[](https://crates.io/crates/clap) [](https://crates.io/crates/clap) [](https://github.com/kbknapp/clap-rs/blob/master/LICENSE-MIT) [](https://coveralls.io/github/kbknapp/clap-rs?branch=master) [](https://gitter.im/kbknapp/clap-rs?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
It is a simple to use, efficient, and full featured library for parsing command line arguments and subcommands when writing console, or terminal applications.
* **Help text auto wraps and aligns at term width!** - Long help strings will now properly wrap and align to term width on Linux and OSX (and resumably Unix too). This can be turned off as well.
* **Can customize the order of opts, flags, and subcommands in help messages** - Instead of using the default alphabetical order, you can now re-arange the order of your args and subcommands in help message. This helps to emphasize more popular or important options.
* **Can auto-derive the order from declaration order** - Have a bunch of args or subcommmands to re-order? You can now just derive the order from the declaration order!
* Other minor bug fixes
An example of the help text wrapping at term width:
* **Default Values**: Args can now specify default values
* **Next Line Help**: Args can have help strings on the line following the argument (useful for long arguments, or those with many values). This can be set command-wide or for individual args
`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.
For a full FAQ and more in depth details, see [the wiki page](https://github.com/kbknapp/clap-rs/wiki/FAQ)
### 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](https://github.com/rust-lang-nursery/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.
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.
`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.
Below are a few of the features which `clap` supports, full descriptions and usage can be found in the [documentation](http://kbknapp.github.io/clap-rs/clap/index.html) and [examples/](examples) directory
* **POSIX Override Rules**: Arguments can define rules to support POSIX overriding
* **Groups**: Arguments can be made part of a group
- Fully compatible with other relational rules (requirements, conflicts, and overrides) which allows things like requiring the use of any arg in a group, or denying the use of an entire group conditionally
* **Specific Value Sets**: Positional or Option Arguments can define a specific set of allowed values (i.e. imagine a `--mode` option which may *only* have one of two values `fast` or `slow` such as `--mode fast` or `--mode slow`)
* **Default Values**: Although not specifically provided by `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)
* **Automatic Version from Cargo.toml**: `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 [09_auto_version example](examples/09_auto_version.rs) for how to do this (Thanks to [jhelwig](https://github.com/jhelwig) for pointing this out)
* **Typed Values**: You can use several convenience macros provided by `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 [12_typed_values example](examples/12_typed_values.rs). You can also use `clap`s `arg_enum!` macro to create an enum with variants that automatically implement `std::str::FromStr`. See [13a_enum_values_automatic example](examples/13a_enum_values_automatic.rs) for details
* **Suggestions**: Suggests corrections when the user enters a typo. For example, if you defined a `--myoption` argument, and the user mistakenly typed `--moyption` (notice `y` and `o` transposed), they would receive a `Did you mean '--myoption' ?` error and exit gracefully. This also works for subcommands and flags. (Thanks to [Byron](https://github.com/Byron) for the implementation) (This feature can optionally be disabled, see 'Optional Dependencies / Features')
* **Colorized Errors (Non Windows OS only)**: Error message are printed in in colored text (this feature can optionally be disabled, see 'Optional Dependencies / Features').
* **Custom Validations**: You can define a function to use as a validator of argument values. Imagine defining a function to validate IP addresses, or fail parsing upon error. This means your application logic can be solely focused on *using* values.
* **POSIX Compatible Conflicts** - In POSIX args can be conflicting, but not fail parsing because whichever arg comes *last* "wins" to to speak. This allows things such as aliases (i.e. `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](https://github.com/Vinatorul)!)
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](http://kbknapp.github.io/clap-rs/clap/index.html), [examples/](examples) directory of this repository or the [video tutorials](https://www.youtube.com/playlist?list=PLza5oFLQGTl0Bc_EU_pBNcX-rhVqDTRxv) (which are quite outdated by now).
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.
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).
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):
**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
Define a list of valid arguments for your program (see the [documentation](https://kbknapp.github.io/clap-rs/index.html) or [examples/](examples) directory of this repo)
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`:
* **"suggestions"**: Turns on the `Did you mean '--myoption' ?` feature for when users make typos. (builds dependency `strsim`)
* **"color"**: Turns on colored error messages. This feature only works on non-Windows OSs. (builds dependency `ansi-term`)
* **"wrap_help"**: Automatically detects terminal width and wraps long help text lines with proper indentation alignment (builds dependency `libc`)
* **"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. (builds dependency `clippy`)
* **"unstable"**: This is **not** included by default. Enables unstable features, unstable refers to whether or not they may change, not performance stability.
There's also the video tutorial series [Argument Parsing with Rust](https://www.youtube.com/playlist?list=PLza5oFLQGTl0Bc_EU_pBNcX-rhVqDTRxv) that I've been working on.
*Note*: Two new videos have just been added ([08 From Usage](https://youtu.be/xc6VdedFrG0), and [09 Typed Values](https://youtu.be/mZn3C1DnD90)), 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/](examples) directory, or file an issue and tell me. I'm all about giving credit where credit is due :)
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` 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](./CHANGELOG.md).
* struct field `ClapError::error_type` => `Error::kind`
*`ClapResult` => `Result`
*`ClapErrorType` => `ErrorKind`
* **Removed Deprecated Functions and Methods**
*`App::subcommands_negate_reqs`
*`App::subcommand_required`
*`App::arg_required_else_help`
*`App::global_version(bool)`
*`App::versionless_subcommands`
*`App::unified_help_messages`
*`App::wait_on_error`
*`App::subcommand_required_else_help`
*`SubCommand::new`
*`App::error_on_no_subcommand`
*`Arg::new`
*`Arg::mutually_excludes`
*`Arg::mutually_excludes_all`
*`Arg::mutually_overrides_with`
*`simple_enum!`
* **Renamed Error Variants**
*`InvalidUnicode` => `InvalidUtf8`
*`InvalidArgument` => `UnknownArgument`
* **Usage Parser**
* Value names can now be specified inline, i.e. `-o, --option <FILE> <FILE2> 'some option which takes two files'`
* **There is now a priority of order to determine the name** - This is perhaps the biggest breaking change. See the documentation for full details. Prior to this change, the value name took precedence. **Ensure your args are using the proper names (i.e. typically the long or short and NOT the value name) throughout the code**
*`ArgMatches::values_of` returns an `Values` now which implements `Iterator` (should not break any code)
*`crate_version!` returns `&'static str` instead of `String`
