Module clap::_tutorial::chapter_0

source ·
Available on crate feature unstable-doc only.
Expand description

§Quick Start

You can create an application with several arguments using usage strings.

First, ensure clap is available:

$ cargo add clap
use std::path::PathBuf;

use clap::{arg, command, value_parser, ArgAction, Command};

fn main() {
    let matches = command!() // requires `cargo` feature
        .arg(arg!([name] "Optional name to operate on"))
                -c --config <FILE> "Sets a custom config file"
            // We don't have syntax yet for optional options, so manually calling `required`
            -d --debug ... "Turn debugging information on"
                .about("does testing things")
                .arg(arg!(-l --list "lists test values").action(ArgAction::SetTrue)),

    // You can check the value provided by positional arguments, or option arguments
    if let Some(name) = matches.get_one::<String>("name") {
        println!("Value for name: {name}");

    if let Some(config_path) = matches.get_one::<PathBuf>("config") {
        println!("Value for config: {}", config_path.display());

    // You can see how many times a particular flag or argument occurred
    // Note, only flags can have multiple occurrences
    match matches
        .expect("Counts are defaulted")
        0 => println!("Debug mode is off"),
        1 => println!("Debug mode is kind of on"),
        2 => println!("Debug mode is on"),
        _ => println!("Don't be crazy"),

    // You can check for the existence of subcommands, and if found use their
    // matches just as you would the top level cmd
    if let Some(matches) = matches.subcommand_matches("test") {
        // "$ myapp test" was run
        if matches.get_flag("list") {
            // "$ myapp test -l" was run
            println!("Printing testing lists...");
        } else {
            println!("Not printing testing lists...");

    // Continued program logic goes here...
$ 01_quick --help
A simple to use, efficient, and full-featured Command Line Argument Parser

Usage: 01_quick[EXE] [OPTIONS] [name] [COMMAND]

  test  does testing things
  help  Print this message or the help of the given subcommand(s)

  [name]  Optional name to operate on

  -c, --config <FILE>  Sets a custom config file
  -d, --debug...       Turn debugging information on
  -h, --help           Print help
  -V, --version        Print version

By default, the program does nothing:

$ 01_quick
Debug mode is off

But you can mix and match the various features

$ 01_quick -dd test
Debug mode is on
Not printing testing lists...

See also