clap

Command Line Argument Parser for Rust

Dual-licensed under Apache 2.0 or MIT.

1. About
2. Tutorial: Builder API, Derive API
3. Examples
4. API Reference
   • Derive Reference
   • Feature Flags
5. CHANGELOG
6. FAQ
7. Questions & Discussions
8. Contributing

About

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

Example

use clap::Parser;

#[derive(Parser)]
#[clap(about, version, author)] // Pull these from `Cargo.toml`
struct Cli {
    /// Sets a custom config file. Could have been an Option<T> with no default too
    #[clap(short, long, default_value = "default.toml", value_name = "PATH")]
    config: std::path::PathBuf,
    /// Some input. Because this isn't an Option<T> it's required to be used
    input: String,
    /// A level of verbosity, and can be used multiple times
    #[clap(short, long, parse(from_occurrences))]
    verbose: i32,
}

fn main() {
    let args = Cli::parse();

    println!("Value for config: {}", args.config.display());
    println!("Using input file: {}", args.input);

    // Vary the output based on how many times the user used the "verbose" flag
    // (i.e. 'myprog -v -v -v' or 'myprog -vvv' vs 'myprog -v'
    match args.verbose {
        0 => println!("No verbose info"),
        1 => println!("Some verbose info"),
        2 => println!("Tons of verbose info"),
        _ => println!("Don't be ridiculous"),
    }

    // more program logic goes here...
}

$ demo --help
clap [..]

A simple to use, efficient, and full-featured Command Line Argument Parser

USAGE:
    demo[EXE] [OPTIONS] <INPUT>

ARGS:
    <INPUT>    Some input. Because this isn't an Option<T> it's required to be used

OPTIONS:
    -c, --config <PATH>    Sets a custom config file. Could have been an Option<T> with no default
                           too [default: default.toml]
    -h, --help             Print help information
    -v, --verbose          A level of verbosity, and can be used multiple times
    -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 months between major breaking changes
• We will support the last two minor Rust releases (MSRV)

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.

Related Projects

• 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

• 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 App::replace
• unstable-multicall: Enable AppSettings::Multicall
• unstable-grouped: Enable ArgMatches::grouped_values_of