Some popular applications, such as cargo and docker, use subcommands to provide multiple commands inside a single binary. We can also support subcommands with the clap crate. A microservice might have two commands: one to run the server and one to generate a secret for the HTTP cookies. Take a look at the following code:

let matches = App::new("Server with keys")
    .setting(AppSettings::SubcommandRequiredElseHelp)
    .subcommand(SubCommand::with_name("run")
        .about("run the server")
        .arg(Arg::with_name("address")
            .short("a")
            .long("address")
            .takes_value(true)
            .help("address of the server"))
    .subcommand(SubCommand::with_name("key")
        .about("generates a secret key for cookies")))
    .get_matches();

Here, we have used two methods. The setting method tweaks the builder and you can set it with variants of the AppSettings enumeration. The SubcommandRequiredElseHelp method requires us to use subcommands or prints help message if no subcommands are provided. To add a subcommand, we use the subcommand method with the SubCommand instance that we created with the with_name method. A subcommand instance also has methods to set meta information about a subcommand, like we did with the App instance. Subcommands can also take arguments.

In the preceding example above, we added two subcommands—run, to run the server, and key, to generate secrets. You can use these when you start the application:

$ cargo run -- run --address 0.0.0.0:2345

We have two run arguments because the cargo has a command with the same name.