Crate clap [−] [src]

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, or terminal applications.

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 if you haven't them already (or only defined some of them), clap will auto- generate the applicable ones. 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. 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. When using getopts 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 most the argument parser yourself, getopts is an excellent base.

Due to it's lack of features, getopts also doesn't allocate much, or at all. This gives it somewhat of a performance boost. Although, as you start implementing those features you need manually, that boost quickly disappears.

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

Reasons to use getopts instead of clap

You need a few allocations as possible, don't plan on implementing any additional features
You want a highly custom argument parser, but want to use an established parser as a base

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, others not so much. 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 somewhat less flexible than other options out there, and requires the help message change if you need to make changes.

docopt is also excellent at translating arguments into Rust types automatically. There is even a syntax extension which will do all this for you, ifou to manually translate from arguments to Rust types). To use BurntSushi's words, docopt is also somewhat of a black box. You get what you get, and it's hard to tweak implementation or customise your 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, but it's something to keep in mind.

Reasons to use docopt instead of clap * You want automatic translation from arguments to Rust types, and are using a nightly compiler * Performance isn't a concern * You don't have any complex relationships between arguments

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

clap is fast, and as lightweight as possible while still giving all the features you'd expect from a modern argument parser. If you use clap when just need some simple arguments parsed, you'll find it a walk in the park. But 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.

Quick Examples

The following examples show a quick example of some of the very basic functionality of clap. For more advanced usage, such as requirements, exclusions, groups, multiple values and occurrences see the video tutorials, documentation, or examples/ directory of this crate's repository.

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

// (Full example with detailed comments in examples/01a_quick_example.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")
        .args_from_usage(
            "-c --config=[CONFIG] 'Sets a custom config file'
             <INPUT> 'Sets the input file to use'
             [debug]... -d 'Sets the level of debugging information'")
        .subcommand(SubCommand::with_name("test")
            .about("controls testing features")
            .version("1.3")
            .author("Someone E. <someone_else@other.com>")
            .arg_from_usage(
                "-v --verbose 'Print test information verbosely'"))
        .get_matches();

    // 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());

    // 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);

    // Vary the output based on how many times the user used the "debug"
    // flag (i.e. 'myapp -d -d -d' or 'myapp -ddd' vs 'myapp -d')
    match matches.occurrences_of("debug") {
        0 => println!("Debug mode is off"),
        1 => println!("Debug mode is kind of on"),
        2 => println!("Debug mode is on"),
        3 | _ => println!("Don't be crazy"),
    }

    // You can 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("verbose") {
            println!("Printing verbosely...");
        } else {
            println!("Printing normally...");
        }
    }

    // more program logic goes here...
}

The following example is functionally the same as the one above, but this method allows more advanced configuration options (not shown in this small example), or even dynamically generating arguments when desired. Both methods can be used together to get the best of both worlds (see the documentation, examples/, or video tutorials).

// (Full example with detailed comments in examples/01b_quick_example.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("myapp")
        .version("1.0")
        .author("Kevin K. <kbknapp@gmail.com>")
        .about("Does awesome things")
        .arg(Arg::with_name("CONFIG")
            .short("c")
            .long("config")
            .help("Sets a custom config file")
            .takes_value(true))
        .arg(Arg::with_name("INPUT")
            .help("Sets the input file to use")
            .required(true)
            .index(1))
        .arg(Arg::with_name("debug")
            .short("d")
            .multiple(true)
            .help("Sets the level of debugging information"))
        .subcommand(SubCommand::with_name("test")
            .about("controls testing features")
            .version("1.3")
            .author("Someone E. <someone_else@other.com>")
            .arg(Arg::with_name("verbose")
                .short("v")
                .help("print test information verbosely")))
        .get_matches();

    // 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());

    // 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);

    // Vary the output based on how many times the user used the "debug"
    // flag (i.e. 'myapp -d -d -d' or 'myapp -ddd' vs 'myapp -d')
    match matches.occurrences_of("debug") {
        0 => println!("Debug mode is off"),
        1 => println!("Debug mode is kind of on"),
        2 => println!("Debug mode is on"),
        3 | _ => println!("Don't be crazy"),
    }

    // You can 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("verbose") {
            println!("Printing verbosely...");
        } else {
            println!("Printing normally...");
        }
    }

    // more program logic goes here...
}

The following combines the previous two examples by using the simplicity of the from_usage methods and the performance of the Builder Pattern.

// (Full example with detailed comments in examples/01c_quick_example.rs)
//
// This example demonstrates clap's "usage strings" method of creating
// arguments which is less verbose
#[macro_use]
extern crate clap;

fn main() {
    let matches = clap_app!(myapp =>
        (version: "1.0")
        (author: "Kevin K. <kbknapp@gmail.com>")
        (about: "Does awesome things")
        (@arg CONFIG: -c --config +takes_value "Sets a custom config file")
        (@arg INPUT: +required "Sets the input file to use")
        (@arg debug: -d ... "Sets the level of debugging information")
        (@subcommand test =>
            (about: "controls testing features")
            (version: "1.3")
            (author: "Someone E. <someone_else@other.com>")
            (@arg verbose: -v --verbose "Print test information verbosely")
        )
    ).get_matches();

    // 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());

    // 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);

    // Vary the output based on how many times the user used the "debug"
    // flag (i.e. 'myapp -d -d -d' or 'myapp -ddd' vs 'myapp -d')
    match matches.occurrences_of("debug") {
        0 => println!("Debug mode is off"),
        1 => println!("Debug mode is kind of on"),
        2 => println!("Debug mode is on"),
        3 | _ => println!("Don't be crazy"),
    }

    // You can 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("verbose") {
            println!("Printing verbosely...");
        } else {
            println!("Printing normally...");
        }
    }

    // more program logic goes here...
}

This final method shows how you can use a YAML file to build your CLI and keep your Rust source tidy. 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):

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

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

// (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 = load_yaml!("cli.yml");
    let matches = App::from_yaml(yaml).get_matches();

// 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());

// 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);

// Vary the output based on how many times the user used the "debug"
flag
    // (i.e. 'myapp -d -d -d' or 'myapp -ddd' vs 'myapp -d'
    match matches.occurrences_of("debug") {
        0 => println!("Debug mode is off"),
        1 => println!("Debug mode is kind of on"),
        2 => println!("Debug mode is on"),
        3 | _ => println!("Don't be crazy"),
    }

// You can 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("verbose") {
            println!("Printing verbosely...");
        } else {
            println!("Printing normally...");
        }
    }

    // more program logic goes here...
}

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

NOTE: The YAML option requires adding a special features flag when compiling clap because it is not compiled by default since it takes additional dependencies that some people may not need. Simply change your clap = "1" to clap = {version = "1", features = ["yaml"]} in your Cargo.toml to use the YAML version.

$ myapp --help
myapp 1.0
Kevin K. <kbknapp@gmail.com>
Does awesome things

USAGE:
    MyApp [FLAGS] [OPTIONS] <INPUT> [SUBCOMMAND]

FLAGS:
    -d               Turn debugging information on
    -h, --help       Prints this message
    -V, --version    Prints version information

OPTIONS:
    -c, --config <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:

Clone the repo $ git clone https://github.com/kbknapp/clap-rs && cd clap-rs/clap-tests
Compile the example $ cargo build --release
Run the help info $ ./target/release/claptests --help
Play with the arguments!

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 = "1"

Add the following to your src/main.rs

extern crate clap;
use clap::App;

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

Build your program $ cargo build --release
Run w/ help or version $ ./target/release/fake --help or $ ./target/release/fake --version

Usage

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

 [dependencies]
 clap = "1"

Or track the latest on the master branch at github:

[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:

[dependencies.clap]
version = "1"
default-features = false

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

[dependencies.clap]
version = "1"
default-features = false

# Cherry-pick the features you'd like to use
features = [ "suggestions", "color" ]

The following is a list of optional clap features:

"suggestions": Turns on the Did you mean '--myoption' ? feature for when users make typos.
"color": Turns on red error messages. This feature only works on non-Windows OSs.
"lints": This is not included by default and should only be used while developing to run basic lints against changes. This can only be used on Rust nightly.

Dependencies Tree

The following graphic depicts claps dependency graph.

Dashed Line: Optional dependency
Red Color: NOT included by default (must use cargo features to enable)

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]video tutorials that I've been working on.

Note: Two new videos have just been added (08 From Usage, and 09 Typed Values), if you're already familiar with clap but want to know more about these two details you can check out those videos without watching the previous few.

Note: Apologies for the resolution of the first video, it will be updated to a better resolution soon. The other videos have a proper resolution.

Running the tests

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

cargo test --features yaml && make -C clap-tests test

License

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

Macros

arg_enum!	Convenience macro to generate more complete enums with variants to be used as a type when parsing arguments. This enum also provides a `variants()` function which can be used to retrieve a `Vec<&'static str>` of the variant names.
clap_app!	App, Arg, SubCommand and Group builder macro (Usage-string like input)
crate_version!	Allows you pull the version for an from your Cargo.toml as MAJOR.MINOR.PATCH_PKGVERSION_PRE
simple_enum!	Convenience macro generated a simple enum with variants to be used as a type when parsing arguments. This enum also provides a `variants()` function which can be used to retrieve a `Vec<&'static str>` of the variant names.
value_t!	Convenience macro getting a typed value `T` where `T` implements `std::str::FromStr` This macro returns a `Result<T,String>` which allows you as the developer to decide what you'd like to do on a failed parse. There are two types of errors, parse failures and those where the argument wasn't present (such as a non-required argument).
value_t_or_exit!	Convenience macro getting a typed value `T` where `T` implements `std::str::FromStr` This macro returns a `T` or `Vec<T>` or exits with a usage string upon failure. This removes some of the boiler plate to handle failures from value_t! above.

Structs

App	Used to create a representation of a command line program and all possible command line arguments.
Arg	The abstract representation of a command line argument used by the consumer of the library. Used to set all the options and relationships that define a valid argument for the program.
ArgGroup	`ArgGroup`s are a family of related arguments and way for you to say, "Any of these arguments". By placing arguments in a logical group, you can make easier requirement and exclusion rules instead of having to list each individually, or when you want a rule to apply "any but not all" arguments.
ArgMatches	Used to get information about the arguments that where supplied to the program at runtime by the user. To get a new instance of this struct you use `.get_matches()` of the `App` struct.
ClapError	Command line argument parser error
SubCommand	The abstract representation of a command line subcommand used by the consumer of the library.

Enums

AppSettings	Application level settings, which affect how `App` operates
ClapErrorType	Command line argument parser error types
Format	Defines styles for different types of error messages. Defaults to Error=Red, Warning=Yellow, and Good=Green