Crate clap

Expand description

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 1.56.1)

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)]
#[clap(author, version, about, long_about = None)]
struct Args {
   /// Name of the person to greet
   #[clap(short, long, value_parser)]
   name: String,

   /// Number of times to greet
   #[clap(short, long, value_parser, 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
clap [..]
A simple to use, efficient, and full-featured Command Line Argument Parser

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

OPTIONS:
    -c, --count <COUNT>    Number of times to greet [default: 1]
    -h, --help             Print help information
    -n, --name <NAME>      Name of the person to greet
    -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]

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

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::error::Error;

pub use crate::error::Result;

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

App

Deprecated, replaced with Command

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.

Indices

Iterate over indices for where an argument appeared when parsing, via ArgMatches::indices_of

OsValues

Deprecated, replaced with ArgMatches::get_many()

PossibleValue

A possible value of an argument.

Values

Deprecated, replaced with ArgMatches::get_many()

Enums

AppSettings

Application level settings, which affect how Command operates

ArgAction

Behavior of arguments when they are encountered while parsing

ArgSettings

Various settings that apply to arguments and may be set, unset, and checked via getter/setter methods Arg::setting, Arg::unset_setting, and Arg::is_set. This is what the Arg methods which accept a bool use internally.

ColorChoice

Represents the color preferences for program output

ErrorKind

Command line argument parser kind of error

ValueHint

Provide shell with hint on how to complete an argument.

ValueSource

Origin of the argument’s value