Crate clap

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Command Line Argument Parser for Rust

Quick Links:

  • Derive [tutorial][_derive::_tutorial::chapter_0] and [reference][_derive]
  • Builder [tutorial][_tutorial::chapter_0] and reference
  • [Cookbook][_cookbook]
  • [FAQ][_faq]
  • Discussions
  • CHANGELOG (includes major version migration guides)

§Aspirations

  • Out of the box, users get a polished CLI experience
    • Including common argument behavior, help generation, suggested fixes for users, colored output, shell completions, etc
  • Flexible enough to port your existing CLI interface
    • However, we won’t necessarily streamline support for each use case
  • Reasonable parse performance
  • Resilient maintainership, including
    • Willing to break compatibility rather than batching up breaking changes in large releases
    • Leverage feature flags to keep to one active branch
    • Being under WG-CLI to increase the bus factor
  • We follow semver and will wait about 6-9 months between major breaking changes
  • We will support the last two minor Rust releases (MSRV, currently 1.74)

While these aspirations can be at odds with fast build times and low binary size, we will still strive to keep these reasonable for the flexibility you get. Check out the argparse-benchmarks for CLI parsers optimized for other use cases.

§Example

Run

$ cargo add clap --features derive

(See also [feature flag reference][_features])

Then define your CLI in main.rs:

use clap::Parser;

/// Simple program to greet a person
#[derive(Parser, Debug)]
#[command(version, about, long_about = None)]
struct Args {
    /// Name of the person to greet
    #[arg(short, long)]
    name: String,

    /// Number of times to greet
    #[arg(short, long, default_value_t = 1)]
    count: u8,
}

fn main() {
    let args = Args::parse();

    for _ in 0..args.count {
        println!("Hello {}!", args.name);
    }
}

And try it out:

$ demo --help
A simple to use, efficient, and full-featured Command Line Argument Parser

Usage: demo[EXE] [OPTIONS] --name <NAME>

Options:
  -n, --name <NAME>    Name of the person to greet
  -c, --count <COUNT>  Number of times to greet [default: 1]
  -h, --help           Print help
  -V, --version        Print version

$ demo --name Me
Hello Me!

(version number and .exe extension on windows replaced by placeholders)

See also the derive [tutorial][_derive::_tutorial] and [reference][_derive]

Augment clap:

  • wild for supporting wildcards (*) on Windows like you do Linux
  • argfile for loading additional arguments from a file (aka response files)
  • shadow-rs for generating Command::long_version
  • clap_mangen for generating man page source (roff)
  • clap_complete for shell completion support

CLI Helpers

Testing

Documentation:

Modules§

Macros§

Structs§

  • Arg
    The abstract representation of a command line argument. Used to set all the options and relationships that define a valid argument for the program.
  • ArgGroup
    Family of related arguments.
  • ArgMatches
    Container for parse results.
  • Command
    Build a command-line interface.
  • Id
    Arg or ArgGroup identifier

Enums§

  • ArgAction
    Behavior of arguments when they are encountered while parsing
  • ColorChoice
    Represents the color preferences for program output
  • ValueHint
    Provide shell with hint on how to complete an argument.

Traits§

Type Aliases§

  • Error
    Command Line Argument Parser Error