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I've been working on a few short video tutorials about using `clap`. They're located on [youtube](https://www.youtube.com/playlist?list=PLza5oFLQGTl0Bc_EU_pBNcX-rhVqDTRxv).
*Note*: The videos have not been updated to include the new `from_usage()` methods which make building args significantly less verbose. New videos will be added soon.
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 is different about `clap` from other options available is the very simple almost 'Pythonic' style in which you define the valid available arguments for your program, while still giving advanced features. `clap` allows you express complex relationships between arguments in a very simple manner. This means you don't have to spend tons time learning an entirely new library's structures and use. The basics of `clap` can be learned almost intuitively.
`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 (or only defined some of them), `clap` will auto-generate 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.
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
* **Get Version from Cargo.toml**: `clap` is fully compatible with Rust's `env!()` macro for automatically getting the version from your Cargo.toml. See `examples/09_AutoVersion.rs` for how to do this (Thanks to [jhelwig](https://github.com/jhelwig) for pointing this out)
The following two examples (which are functionally equivilant, but show two different ways to use `clap`) show a quick example of some of the 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.
While the following example is functionally the same as the one above, this method allows more advanced configuration options, or even dynamically generating arguments when desired. Both methods can be used together to get the best of both worlds (see the documentation).
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)
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).
