clap 0.5.6

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Command Line Argument Parser written in Rust

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

You can use clap to lay out a list of possible valid command line arguments and subcommands, then let clap parse and validate the string given by the user at runtime. This means you focus on your applications functionality, not parsing and validating arguments.

What seperates clap from other options available is the very simple almost 'Pythonic' style in which you define the valid available arguments for your program. This means you don't have to spend tons time learning an entirely new library's structures and use.

clap also provides all the traditional version and help switches (or flags) 'for free' by parsing the list of developer supplied arguments. If the developer hasn't defined them already, clap will auto-generate only the applicable "help" and "version" switches (as well as a "help" subcommand so long as other subcommands have been manually defined as well).

After defining a list of possible valid arguments and subcommands, clap parses the string given by the end-user at runtime then gives you a list of the valid matches and their values. If the user made an error or typo, clap informs them and exits gracefully. This means that you can simply use these matches and values to determine the functioning of your program.

Quick Example

// (Full example with comments in examples/
extern crate clap;
use clap::{Arg, App, SubCommand};

fn main() {
    let matches = App::new("MyApp")
                          .author("Kevin K. <>")
                          .about("Does awesome things")
                               .help("Sets a custom config file")
                               .help("Sets an optional output file")
                               .help("Turn debugging information on"))
                                      .about("controls testing features")
                                          .help("print test information verbosely")))

    if let Some(o) = matches.value_of("output") {
        println!("Value for output: {}", o);

    if let Some(c) = matches.value_of("CONFIG") {
        println!("Value for config: {}", c);

    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"),

    if let Some(ref matches) = matches.subcommand_matches("test") {
        if matches.is_present("verbose") {
            println!("Printing verbosely...");
        } else {
            println!("Printing normally...");

    // more porgram logic goes here...

If you were to compile the above program and run it with the flag --help or -h (or help subcommand, since we defined test as a subcommand) the following output woud be presented

$ myprog --help
MyApp 1.0
Kevin K. <>
Does awesome things


    -d               Turn debugging information on
    -h,--help        Prints this message
    -v,--version     Prints version information
    -c,--config=CONFIG        Sets a custom config file

    output            Sets an optional output file

    help            Prints this message
    test            Controls testing features


Add clap as a dependecy in your Cargo.toml file to use from

clap = "*"

Or track the latest on the master branch at github:

git = ""

Then run cargo build or cargo update for your project.


Add extern crate clap; to your crate root.

More Information

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

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

How to build

Clone the repo (master branch if using clap, dev branch if contributing) and build with Cargo

git clone
cd clap-rs
cargo build --release

Running the tests

If contributing, you can run the tests as follows (assuming you've already cloned the repo to clap-rs/

cd clap-rs/claptests
make test

Building the documentation

Run this instead of cargo doc to generate the proper module docstring:

make doc

Then browse to clap-rs/docs/index.html in your web-browser of choice