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.
Created by gh-md-toc
If you're already familiar with clap but just want to see some new highlights as of 1.5
For full details, see CHANGELOG.md
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.
For a full FAQ and more in depth details, see the wiki page
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!
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 somewhat of a performance boost. Although, as you start implementing additional features, 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.
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 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, and requires you to change the help message 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, 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 customise 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.
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 the fact it remains about as fast as getopts is great. 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.
Below are a few of the features which clap supports, full descriptions and usage can be found in the documentation and examples/ directory
-f and --flag respectively)-fBgoZ is the same as -f -B -g -o -Z)-vvv or -v -v -v)myprog <file>... such as myprog file1.txt file2.txt being two values for the same "file" argument)-- meaning, only positional arguments follow-o value or -ovalue and --option value or --option=value respectively)-o <value> -o <other_value> or the shorthand -o <value> <other_value>)-o <name> <other_name> etc. for when you require specific multiple valuesgit add <file> where add is a sub-command of git)
--mode option which may only have one of two values fast or slow such as --mode fast or --mode slow)clap you can achieve this exact functionality from Rust's Option<&str>.unwrap_or("some default") method (or Result<T,String>.unwrap_or(T) when using typed values)clap is fully compatible with Rust's env!() macro for automatically setting the version of your application to the version in your Cargo.toml. See 09autoversion example for how to do this (Thanks to jhelwig for pointing this out)clap to get typed values (i.e. i32, u8, etc.) from positional or option arguments so long as the type you request implements std::str::FromStr See the 12typedvalues example. You can also use claps simple_enum! or arg_enum! macro to create an enum with variants that automatically implements std::str::FromStr. See 13aenumvalues_automatic example for details and performs an ascii case insensitive parse from a string->enum.--myoption <value> argument, and the user mistakenly typed --moyption value (notice y and o switched), they would receive a Did you mean '--myoption' ? error and exit gracefully. This also works for subcommands and flags. (Thanks to Byron for the implementation) (This feature can optionally be disabled, see 'Optional Dependencies / Features')alias ls='ls -l' but then using ls -C in your terminal which ends up passing ls -l -C as the final arguments. Since -l and -C aren't compatible, this effectively runs ls -C in clap if you choose...clap also supports hard conflicts that fail parsing). (Thanks to Vinatorul!)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 repository.
NOTE: All these examples are functionally the same, but show three different styles in which to use clap
```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=[CONFIG] 'Sets a custom config file' 'Sets the input file to use' [debug]... -d 'Sets the level of debugging information'") .subcommand(SubCommand::withname("test") .about("controls testing features") .version("1.3") .author("Someone E. someone_else@other.com") .argfromusage("-v --verbose 'Print test information verbosely'")) .getmatches();
// 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).
```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("myapp") .version("1.0") .author("Kevin K. kbknapp@gmail.com") .about("Does awesome things") .arg(Arg::withname("CONFIG") .short("c") .long("config") .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("debug") .short("d") .multiple(true) .help("Sets the level of debugging information")) .subcommand(SubCommand::withname("test") .about("controls testing features") .version("1.3") .author("Someone E. someone_else@other.com") .arg(Arg::withname("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.
```rust // (Full example with detailed comments in examples/01cquickexample.rs) // // This example demonstrates clap's "usage strings" method of creating arguments which is less // less verbose
extern crate clap;
fn main() { let matches = clapapp!(myapp => (version: "1.0") (author: "Kevin K. kbknapp@gmail.com") (about: "Does awesome things") (@arg CONFIG: -c --config +takesvalue "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):
yaml
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:
```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.
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();
// 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.
```sh $ myapp --help myapp 1.0 Kevin K. kbknapp@gmail.com Does awesome things
USAGE: MyApp [FLAGS] [OPTIONS] [SUBCOMMAND]
FLAGS: -d Turn debugging information on -h, --help Prints this message -V, --version Prints version information
OPTIONS:
-c, --config
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.
To try out the pre-built example, use the following steps:
$ git clone https://github.com/kbknapp/clap-rs && cd clap-rs/clap-tests$ cargo build --release$ ./target/release/claptests --helpTo 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"
src/main.rs```rust extern crate clap; use clap::App;
fn main() { let _ = App::new("fake").version("v1.0-beta").get_matches(); } ```
$ cargo build --release$ ./target/release/fake --help or $ ./target/release/fake --versionFor full usage, add clap as a dependency in your Cargo.toml file to use from crates.io:
toml
[dependencies]
clap = "1"
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.
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 = "1"
default-features = false
You can also selectively enable only the features you'd like to include, by adding:
```toml [dependencies.clap] version = "1" default-features = false
features = [ "suggestions", "color" ] ```
The following is a list of optional clap features:
Did you mean '--myoption' ? feature for when users make typos.The following graphic depicts claps dependency graph (generated using cargo-graph).
features to enable)
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.
There's also the video tutorial series Argument Parsing with Rust 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.
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.
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
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).
clap should be low since the main program is the star of the showpanic! on developer error, exit gracefully on end-user errorclap is licensed under the MIT license. Please read the LICENSE-MIT file in this repository for more information.
Although I do my best to keep breaking changes to a minimum, there are breaking changes from time to time in order to support better features or implementation. For the full details, see CHANGELOG.md.
As of 1.3.0
ArgGroup::add_all now takes &[&str] instead of a Vec<&str>ArgGroup::requires_all now takes &[&str] instead of a Vec<&str>ArgGroup::conflicts_with_all now takes &[&str] instead of a Vec<&str>As of 0.11.0: The default short flag for version has changed from -v to -V (Uppercase). Although you can also now override the short flag for help and version using App::help_short() and App::version_short()
As of 0.7.0
Arg::possible_values(), Arg::value_names(), Arg::requires_all(), Arg::mutually_excludes_all() [deprecated], Arg::conflicts_with_all()Vec<&str>, instead they take a generic IntoIterator<Item=AsRef<str>> which means you cannot use an inline vec![] but it means the methods are now far more flexible, especially for dynamic value generation.IntoIterator trait, or something like:rust
let my_vals = ["value1", "value2", "value3"];
...
.possible_values(&my_vals)
Old method names will be left around for some time.
As of 1.2.0 (Will not be removed until 2.x)
App::subcommands_negate_reqs(bool) -> AppSettings::SubcommandsNegateReqs passed to App::setting()App::subcommand_required(bool) -> AppSettings::SubcommandRequired passed to App::setting()App::arg_required_else_help(bool) -> AppSettings::ArgRequiredElseHelp passed to App::setting()App::global_version(bool) -> AppSettings::GlobalVersion passed to App::setting()App::versionless_subcommands(bool) -> AppSettings::VersionlessSubcommands passed to App::setting()App::unified_help_messages(bool) -> AppSettings::UnifiedHelpMessages passed to App::setting()App::wait_on_error(bool) -> AppSettings::WaitOnError passed to App::setting()App::subcommand_required_else_help(bool) -> AppSettings::SubcommandRequiredElseHelp passed to App::setting()As of 0.10.0
SubCommand::new() -> SubCommand::with_name() (Removed as of 1.0.0)App::error_on_no_subcommand() -> App::subcommand_required() (Removed as of 1.0.0)Arg::new() -> Arg::with_name() (Removed as of 1.0.0)Arg::mutually_excludes() -> Arg::conflicts_with() (Removed as of 1.0.0)Arg::mutually_excludes_all() -> Arg::conflicts_with_all() (Removed as of 1.0.0)