your free documentation.