Crate clap

Command Line Argument Parser for Rust

Quick Links:

• Derive [tutorial][_derive::_tutorial] and [reference][_derive]
• Builder [tutorial][_tutorial] and reference
• [Cookbook][_cookbook]
• [FAQ][_faq]
• Discussions

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 1.60.0)

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.

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(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 {}!", 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 information
  -V, --version        Print version information

$ 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]

Related Projects

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

• 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

Re-exports

• pub use crate::builder::ArgAction;
• pub use crate::builder::Command;
• pub use crate::builder::ValueHint;
• pub use crate::builder::Arg;
• pub use crate::builder::ArgGroup;
• pub use crate::parser::ArgMatches;

Modules

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

Macros

• arg
  Create an Arg from a usage string.
• command
  Requires cargo feature flag to be enabled.
• value_parser
  Select a ValueParser implementation from the intended type

Structs

• Id
  Arg or ArgGroup identifier

Enums

• ColorChoice
  Represents the color preferences for program output

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