[](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/terminal applications.
* **ArgsNegateSubcommands:** disables args being allowed between subcommands
* **DontCollapseArgsInUsage:** disables the collapsing of positional args into `[ARGS]` in the usage string
* **DisableHelpSubcommand:** disables building the `help` subcommand
* **AllowMissingPositional:** allows one to implement `$ prog [optional] <required>` style CLIs where the second postional argument is required, but the first is optional
* **PropagateGlobalValuesDown:** automatically propagats global arg's values down through *used* subcommands
* **Arg::value_terminator:** adds the ability to terminate multiple values with a given string or char
* **Arg::default_value_if[s]:** adds new methods for *conditional* default values (such as a particular value from another argument was used)
* **Arg::requires_if[s]:** adds the ability to *conditionally* require additional args (such as if a particular value was used)
* **Arg::required_if[s]:** adds the ability for an arg to be *conditionally* required (i.e. "arg X is only required if arg Y was used with value Z")
* **Arg::validator_os:** adds ability to validate values which may contain invalid UTF-8
* **crate_description!:** Uses the `Cargo.toml` description field to fill in the `App::about` method at compile time
* **crate_name!:** Uses the `Cargo.toml` name field to fill in the `App::new` method at compile time
* **app_from_crate!:** Combines `crate_version!`, `crate_name!`, `crate_description!`, and `crate_authors!` into a single macro call to build a default `App` instance from the `Cargo.toml` fields
* **no_cargo:** adds a `no_cargo` feature to disable Cargo-env-var-dependent macros for those *not* using `cargo` to build their crates
* **Options:** fixes a critical bug where options weren't forced to have a value
* fixes a bug where calling the help of a subcommand wasn't ignoring required args of parent commands
* **Help Subcommand:** fixes a bug where the help subcommand couldn't be overriden
* **Low Index Multiples:** fixes a bug which caused combinations of LowIndexMultiples and `Arg::allow_hyphen_values` to fail parsing
* **Default Values:** improves the error message when default values are involved
* **YAML:** adds conditional requirements and conditional default values to YAML
* Support `--("some-arg-name")` syntax for defining long arg names when using `clap_app!` macro
* Support `("some app name")` syntax for defining app names when using `clap_app!` macro
* **Help Wrapping:** long app names (with spaces), authors, and descriptions are now wrapped appropriately
* **Conditional Default Values:** fixes the failing doc tests of Arg::default_value_ifs
* **Conditional Requirements:** adds docs for Arg::requires_ifs
* Fixes a bug where calling the help of a subcommand wasn't ignoring required args of parent commands
* **AppSettings:** adds new setting `AppSettings::AllowNegativeNumbers` which functions like `AllowLeadingHyphen` except only allows undefined negative numbers to pass parsing.
* **Value Delimiters:** fixes the confusion around implicitly setting value delimiters. (The default is to *not* use a delimiter unless explicitly set)
* Changes the default value delimiter rules (i.e. the default is `use_delimiter(false)`*unless* a setting/method that implies multiple values was used) **[Bugfix that *may* "break" code]**
* If code breaks, simply add `Arg::use_delimiter(true)` to the affected args
* Adds ability to hide the possible values from the help text on a per argument basis, instead of command wide
* Allows for limiting detected terminal width (i.e. wrap at `x` length, unless the terminal width is *smaller*)
*`clap` now ignores hard newlines in help messages and properly re-aligns text, but still wraps if the term width is too small
* Adds support for the setting `Arg::require_delimiter` from YAML
* **Completions:** one can now [generate a bash completions](https://docs.rs/clap/2.9.0/clap/struct.App.html#method.gen_completions) script at compile time! These completions work with options using [possible values](https://docs.rs/clap/2.9.0/clap/struct.Arg.html#method.possible_values), [subcommand aliases](https://docs.rs/clap/2.9.0/clap/struct.App.html#method.aliases), and even multiple levels of subcommands
* **Arg:** adds new optional setting [`Arg::require_delimiter`](https://docs.rs/clap/2.8.0/clap/struct.Arg.html#method.require_delimiter) which requires val delimiter to parse multiple values
* Options using multiple values and delimiters no longer parse additional values after a trailing space (i.e. `prog -o 1,2 file.txt` parses as `1,2` for `-o` and `file.txt` for a positional arg)
* Using options using multiple values and with an `=` no longer parse args after the trailing space as values (i.e. `prog -o=1 file.txt` parses as `1` for `-o` and `file.txt` for a positional arg)
* **Pull crate Authors from Cargo.toml**: One can now use the `crate_authors!` macro to automatically pull the crate authors from their Cargo.toml file
* **Help text auto wraps and aligns at for subcommands too!** - Long help strings of subcommands will now properly wrap and align to term width on Linux and OS X. This can be turned off as well.
* **Help text auto wraps and aligns at term width!** - Long help strings will now properly wrap and align to term width on Linux and OS X (and presumably 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-arrange 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!
* **Help subcommand now accepts other subcommands as arguments!** - Similar to other CLI precedents, the `help` subcommand can now accept other subcommands as arguments to display their help message. i.e. `$ myprog help mysubcmd` (*Note* these can even be nested heavily such as `$ myprog help subcmd1 subcmd2 subcmd3` etc.)
* **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](https://docs.rs/clap/) and [examples/](examples) directory
* **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`)
* **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/Overrides** - In POSIX args can be conflicting, but not fail parsing because whichever arg comes *last* "wins" so 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](https://docs.rs/clap/), [examples/](examples) directory of this repository or the [video tutorials](https://www.youtube.com/playlist?list=PLza5oFLQGTl2Z5T8g1pRkIynR3E0_pc7U).
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.
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.
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:
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.
```rust
#[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")
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**: If you are concerned with supporting a minimum version of Rust that is *older* than the current stable Rust minus 2 stable releases, it's recommended to use the `~major.minor.patch` style versions in your `Cargo.toml` which will only update the patch version automatically. For more information see the [Compatibility Policy](#compatibility-policy))
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 :)
Alternatively, if you have [`just`](https://github.com/casey/just) installed you can run the prebuilt recipies. *Not* using `just` is prfeclty fine as well, it simply bundles commands automatically.
During the CI process `clap` runs against many different lints using [`clippy`](https://github.com/Manishearth/rust-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:
```sh
$ rustup override add nightly
$ cargo build --features lints
$ rustup override remove
# Or
$ 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:
```sh
$ cargo test --features debug
# Or for individual tests
$ cargo test --test <test_name> --features debug
# The corresponding just command for individual debugging tests is:
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` 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 suprised of breaking changes, it is **highly** recommended to use the `~major.minor.patch` style in your `Cargo.toml` only if you wish to target a version of Rust that is *older* than current stable minus two releases:
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.
`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 1.13.0, meaning `clap` is guaranteed to compile with 1.11.0 and beyond.
At the 1.14.0 release, `clap` will be guaranteed to compile with 1.12.0 and beyond, etc.
`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`
