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`clap` is used to parse *and validate* the string of command line arguments provided by the user at runtime. You simply 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 all the traditional version and help switches (or flags) 'for free.' It does this by checking list of valid possibilities you supplied and if you haven't defined those flags already (or only defined some of them), `clap` will auto-generate the applicable ones (as well as a "help" subcommand so long as other subcommands have been manually defined as well).
After `clap` finishes parsing the user provided string, it returns all 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, and worry less about error handling.
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/docs/clap/index.html) and `examples/` directory
* **Auto-generated Help, Version, and Usage information**
- Get their own auto-generated Help, Version, and Usage independant of parent
* **Requirement Rules**: Arguments can optionally define the following types of requirement rules
- Required by default
- Required only if certain arguments are present
- Can require other arguments to be present
* **Exclusion Rules**: Arguments can optionally define the following types of exclusion rules
- Can be disallowed when certain arguments are present
- Can disallow use of other arguments when present
* **Specific Value Sets**: Positional or Option Arguments can optionally 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 `examples/09_AutoVersion.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 `examples/12_TypedValues.rs`. You can also use `clap`s `simple_enum!` or `arg_enum!` macro to create an enum with variants that automatically implements `std::str::FromStr`. See `examples/13a_EnumValuesAutomatic.rs` for details.
The following two examples show a quick example of some of the very basic functionality of `clap`. For more advanced usage, such as requirements, exclusions, multiple values and occurrences see the [video tutorials](https://www.youtube.com/playlist?list=PLza5oFLQGTl0Bc_EU_pBNcX-rhVqDTRxv), [documentation](http://kbknapp.github.io/clap-rs/docs/clap/index.html), or `examples/` directory of this repository.
*NOTE:* Both examples are functionally the same, but show two different ways to use `clap`
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).
If you were to compile either 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/` directory of this repo)
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!
2. Clone your fork (`git clone https://github.com/$YOUR_USERNAME/clap-rs && cd clap-rs`)
3. Create new branch (`git checkout -b new-branch`)
4. Make your changes, and commit (`git commit -am "your message"`) (I try to use a [conventional](https://github.com/ajoslin/conventional-changelog/blob/master/CONVENTIONS.md) changelog format so I can update it using [clog](https://github.com/thoughtram/clog))
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 :)
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).
