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Command Line Argument Parser for Rust

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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 -F derive

(See also feature flag reference)

Then 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)
   }
}

Then 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 and reference

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

Documentation:

Re-exports

pub use crate::error::Error;
pub use crate::error::Result;

Modules

_cookbookunstable-doc

Documentation: Cookbook

_deriveunstable-doc

Documentation: Derive Reference

_faqunstable-doc

Documentation: FAQ

_featuresunstable-doc

Documentation: Feature Flags

_tutorialunstable-doc

Documentation: Builder Tutorial

Error reporting

Command line argument parser

Macros

Deprecated, replaced with clap::command!

Create an Arg from a usage string.

commandcargo

Allows you to build the Command instance from your Cargo.toml at compile time.

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>"

Allows you to pull the description from your Cargo.toml at compile time.

Allows you to pull the name from your Cargo.toml at compile time.

Allows you to pull the version from your Cargo.toml at compile time as MAJOR.MINOR.PATCH_PKGVERSION_PRE

Select a ValueParser implementation from the intended type

Structs

Deprecated, replaced with Command

The abstract representation of a command line argument. Used to set all the options and relationships that define a valid argument for the program.

Family of related arguments.

Container for parse results.

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

Deprecated, replaced with ArgMatches::get_many()

A possible value of an argument.

Deprecated, replaced with ArgMatches::get_many()

Enums

Application level settings, which affect how Command operates

Behavior of arguments when they are encountered while parsing

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.

Represents the color preferences for program output

Command line argument parser kind of error

Contains either a regular expression or a set of them or a reference to one.

Provide shell with hint on how to complete an argument.

Origin of the argument’s value

Traits

Parse arguments into enums.

Parse a set of arguments into a user-defined container.

Create a Command relevant for a user-defined container.

Converts an instance of ArgMatches to a user-defined container.

Create a Command relevant for a user-defined container.

Parse command-line arguments into Self.

Parse a sub-command into a user-defined enum.

Parse arguments into enums.

Type Definitions

Build a command-line interface.

Derive Macros

Deprecated, replaced with ValueEnum Generates the ValueEnum impl.