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# clap
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> **Command Line Argument Parser for Rust**
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[![Crates.io ](https://img.shields.io/crates/v/clap?style=flat-square )](https://crates.io/crates/clap)
[![Crates.io ](https://img.shields.io/crates/d/clap?style=flat-square )](https://crates.io/crates/clap)
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[![License ](https://img.shields.io/badge/license-Apache%202.0-blue?style=flat-square )](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/LICENSE-APACHE)
[![License ](https://img.shields.io/badge/license-MIT-blue?style=flat-square )](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/LICENSE-MIT)
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[![Build Status ](https://img.shields.io/github/workflow/status/clap-rs/clap/CI/staging?style=flat-square )](https://github.com/clap-rs/clap/actions/workflows/ci.yml?query=branch%3Astaging)
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[![Coverage Status ](https://img.shields.io/coveralls/github/clap-rs/clap/master?style=flat-square )](https://coveralls.io/github/clap-rs/clap?branch=master)
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[![Contributors ](https://img.shields.io/github/contributors/clap-rs/clap?style=flat-square )](https://github.com/clap-rs/clap/graphs/contributors)
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Dual-licensed under [Apache 2.0 ](LICENSE-APACHE ) or [MIT ](LICENSE-MIT ).
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1. [About ](#about )
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2. Tutorial: [Builder API ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/examples/tutorial_builder/README.md ), [Derive API ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/examples/tutorial_derive/README.md )
3. [Examples ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/examples/README.md )
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4. [API Reference ](https://docs.rs/clap )
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- [Derive Reference ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/examples/derive_ref/README.md )
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- [Feature Flags ](#feature-flags )
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5. [CHANGELOG ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/docs/CHANGELOG.md )
6. [FAQ ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/docs/FAQ.md )
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7. [Questions & Discussions ](https://github.com/clap-rs/clap/discussions )
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8. [Contributing ](https://github.com/clap-rs/clap/blob/v3.0.0-rc.1/CONTRIBUTING.md )
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8. [Sponsors ](#sponsors )
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## About
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Create your command-line parser, with all of the bells and whistles, declaratively or procedurally.
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### Example
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<!-- Copied from examples/demo.{rs,md} -->
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```rust,no_run
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use clap::Parser;
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/// 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,
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}
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fn main() {
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let args = Args::parse();
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for _ in 0..args.count {
println!("Hello {}!", args.name)
}
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}
```
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*(note: requires feature `derive` )*
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```bash
$ demo --help
clap [..]
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A simple to use, efficient, and full-featured Command Line Argument Parser
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USAGE:
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demo[EXE] [OPTIONS] --name < NAME >
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OPTIONS:
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-c, --count < COUNT > Number of times to greet [default: 1]
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-h, --help Print help information
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-n, --name < NAME > Name of the person to greet
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-V, --version Print version information
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```
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*(version number and `.exe` extension on windows replaced by placeholders)*
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### Aspirations
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- 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
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- 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
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- We follow semver and will wait about 6-9 months between major breaking changes
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- We will support the last two minor Rust releases (MSRV, currently 1.54.0)
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While these aspirations can be at odds with fast build times and low binary
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size, we will still strive to keep these reasonable for the flexibility you
get. Check out the
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[argparse-benchmarks ](https://github.com/rust-cli/argparse-benchmarks-rs ) for
CLI parsers optimized for other use cases.
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### Related Projects
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- [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 )
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- [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 )
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## Feature Flags
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### Default Features
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* **std**: _Not Currently Used._ Placeholder for supporting `no_std` environments in a backwards compatible manner.
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* **color**: Turns on colored error messages.
* **suggestions**: Turns on the `Did you mean '--myoption'?` feature for when users make typos.
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#### Optional features
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* **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.
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* **cargo**: Turns on macros that read values from `CARGO_*` environment variables.
* **env**: Turns on the usage of environment variables during parsing.
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* **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.
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#### Experimental features
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**Warning:** These may contain breaking changes between minor releases.
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* **unstable-replace**: Enable [`App::replace` ](https://github.com/clap-rs/clap/issues/2836 )
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* **unstable-multicall**: Enable [`AppSettings::Multicall` ](https://github.com/clap-rs/clap/issues/2861 )
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* **unstable-grouped**: Enable [`ArgMatches::grouped_values_of` ](https://github.com/clap-rs/clap/issues/2924 )
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## Sponsors
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### Gold
[![ ](https://opencollective.com/clap/tiers/gold.svg?avatarHeight=36&width=600 )](https://opencollective.com/clap)
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### Silver
[![ ](https://opencollective.com/clap/tiers/silver.svg?avatarHeight=36&width=600 )](https://opencollective.com/clap)
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### Bronze
[![ ](https://opencollective.com/clap/tiers/bronze.svg?avatarHeight=36&width=600 )](https://opencollective.com/clap)
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### Backer
[![ ](https://opencollective.com/clap/tiers/backer.svg?avatarHeight=36&width=600 )](https://opencollective.com/clap)