clap

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Command Line Argument Parser for Rust

It is a simple-to-use, efficient, and full-featured library for parsing command line arguments and subcommands when writing console/terminal applications.

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Table of Contents

Created by gh-md-toc

What's New

Here's the highlights for v2.10.2

Here's the highlights for v2.10.1

Here's the highlights for v2.10.0

Here's the highlights for v2.9.3

Here's the highlights for v2.9.2

Here's the highlights for v2.9.0

Here's the highlights for v2.8.0

Here's the highlights for v2.7.1

Here's the highlights for v2.7.0

Here's the highlights for v2.6.0

Here's what's new in v.2.5.2

Here's what's new in v.2.5.0

Here's what's new in v2.4.3

Here's the highlights from v2.4.0

Here's the highlights from v2.3.0

Here's the highlights from v2.2.1

An example of the optional colored help:

screenshot

Here's the highlights from v2.2.0

An example of the help text wrapping at term width:

screenshot

In v2.1.2

For full details, see CHANGELOG.md

About

clap is used to parse and validate the string of command line arguments provided by the user at runtime. You provide the list of valid possibilities, and clap handles the rest. This means you focus on your applications functionality, and less on the parsing and validating of arguments.

clap also provides the traditional version and help switches (or flags) 'for free' meaning automatically with no configuration. It does this by checking list of valid possibilities you supplied and adding only the ones you haven't already defined. If you are using subcommands, clap will also auto-generate a help subcommand for you in addition to the traditional flags.

Once clap parses the user provided string of arguments, it returns the matches along with any applicable values. If the user made an error or typo, clap informs them of the mistake and exits gracefully (or returns a Result type and allows you to perform any clean up prior to exit). Because of this, you can make reasonable assumptions in your code about the validity of the arguments.

FAQ

For a full FAQ and more in depth details, see the wiki page

Comparisons

First, let me say that these comparisons are highly subjective, and not meant in a critical or harsh manner. All the argument parsing libraries out there (to include clap) have their own strengths and weaknesses. Sometimes it just comes down to personal taste when all other factors are equal. When in doubt, try them all and pick one that you enjoy :) There's plenty of room in the Rust community for multiple implementations!

How does clap compare to getopts?

getopts is a very basic, fairly minimalist argument parsing library. This isn't a bad thing, sometimes you don't need tons of features, you just want to parse some simple arguments, and have some help text generated for you based on valid arguments you specify. The downside to this approach is that you must manually implement most of the common features (such as checking to display help messages, usage strings, etc.). If you want a highly custom argument parser, and don't mind writing the majority of the functionality yourself, getopts is an excellent base.

getopts also doesn't allocate much, or at all. This gives it a very small performance boost. Although, as you start implementing additional features, that boost quickly disappears.

Personally, I find many, many uses of getopts are manually implementing features that clap provides by default. Using clap simplifies your codebase allowing you to focus on your application, and not argument parsing.

How does clap compare to docopt.rs?

I first want to say I'm a big a fan of BurntSushi's work, the creator of Docopt.rs. I aspire to produce the quality of libraries that this man does! When it comes to comparing these two libraries they are very different. docopt tasks you with writing a help message, and then it parsers that message for you to determine all valid arguments and their use. Some people LOVE this approach, others do not. If you're willing to write a detailed help message, it's nice that you can stick that in your program and have docopt do the rest. On the downside, it's far less flexible.

docopt is also excellent at translating arguments into Rust types automatically. There is even a syntax extension which will do all this for you, if you're willing to use a nightly compiler (use of a stable compiler requires you to somewhat manually translate from arguments to Rust types). To use BurntSushi's words, docopt is also a sort of black box. You get what you get, and it's hard to tweak implementation or customize the experience for your use case.

Because docopt is doing a ton of work to parse your help messages and determine what you were trying to communicate as valid arguments, it's also one of the more heavy weight parsers performance-wise. For most applications this isn't a concern and this isn't to say docopt is slow, in fact from it. This is just something to keep in mind while comparing.

All else being equal, what are some reasons to use clap?

clap is as fast, and as lightweight as possible while still giving all the features you'd expect from a modern argument parser. In fact, for the amount and type of features clap offers it remains about as fast as getopts. If you use clap when just need some simple arguments parsed, you'll find it's a walk in the park. clap also makes it possible to represent extremely complex, and advanced requirements, without too much thought. clap aims to be intuitive, easy to use, and fully capable for wide variety use cases and needs.

Features

Below are a few of the features which clap supports, full descriptions and usage can be found in the documentation and examples/ directory

Quick Example

The following examples show a quick example of some of the very basic functionality of clap. For more advanced usage, such as requirements, conflicts, groups, multiple values and occurrences see the documentation, examples/ directory of this repository or the video tutorials (which are quite outdated by now).

NOTE: All these examples are functionally the same, but show three different styles in which to use clap

The following example is show a method that allows more advanced configuration options (not shown in this small example), or even dynamically generating arguments when desired. The downside is it's more verbose.

```rust // (Full example with detailed comments in examples/01bquickexample.rs) // // This example demonstrates clap's full 'builder pattern' style of creating arguments which is // more verbose, but allows easier editing, and at times more advanced options, or the possibility // to generate arguments dynamically. extern crate clap; use clap::{Arg, App, SubCommand};

fn main() { let matches = App::new("My Super Program") .version("1.0") .author("Kevin K. kbknapp@gmail.com") .about("Does awesome things") .arg(Arg::withname("config") .short("c") .long("config") .valuename("FILE") .help("Sets a custom config file") .takesvalue(true)) .arg(Arg::withname("INPUT") .help("Sets the input file to use") .required(true) .index(1)) .arg(Arg::withname("v") .short("v") .multiple(true) .help("Sets the level of verbosity")) .subcommand(SubCommand::withname("test") .about("controls testing features") .version("1.3") .author("Someone E. someone_else@other.com") .arg(Arg::withname("debug") .short("d") .help("print debug information verbosely"))) .getmatches();

// Gets a value for config if supplied by user, or defaults to "default.conf"
let config = matches.value_of("config").unwrap_or("default.conf");
println!("Value for config: {}", config);

// Calling .unwrap() is safe here because "INPUT" is required (if "INPUT" wasn't
// required we could have used an 'if let' to conditionally get the value)
println!("Using input file: {}", matches.value_of("INPUT").unwrap());

// 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 matches.occurrences_of("v") {
    0 => println!("No verbose info"),
    1 => println!("Some verbose info"),
    2 => println!("Tons of verbose info"),
    3 | _ => println!("Don't be crazy"),
}

// You can handle information about subcommands by requesting their matches by name
// (as below), requesting just the name used, or both at the same time
if let Some(matches) = matches.subcommand_matches("test") {
    if matches.is_present("debug") {
        println!("Printing debug info...");
    } else {
        println!("Printing normally...");
    }
}

// more program logic goes here...

} ```

The following example is functionally the same as the one above, but shows a far less verbose method but sacrifices some of the advanced configuration options (not shown in this small example).

```rust // (Full example with detailed comments in examples/01aquickexample.rs) // // This example demonstrates clap's "usage strings" method of creating arguments which is less // less verbose extern crate clap; use clap::{Arg, App, SubCommand};

fn main() { let matches = App::new("myapp") .version("1.0") .author("Kevin K. kbknapp@gmail.com") .about("Does awesome things") .argsfromusage( "-c, --config=[FILE] 'Sets a custom config file' 'Sets the input file to use' -v... 'Sets the level of verbosity'") .subcommand(SubCommand::withname("test") .about("controls testing features") .version("1.3") .author("Someone E. someone_else@other.com") .argfromusage("-d, --debug 'Print debug information'")) .getmatches();

// Same as previous example...

} ```

This final method shows how you can use a YAML file to build your CLI and keep your Rust source tidy or support multiple localized translations by having different YAML files for each localization. First, create the cli.yml file to hold your CLI options, but it could be called anything we like (we'll use the same both examples above to keep it functionally equivalent):

yaml name: myapp version: 1.0 author: Kevin K. <kbknapp@gmail.com> about: Does awesome things args: - config: short: c long: config value_name: FILE help: Sets a custom config file takes_value: true - INPUT: help: Sets the input file to use required: true index: 1 - verbose: short: v multiple: true help: Sets the level of verbosity subcommands: - test: about: controls testing features version: 1.3 author: Someone E. <someone_else@other.com> args: - debug: short: d help: print debug information

Now we create our main.rs file just like we would have with the previous two examples:

```rust // (Full example with detailed comments in examples/17_yaml.rs) // // This example demonstrates clap's building from YAML style of creating arguments which is far // more clean, but takes a very small performance hit compared to the other two methods.

[macro_use]

extern crate clap; use clap::App;

fn main() { // The YAML file is found relative to the current file, similar to how modules are found let yaml = loadyaml!("cli.yml"); let matches = App::fromyaml(yaml).get_matches();

// Same as previous examples...

} ```

NOTE: The YAML and macro builder options require adding a special features flag when compiling clap because they are not compiled by default. Simply change your clap = "2" to clap = {version = "2", features = ["yaml"]} for YAML, or features = ["unstable"] for the macro builder, in your Cargo.toml.

If you were to compile any of the above programs and run them with the flag --help or -h (or help subcommand, since we defined test as a subcommand) the following would be output

```sh $ myprog --help My Super Program 1.0 Kevin K. kbknapp@gmail.com Does awesome things

USAGE: MyApp [FLAGS] [OPTIONS] [SUBCOMMAND]

FLAGS: -h, --help Prints this message -v Sets the level of verbosity -V, --version Prints version information

OPTIONS: -c, --config Sets a custom config file

ARGS: INPUT The input file to use

SUBCOMMANDS: help Prints this message test Controls testing features ```

NOTE: You could also run myapp test --help to see similar output and options for the test subcommand.

Try it!

Pre-Built Test

To try out the pre-built example, use the following steps:

BYOB (Build Your Own Binary)

To test out clap's default auto-generated help/version follow these steps: * Create a new cargo project $ cargo new fake --bin && cd fake * Add clap to your Cargo.toml * toml [dependencies] clap = "2"

```rust extern crate clap; use clap::App;

fn main() { App::new("fake").version("v1.0-beta").get_matches(); } ```

Usage

For full usage, add clap as a dependency in your Cargo.toml file to use from crates.io:

toml [dependencies] clap = "2" Or track the latest on the master branch at github:

toml [dependencies.clap] git = "https://github.com/kbknapp/clap-rs.git"

Add extern crate clap; to your crate root.

Define a list of valid arguments for your program (see the documentation or examples/ directory of this repo)

Then run cargo build or cargo update && cargo build for your project.

Optional Dependencies / Features

If you'd like to keep your dependency list to only clap, you can disable any features that require an additional dependency. To do this, add this to your Cargo.toml:

toml [dependencies.clap] version = "2" default-features = false

You can also selectively enable only the features you'd like to include, by adding:

```toml [dependencies.clap] version = "2" default-features = false

Cherry-pick the features you'd like to use

features = [ "suggestions", "color" ] `` The following is a list of optionalclap` features:

Dependencies Tree

The following graphic depicts claps dependency graph (generated using cargo-graph).

clap dependencies

More Information

You can find complete documentation on the github-pages site for this project.

You can also find usage examples in the examples/ directory of this repo.

Video Tutorials

There's also the video tutorial series Argument Parsing with Rust.

NOTE: This series is getting out of date and needs to be updated

How to Contribute

Contributions are always welcome! And there is a multitude of ways in which you can help depending on what you like to do, or are good at. Anything from documentation, code cleanup, issue completion, new features, you name it, even filing issues is contributing and greatly appreciated!

Another really great way to help is if you find an interesting, or helpful way in which to use clap. You can either add it to the examples/ directory, or file an issue and tell me. I'm all about giving credit where credit is due :)

Please read CONTRIBUTING.md before you start contributing.

Running the tests

If contributing, you can run the tests as follows (assuming you're in the clap-rs directory)

``` $ cargo test

If your tests affect the YAML feature set

$ cargo test --features yaml

Only on nightly compiler:

$ cargo build --features lints ```

Goals

There are a few goals of clap that I'd like to maintain throughout contributions. If your proposed changes break, or go against any of these goals we'll discuss the changes further before merging (but will not be ignored, all contributes are welcome!). These are by no means hard-and-fast rules, as I'm no expert and break them myself from time to time (even if by mistake or ignorance :P).

License

clap is licensed under the MIT license. Please read the LICENSE-MIT file in this repository for more information.

Recent Breaking Changes

clap follows semantic versioning, so breaking changes should only happen upon major version bumps. The only exception to this rule is breaking changes that happen due to implementation that was deemed to be a bug, security concerns, or it can be reasonably proved to affect no code. For the full details, see CHANGELOG.md.

As of 2.0.0 (From 1.x)

Deprecations

Old method names will be left around for several minor version bumps, or one major version bump.

As of 2.2.0: