# clap > **Command Line Argument Parser for Rust** [](https://crates.io/crates/clap) [](https://crates.io/crates/clap) [](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/LICENSE-APACHE) [](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/LICENSE-MIT) [](https://github.com/clap-rs/clap/actions/workflows/ci.yml?query=branch%3Astaging) [](https://coveralls.io/github/clap-rs/clap?branch=master) [](https://github.com/clap-rs/clap/graphs/contributors) Dual-licensed under [Apache 2.0](LICENSE-APACHE) or [MIT](LICENSE-MIT). 1. [About](#about) 2. Tutorial: [Builder API](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/examples/tutorial_builder/README.md), [Derive API](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/examples/tutorial_derive/README.md) 3. [Examples](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/examples/README.md) 4. [API Reference](https://docs.rs/clap) - [Derive Reference](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/examples/derive_ref/README.md) - [Feature Flags](#feature-flags) 5. [CHANGELOG](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/docs/CHANGELOG.md) 6. [FAQ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/docs/FAQ.md) 7. [Questions & Discussions](https://github.com/clap-rs/clap/discussions) 8. [Contributing](https://github.com/clap-rs/clap/blob/v3.0.0-rc.0/CONTRIBUTING.md) 8. [Sponsors](#sponsors) ## About Create your command-line parser, with all of the bells and whistles, declaratively or procedurally. ### Example ```rust,no_run use clap::Parser; /// Simple program to greet a person #[derive(Parser, Debug)] #[clap(about, version, author)] struct Args { /// Name of the person to greet #[clap(short, long)] name: String, /// Number of times to greet #[clap(short, long, default_value_t = 1)] count: u8, } fn main() { let args = Args::parse(); for _ in 0..args.count { println!("Hello {}!", args.name) } } ``` *(note: requires feature `derive`)* ```bash $ demo --help clap [..] A simple to use, efficient, and full-featured Command Line Argument Parser USAGE: demo[EXE] [OPTIONS] --name OPTIONS: -c, --count Number of times to greet [default: 1] -h, --help Print help information -n, --name Name of the person to greet -V, --version Print version information ``` *(version number and `.exe` extension on windows replaced by placeholders)* ### 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](https://github.com/clap-rs/clap/tree/master/clap_generate), 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](https://github.com/rust-cli/team/) 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 1.54.0) 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](https://github.com/rust-cli/argparse-benchmarks-rs) for CLI parsers optimized for other use cases. ### Related Projects - [clap-verbosity-flag](https://github.com/rust-cli/clap-verbosity-flag) - [clap-cargo](https://github.com/crate-ci/clap-cargo) - [concolor-clap](https://github.com/rust-cli/concolor/tree/main/crates/clap) - [Command-line Apps for Rust](https://rust-cli.github.io/book/index.html) book - [`trycmd`](https://github.com/epage/trycmd): Snapshot testing - Or for more control, [`assert_cmd`](https://github.com/assert-rs/assert_cmd) and [`assert_fs`](https://github.com/assert-rs/assert_fs) ## Feature Flags ### Default Features * **std**: _Not Currently Used._ Placeholder for supporting `no_std` environments in a backwards compatible manner. * **color**: Turns on colored error messages. * **suggestions**: Turns on the `Did you mean '--myoption'?` feature for when users make typos. #### Optional features * **derive**: Enables the custom derive (i.e. `#[derive(Parser)]`). Without this you must use one of the other methods of creating a `clap` CLI listed above. * **cargo**: Turns on macros that read values from `CARGO_*` environment variables. * **env**: Turns on the usage of environment variables during parsing. * **regex**: Enables regex validators. * **unicode**: Turns on support for unicode characters (including emoji) in arguments and help messages. * **wrap_help**: Turns on the help text wrapping feature, based on the terminal size. #### Experimental features **Warning:** These may contain breaking changes between minor releases. * **unstable-replace**: Enable [`App::replace`](https://github.com/clap-rs/clap/issues/2836) * **unstable-multicall**: Enable [`AppSettings::Multicall`](https://github.com/clap-rs/clap/issues/2861) * **unstable-grouped**: Enable [`ArgMatches::grouped_values_of`](https://github.com/clap-rs/clap/issues/2924) ## Sponsors ### Gold [](https://opencollective.com/clap) ### Silver [](https://opencollective.com/clap) ### Bronze [](https://opencollective.com/clap) ### Backer [](https://opencollective.com/clap)