Crate clap

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Command Line Argument Parser for Rust

Quick Links:


  • 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 1.64.0)

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.



$ cargo add clap --features derive

(See also feature flag reference)

Then define your CLI in

use clap::Parser;

/// Simple program to greet a person
#[derive(Parser, Debug)]
#[command(author, 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 {}!",

And try it out:

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

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

  -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 and reference

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




Documentation: Cookbook
Documentation: Derive Reference
Documentation: FAQ
Documentation: Feature Flags
Documentation: Builder Tutorial
Error reporting
Command line argument parser


Create an Arg from a usage string.
Allows you to build the Command instance from your Cargo.toml at compile time.
Allows you to pull the authors for the command from your Cargo.toml at compile time in the form: "author1 lastname <>:author2 lastname <>"
Allows you to pull the description from your Cargo.toml at compile time.
Allows you to pull the name from your Cargo.toml at compile time.
Allows you to pull the version from your Cargo.toml at compile time as MAJOR.MINOR.PATCH_PKGVERSION_PRE
Select a ValueParser implementation from the intended type


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


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


Parse a set of arguments into a user-defined container.
Create a Command relevant for a user-defined container.
Converts an instance of ArgMatches to a user-defined container.
Parse command-line arguments into Self.
Parse a sub-command into a user-defined enum.
Parse arguments into enums.

Type Definitions

Command Line Argument Parser Error