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clap

Command Line Argument Parser for Rust

Dual-licensed under Apache 2.0 or MIT.

About
Tutorial: Builder API, Derive API
Examples
API Reference
- Derive Reference
- Feature Flags
CHANGELOG
FAQ
Questions & Discussions
Contributing
Sponsors

About

Create your command-line parser, with all of the bells and whistles, declaratively or procedurally.

Example

This uses our Derive API which provides access to the Builder API as attributes on a struct:

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)
    }
}

Add this to Cargo.toml:

[dependencies]
clap = { version = "3.2.8", features = ["derive"] }

$ demo --help
clap [..]
Simple program to greet a person

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

(version number and .exe extension on windows replaced by placeholders)

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.

Selecting an API

Why use the declarative Derive API:

Easier to read, write, and modify
Easier to keep the argument declaration and reading of argument in sync
Easier to reuse, e.g. clap-verbosity-flag

Why use the procedural Builder API:

Faster compile times if you aren’t already using other procedural macros
More flexible, e.g. you can look up how many times an argument showed up, what its values were, and what were the indexes of those values. The Derive API can only report presence, number of occurrences, or values but no indices or combinations of data.

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_lex for a lighter-weight, battle-tested CLI parser
clap_mangen for generating man page source (roff)
clap_complete for shell completion support
clap-verbosity-flag
clap-cargo
concolor-clap
Command-line Apps for Rust book
trycmd: Snapshot testing
- Or for more control, assert_cmd and assert_fs

Feature Flags

Default Features

std: Not Currently Used. Placeholder for supporting no_std environments in a backwards compatible manner.
color: Turns on colored error messages.
suggestions: Turns on the Did you mean '--myoption'? feature for when users make typos.

Optional features

deprecated: Guided experience to prepare for next breaking release (at different stages of development, this may become default)
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.
cargo: Turns on macros that read values from CARGO_* environment variables.
env: Turns on the usage of environment variables during parsing.
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.

Experimental features

Warning: These may contain breaking changes between minor releases.

unstable-replace: Enable Command::replace
unstable-grouped: Enable ArgMatches::grouped_values_of
unstable-v4: Preview features which will be stable on the v4.0 release

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