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

clio for reading/writing to files specified as arguments
clap-verbosity-flag
clap-cargo
concolor-clap

Testing

trycmd: Bulk snapshot testing
snapbox: Specialized snapshot testing
assert_cmd and assert_fs: Customized testing

Documentation:

Command-line Apps for Rust book

Modules§

builder: Define Command line arguments
error: Error reporting
parser: Command line argument parser

Macros§

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

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§

Args: Parse a set of arguments into a user-defined container.
CommandFactory: Create a Command relevant for a user-defined container.
FromArgMatches: Converts an instance of ArgMatches to a user-defined container.
Parser: Parse command-line arguments into Self.
Subcommand: Parse a sub-command into a user-defined enum.
ValueEnum: Parse arguments into enums.

Type Aliases§

Error: Command Line Argument Parser Error

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