Expand description
clap
is a simple-to-use, efficient, and full-featured library for parsing command line
arguments and subcommands when writing console/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 the 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.
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.
NOTE: All of these examples are functionally the same, but show different styles in which to
use clap
The first example shows 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.
// (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("My Super Program")
.version("1.0")
.author("Kevin K. <kbknapp@gmail.com>")
.about("Does awesome things")
.arg(Arg::with_name("config")
.short("c")
.long("config")
.value_name("FILE")
.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("v")
.short("v")
.multiple(true)
.help("Sets the level of verbosity"))
.subcommand(SubCommand::with_name("test")
.about("controls testing features")
.version("1.3")
.author("Someone E. <someone_else@other.com>")
.arg(Arg::with_name("debug")
.short("d")
.help("print debug information verbosely")))
.get_matches();
// 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 next example shows a far less verbose method, but sacrifices some of the advanced configuration options (not shown in this small example). This method also takes a very minor runtime penalty.
// (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 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=[FILE] 'Sets a custom config file'
<INPUT> 'Sets the input file to use'
-v... 'Sets the level of verbosity'")
.subcommand(SubCommand::with_name("test")
.about("controls testing features")
.version("1.3")
.author("Someone E. <someone_else@other.com>")
.arg_from_usage("-d, --debug 'Print debug information'"))
.get_matches();
// Same as previous example...
}
This third 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:
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
Since this feature requires additional dependencies that not everyone may want, it is not compiled in by default and we need to enable a feature flag in Cargo.toml:
Simply change your clap = "~2.27.0"
to clap = {version = "~2.27.0", features = ["yaml"]}
.
At last 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();
// Same as previous examples...
}
Finally there is a macro version, which is like a hybrid approach offering the speed of the builder pattern (the first example), but without all the verbosity.
#[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();
// Same as before...
}
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
$ myprog --help
My Super Program 1.0
Kevin K. <kbknapp@gmail.com>
Does awesome things
USAGE:
MyApp [FLAGS] [OPTIONS] <INPUT> [SUBCOMMAND]
FLAGS:
-h, --help Prints this message
-v Sets the level of verbosity
-V, --version Prints version information
OPTIONS:
-c, --config <FILE> 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 repository
$ git clone https://github.com/clap-rs/clap && cd clap-rs/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 yourCargo.toml
[dependencies]
clap = "2"
- Add the following to your
src/main.rs
extern crate clap;
use clap::App;
fn main() {
App::new("fake").version("v1.0-beta").get_matches();
}
- Build your program
$ cargo build --release
- Run with 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
(it is highly recommended to
use the ~major.minor.patch
style versions in your Cargo.toml
, for more information see
Compatibility Policy) to use from crates.io:
[dependencies]
clap = "~2.27.0"
Or get the latest changes from the master branch at github:
[dependencies.clap]
git = "https://github.com/clap-rs/clap.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
Features enabled by default
suggestions
: Turns on theDid you mean '--myoption'?
feature for when users make typos. (builds dependencystrsim
)color
: Turns on colored error messages. This feature only works on non-Windows OSs. (builds dependencyansi-term
andatty
)wrap_help
: Wraps the help at the actual terminal width when available, instead of 120 characters. (builds dependencytextwrap
with featureterm_size
)
To disable these, add this to your Cargo.toml
:
[dependencies.clap]
version = "~2.27.0"
default-features = false
You can also selectively enable only the features you’d like to include, by adding:
[dependencies.clap]
version = "~2.27.0"
default-features = false
features = [ "suggestions", "color" ]
Opt-in features
- “yaml”: Enables building CLIs from YAML documents. (builds dependency
yaml-rust
) - “unstable”: Enables unstable
clap
features that may change from release to release
Dependencies Tree
The following graphic depicts clap
s dependency graph (generated using
cargo-graph).
- Dashed Line: Optional dependency
- Red Color: NOT included by default (must use cargo
features
to enable) - Blue Color: Dev dependency, only used while developing.
More Information
You can find complete documentation on the docs.rs 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 v2.
These videos slowly trickle out as I finish them and currently a work in progress.
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.
Testing Code
To test with all features both enabled and disabled, you can run theese commands:
$ cargo test --no-default-features
$ cargo test --features "yaml unstable"
Alternatively, if you have just
installed you can run the
prebuilt recipes. Not using just
is perfectly fine as well, it simply bundles commands
automatically.
For example, to test the code, as above simply run:
$ just run-tests
From here on, I will list the appropriate cargo
command as well as the just
command.
Sometimes it’s helpful to only run a subset of the tests, which can be done via:
$ cargo test --test <test_name>
$ just run-test <test_name>
Linting Code
During the CI process clap
runs against many different lints using
clippy
. In order to check if these lints pass on
your own computer prior to submitting a PR you’ll need a nightly compiler.
In order to check the code for lints run either:
$ rustup override add nightly
$ cargo build --features lints
$ rustup override remove
$ just lint
Debugging Code
Another helpful technique is to see the clap
debug output while developing features. In order
to see the debug output while running the full test suite or individual tests, run:
$ cargo test --features debug
$ cargo test --test <test_name> --features debug
$ just debug <test_name>
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).
- Remain backwards compatible when possible
- If backwards compatibility must be broken, use deprecation warnings if at all possible before removing legacy code - This does not apply for security concerns
- Parse arguments quickly
- Parsing of arguments shouldn’t slow down usage of the main program - This is also true of generating help and usage information (although slightly less stringent, as the program is about to exit)
- Try to be cognizant of memory usage
- Once parsing is complete, the memory footprint of
clap
should be low since the main program is the star of the show
- Once parsing is complete, the memory footprint of
panic!
on developer error, exit gracefully on end-user error
Compatibility Policy
Because clap
takes SemVer
and compatibility seriously, this is the official policy regarding
breaking changes and previous versions of Rust.
clap
will pin the minimum required version of Rust to the CI builds. Bumping the minimum
version of Rust is considered a minor breaking change, meaning at a minimum the minor version
of clap
will be bumped.
In order to keep from being surprised by breaking changes, it is highly recommended to use
the ~major.minor.patch
style in your Cargo.toml
:
[dependencies] clap = "~2.27.0"
This will cause only the patch version to be updated upon a cargo update
call, and therefore
cannot break due to new features, or bumped minimum versions of Rust.
Minimum Version of Rust
clap
will officially support current stable Rust, minus two releases, but may work with prior
releases as well. For example, current stable Rust at the time of this writing is 1.21.0,
meaning clap
is guaranteed to compile with 1.19.0 and beyond. At the 1.22.0 release, clap
will be guaranteed to compile with 1.20.0 and beyond, etc.
Upon bumping the minimum version of Rust (assuming it’s within the stable-2 range), it must be
clearly annotated in the CHANGELOG.md
License
clap
is licensed under the MIT license. Please read the LICENSE-MIT file in
this repository for more information.
Macros
Counts the number of comma-delimited expressions passed to it. The result is a compile-time
evaluable expression, suitable for use as a static array size, or the value of a const
.
Allows you to build the App
instance from your Cargo.toml at compile time.
Build App
, Arg
s, SubCommand
s and Group
s with Usage-string like input
but without the associated parsing runtime cost.
Allows you to pull the authors for the app from your Cargo.toml at
compile time in the form:
"author1 lastname <author1@example.com>:author2 lastname <author2@example.com>"
Allows you to pull the description from your Cargo.toml at compile time.
Allows you to pull the name from your Cargo.toml at compile time.
Allows you to pull the version from your Cargo.toml at compile time as
MAJOR.MINOR.PATCH_PKGVERSION_PRE
Convenience macro getting a typed value T
where T
implements std::str::FromStr
from an
argument value. 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). You can use
it to get a single value, or a iterator as with the ArgMatches::values_of
Convenience macro getting a typed value T
where T
implements std::str::FromStr
or
exiting upon error, instead of returning a Result
type.
Convenience macro getting a typed value Vec<T>
where T
implements std::str::FromStr
This macro returns a clap::Result<Vec<T>>
which allows you as the developer to decide
what you’d like to do on a failed parse.
Convenience macro getting a typed value Vec<T>
where T
implements std::str::FromStr
or exiting upon error.
Structs
Used to create a representation of a command line program and all possible command line
arguments. Application settings are set using the “builder pattern” with the
App::get_matches
family of methods being the terminal methods that starts the
runtime-parsing process. These methods then return information about the user supplied
arguments (or lack there of).
The abstract representation of a command line argument. Used to set all the options and relationships that define a valid argument for the program.
ArgGroup
s are a family of related arguments and way for you to express, “Any of these
arguments”. By placing arguments in a logical group, you can create easier requirement and
exclusion rules instead of having to list each argument individually, or when you want a rule
to apply “any but not all” arguments.
Used to get information about the arguments that were supplied to the program at runtime by
the user. New instances of this struct are obtained by using the App::get_matches
family of
methods.
Command Line Argument Parser Error
An iterator for getting multiple values out of an argument via the ArgMatches::values_of_os
method. Usage of this iterator allows values which contain invalid UTF-8 code points unlike
Values
.
The abstract representation of a command line subcommand.
An iterator for getting multiple values out of an argument via the ArgMatches::values_of
method.
Enums
Application level settings, which affect how App
operates
Various settings that apply to arguments and may be set, unset, and checked via getter/setter
methods Arg::set
, Arg::unset
, and Arg::is_set
Command line argument parser kind of error
Describes which shell to produce a completions file for