Module clap::_cookbook::multicall_busybox

Available on crate feature unstable-doc only.

Example: busybox-like CLI (Builder API)

use std::path::PathBuf;
use std::process::exit;

use clap::{value_parser, Arg, ArgAction, Command};

fn applet_commands() -> [Command; 2] {
    [
        Command::new("true").about("does nothing successfully"),
        Command::new("false").about("does nothing unsuccessfully"),
    ]
}

fn main() {
    let cmd = Command::new(env!("CARGO_CRATE_NAME"))
        .multicall(true)
        .subcommand(
            Command::new("busybox")
                .arg_required_else_help(true)
                .subcommand_value_name("APPLET")
                .subcommand_help_heading("APPLETS")
                .arg(
                    Arg::new("install")
                        .long("install")
                        .help("Install hardlinks for all subcommands in path")
                        .exclusive(true)
                        .action(ArgAction::Set)
                        .default_missing_value("/usr/local/bin")
                        .value_parser(value_parser!(PathBuf)),
                )
                .subcommands(applet_commands()),
        )
        .subcommands(applet_commands());

    let matches = cmd.get_matches();
    let mut subcommand = matches.subcommand();
    if let Some(("busybox", cmd)) = subcommand {
        if cmd.contains_id("install") {
            unimplemented!("Make hardlinks to the executable here");
        }
        subcommand = cmd.subcommand();
    }
    match subcommand {
        Some(("false", _)) => exit(1),
        Some(("true", _)) => exit(0),
        _ => unreachable!("parser should ensure only valid subcommand names are used"),
    }
}

See the documentation for Command::multicall for rationale.

This example omits every command except true and false, which are the most trivial to implement,

$ busybox true
? 0

$ busybox false
? 1

Note: without the links setup, we can’t demonstrate the multicall behavior

But includes the --install option as an example of why it can be useful for the main program to take arguments that aren’t applet subcommands.

$ busybox --install
? failed
...

Though users must pass something:

$ busybox
? failed
Usage: busybox [OPTIONS] [APPLET]

APPLETS:
  true   does nothing successfully
  false  does nothing unsuccessfully
  help   Print this message or the help of the given subcommand(s)

Options:
      --install <install>  Install hardlinks for all subcommands in path
  -h, --help               Print help