README.md
1clap
2====
3
4[](https://crates.io/crates/clap) [](https://crates.io/crates/clap) [](https://github.com/clap-rs/clap/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)
5
6Linux: [](https://travis-ci.org/clap-rs/clap)
7Windows: [](https://ci.appveyor.com/project/kbknapp/clap-rs/branch/master)
8
9Command Line Argument Parser for Rust
10
11It is a simple-to-use, efficient, and full-featured library for parsing command line arguments and subcommands when writing console/terminal applications.
12
13* [documentation](https://docs.rs/clap/)
14* [website](https://clap.rs/)
15* [video tutorials](https://www.youtube.com/playlist?list=PLza5oFLQGTl2Z5T8g1pRkIynR3E0_pc7U)
16
17Table of Contents
18=================
19
20* [About](#about)
21* [FAQ](#faq)
22* [Features](#features)
23* [Quick Example](#quick-example)
24* [Try it!](#try-it)
25 * [Pre-Built Test](#pre-built-test)
26 * [BYOB (Build Your Own Binary)](#byob-build-your-own-binary)
27* [Usage](#usage)
28 * [Optional Dependencies / Features](#optional-dependencies--features)
29 * [Dependencies Tree](#dependencies-tree)
30 * [More Information](#more-information)
31 * [Video Tutorials](#video-tutorials)
32* [How to Contribute](#how-to-contribute)
33 * [Compatibility Policy](#compatibility-policy)
34 * [Minimum Version of Rust](#minimum-version-of-rust)
35* [Related Crates](#related-crates)
36* [License](#license)
37* [Recent Breaking Changes](#recent-breaking-changes)
38 * [Deprecations](#deprecations)
39
40Created by [gh-md-toc](https://github.com/ekalinin/github-markdown-toc)
41
42## About
43
44`clap` is used to parse *and validate* the string of command line arguments provided by a 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.
45
46`clap` provides many things 'for free' (with no configuration) including the traditional version and help switches (or flags) along with associated messages. If you are using subcommands, `clap` will also auto-generate a `help` subcommand and separate associated help messages.
47
48Once `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 with a friendly message 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 prior to your applications main execution.
49
50## FAQ
51
52For a full FAQ and more in depth details, see [the wiki page](https://github.com/clap-rs/clap/wiki/FAQ)
53
54### Comparisons
55
56First, 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!
57
58#### How does `clap` compare to [getopts](https://github.com/rust-lang-nursery/getopts)?
59
60`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.
61
62`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.
63
64Personally, 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.
65
66#### How does `clap` compare to [docopt.rs](https://github.com/docopt/docopt.rs)?
67
68I 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.
69
70`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.
71
72Because `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 far from it. This is just something to keep in mind while comparing.
73
74#### All else being equal, what are some reasons to use `clap`? (The Pitch)
75
76`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.
77
78#### All else being equal, what are some reasons *not* to use `clap`? (The Anti Pitch)
79
80Depending on the style in which you choose to define the valid arguments, `clap` can be very verbose. `clap` also offers so many fine-tuning knobs and dials, that learning everything can seem overwhelming. I strive to keep the simple cases simple, but when turning all those custom dials it can get complex. `clap` is also opinionated about parsing. Even though so much can be tweaked and tuned with `clap` (and I'm adding more all the time), there are still certain features which `clap` implements in specific ways which may be contrary to some users use-cases. Finally, `clap` is "stringly typed" when referring to arguments which can cause typos in code. This particular paper-cut is being actively worked on, and should be gone in v3.x.
81
82## Features
83
84Below 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
85
86* **Auto-generated Help, Version, and Usage information**
87 - Can optionally be fully, or partially overridden if you want a custom help, version, or usage statements
88* **Auto-generated completion scripts at compile time (Bash, Zsh, Fish, and PowerShell)**
89 - Even works through many multiple levels of subcommands
90 - Works with options which only accept certain values
91 - Works with subcommand aliases
92* **Flags / Switches** (i.e. bool fields)
93 - Both short and long versions supported (i.e. `-f` and `--flag` respectively)
94 - Supports combining short versions (i.e. `-fBgoZ` is the same as `-f -B -g -o -Z`)
95 - Supports multiple occurrences (i.e. `-vvv` or `-v -v -v`)
96* **Positional Arguments** (i.e. those which are based off an index from the program name)
97 - Supports multiple values (i.e. `myprog <file>...` such as `myprog file1.txt file2.txt` being two values for the same "file" argument)
98 - Supports Specific Value Sets (See below)
99 - Can set value parameters (such as the minimum number of values, the maximum number of values, or the exact number of values)
100 - Can set custom validations on values to extend the argument parsing capability to truly custom domains
101* **Option Arguments** (i.e. those that take values)
102 - Both short and long versions supported (i.e. `-o value`, `-ovalue`, `-o=value` and `--option value` or `--option=value` respectively)
103 - Supports multiple values (i.e. `-o <val1> -o <val2>` or `-o <val1> <val2>`)
104 - Supports delimited values (i.e. `-o=val1,val2,val3`, can also change the delimiter)
105 - Supports Specific Value Sets (See below)
106 - Supports named values so that the usage/help info appears as `-o <FILE> <INTERFACE>` etc. for when you require specific multiple values
107 - Can set value parameters (such as the minimum number of values, the maximum number of values, or the exact number of values)
108 - Can set custom validations on values to extend the argument parsing capability to truly custom domains
109* **Sub-Commands** (i.e. `git add <file>` where `add` is a sub-command of `git`)
110 - Support their own sub-arguments, and sub-sub-commands independent of the parent
111 - Get their own auto-generated Help, Version, and Usage independent of parent
112* **Support for building CLIs from YAML** - This keeps your Rust source nice and tidy and makes supporting localized translation very simple!
113* **Requirement Rules**: Arguments can define the following types of requirement rules
114 - Can be required by default
115 - Can be required only if certain arguments are present
116 - Can require other arguments to be present
117 - Can be required only if certain values of other arguments are used
118* **Confliction Rules**: Arguments can optionally define the following types of exclusion rules
119 - Can be disallowed when certain arguments are present
120 - Can disallow use of other arguments when present
121* **Groups**: Arguments can be made part of a group
122 - 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
123* **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`)
124* **Default Values**
125 - Also supports conditional default values (i.e. a default which only applies if specific arguments are used, or specific values of those arguments)
126* **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)
127* **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
128* **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')
129* **Colorized Errors (Non Windows OS only)**: Error message are printed in in colored text (this feature can optionally be disabled, see 'Optional Dependencies / Features').
130* **Global Arguments**: Arguments can optionally be defined once, and be available to all child subcommands. There values will also be propagated up/down throughout all subcommands.
131* **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.
132* **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)!)
133* Supports the Unix `--` meaning, only positional arguments follow
134
135## Quick Example
136
137The 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).
138
139 **NOTE:** All of these examples are functionally the same, but show different styles in which to use `clap`. These different styles are purely a matter of personal preference.
140
141The first example shows a method using the 'Builder Pattern' which allows more advanced configuration options (not shown in this small example), or even dynamically generating arguments when desired.
142
143```rust
144// (Full example with detailed comments in examples/01b_quick_example.rs)
145//
146// This example demonstrates clap's full 'builder pattern' style of creating arguments which is
147// more verbose, but allows easier editing, and at times more advanced options, or the possibility
148// to generate arguments dynamically.
149extern crate clap;
150use clap::{Arg, App, SubCommand};
151
152fn main() {
153 let matches = App::new("My Super Program")
154 .version("1.0")
155 .author("Kevin K. <kbknapp@gmail.com>")
156 .about("Does awesome things")
157 .arg(Arg::with_name("config")
158 .short("c")
159 .long("config")
160 .value_name("FILE")
161 .help("Sets a custom config file")
162 .takes_value(true))
163 .arg(Arg::with_name("INPUT")
164 .help("Sets the input file to use")
165 .required(true)
166 .index(1))
167 .arg(Arg::with_name("v")
168 .short("v")
169 .multiple(true)
170 .help("Sets the level of verbosity"))
171 .subcommand(SubCommand::with_name("test")
172 .about("controls testing features")
173 .version("1.3")
174 .author("Someone E. <someone_else@other.com>")
175 .arg(Arg::with_name("debug")
176 .short("d")
177 .help("print debug information verbosely")))
178 .get_matches();
179
180 // Gets a value for config if supplied by user, or defaults to "default.conf"
181 let config = matches.value_of("config").unwrap_or("default.conf");
182 println!("Value for config: {}", config);
183
184 // Calling .unwrap() is safe here because "INPUT" is required (if "INPUT" wasn't
185 // required we could have used an 'if let' to conditionally get the value)
186 println!("Using input file: {}", matches.value_of("INPUT").unwrap());
187
188 // Vary the output based on how many times the user used the "verbose" flag
189 // (i.e. 'myprog -v -v -v' or 'myprog -vvv' vs 'myprog -v'
190 match matches.occurrences_of("v") {
191 0 => println!("No verbose info"),
192 1 => println!("Some verbose info"),
193 2 => println!("Tons of verbose info"),
194 3 | _ => println!("Don't be crazy"),
195 }
196
197 // You can handle information about subcommands by requesting their matches by name
198 // (as below), requesting just the name used, or both at the same time
199 if let Some(matches) = matches.subcommand_matches("test") {
200 if matches.is_present("debug") {
201 println!("Printing debug info...");
202 } else {
203 println!("Printing normally...");
204 }
205 }
206
207 // more program logic goes here...
208}
209```
210
211One could also optionally declare their CLI in YAML format and keep your Rust source tidy
212or support multiple localized translations by having different YAML files for each localization.
213
214First, create the `cli.yml` file to hold your CLI options, but it could be called anything we like:
215
216```yaml
217name: myapp
218version: "1.0"
219author: Kevin K. <kbknapp@gmail.com>
220about: Does awesome things
221args:
222 - config:
223 short: c
224 long: config
225 value_name: FILE
226 help: Sets a custom config file
227 takes_value: true
228 - INPUT:
229 help: Sets the input file to use
230 required: true
231 index: 1
232 - verbose:
233 short: v
234 multiple: true
235 help: Sets the level of verbosity
236subcommands:
237 - test:
238 about: controls testing features
239 version: "1.3"
240 author: Someone E. <someone_else@other.com>
241 args:
242 - debug:
243 short: d
244 help: print debug information
245```
246
247Since 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:
248
249Simply change your `clap = "2.33"` to `clap = {version = "2.33", features = ["yaml"]}`.
250
251Finally we create our `main.rs` file just like we would have with the previous two examples:
252
253```rust
254// (Full example with detailed comments in examples/17_yaml.rs)
255//
256// This example demonstrates clap's building from YAML style of creating arguments which is far
257// more clean, but takes a very small performance hit compared to the other two methods.
258#[macro_use]
259extern crate clap;
260use clap::App;
261
262fn main() {
263 // The YAML file is found relative to the current file, similar to how modules are found
264 let yaml = load_yaml!("cli.yml");
265 let matches = App::from_yaml(yaml).get_matches();
266
267 // Same as previous examples...
268}
269```
270
271If 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
272
273```sh
274$ myprog --help
275My Super Program 1.0
276Kevin K. <kbknapp@gmail.com>
277Does awesome things
278
279USAGE:
280 MyApp [FLAGS] [OPTIONS] <INPUT> [SUBCOMMAND]
281
282FLAGS:
283 -h, --help Prints help information
284 -v Sets the level of verbosity
285 -V, --version Prints version information
286
287OPTIONS:
288 -c, --config <FILE> Sets a custom config file
289
290ARGS:
291 INPUT The input file to use
292
293SUBCOMMANDS:
294 help Prints this message or the help of the given subcommand(s)
295 test Controls testing features
296```
297
298**NOTE:** You could also run `myapp test --help` or `myapp help test` to see the help message for the `test` subcommand.
299
300There are also two other methods to create CLIs. Which style you choose is largely a matter of personal preference. The two other methods are:
301
302* Using [usage strings (examples/01a_quick_example.rs)](examples/01a_quick_example.rs) similar to (but not exact) docopt style usage statements. This is far less verbose than the above methods, but incurs a slight runtime penalty.
303* Using [a macro (examples/01c_quick_example.rs)](examples/01c_quick_example.rs) which is like a hybrid of the builder and usage string style. It's less verbose, but doesn't incur the runtime penalty of the usage string style. The downside is that it's harder to debug, and more opaque.
304
305Examples of each method can be found in the [examples/](examples) directory of this repository.
306
307## Try it!
308
309### Pre-Built Test
310
311To try out the pre-built examples, use the following steps:
312
313* Clone the repository `$ git clone https://github.com/clap-rs/clap && cd clap-rs/`
314* Compile the example `$ cargo build --example <EXAMPLE>`
315* Run the help info `$ ./target/debug/examples/<EXAMPLE> --help`
316* Play with the arguments!
317* You can also do a onetime run via `$ cargo run --example <EXAMPLE> -- [args to example]`
318
319### BYOB (Build Your Own Binary)
320
321To test out `clap`'s default auto-generated help/version follow these steps:
322* Create a new cargo project `$ cargo new fake --bin && cd fake`
323* Add `clap` to your `Cargo.toml`
324
325```toml
326[dependencies]
327clap = "2"
328```
329
330* Add the following to your `src/main.rs`
331
332```rust
333extern crate clap;
334use clap::App;
335
336fn main() {
337 App::new("fake").version("v1.0-beta").get_matches();
338}
339```
340
341* Build your program `$ cargo build --release`
342* Run with help or version `$ ./target/release/fake --help` or `$ ./target/release/fake --version`
343
344## Usage
345
346For full usage, add `clap` as a dependency in your `Cargo.toml` () to use from crates.io:
347
348```toml
349[dependencies]
350clap = "~2.33"
351```
352
353(**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))
354
355Then add `extern crate clap;` to your crate root.
356
357Define a list of valid arguments for your program (see the [documentation](https://docs.rs/clap/) or [examples/](examples) directory of this repo)
358
359Then run `cargo build` or `cargo update && cargo build` for your project.
360
361### Optional Dependencies / Features
362
363#### Features enabled by default
364
365* **"suggestions"**: Turns on the `Did you mean '--myoption'?` feature for when users make typos. (builds dependency `strsim`)
366* **"color"**: Turns on colored error messages. This feature only works on non-Windows OSs. (builds dependency `ansi-term` only on non-Windows targets)
367* **"vec_map"**: Use [`VecMap`](https://crates.io/crates/vec_map) internally instead of a [`BTreeMap`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html). This feature provides a _slight_ performance improvement. (builds dependency `vec_map`)
368
369To disable these, add this to your `Cargo.toml`:
370
371```toml
372[dependencies.clap]
373version = "2.33"
374default-features = false
375```
376
377You can also selectively enable only the features you'd like to include, by adding:
378
379```toml
380[dependencies.clap]
381version = "2.33"
382default-features = false
383
384# Cherry-pick the features you'd like to use
385features = [ "suggestions", "color" ]
386```
387
388#### Opt-in features
389
390* **"yaml"**: Enables building CLIs from YAML documents. (builds dependency `yaml-rust`)
391* **"unstable"**: Enables unstable `clap` features that may change from release to release
392* **"wrap_help"**: Turns on the help text wrapping feature, based on the terminal size. (builds dependency `term-size`)
393
394### Dependencies Tree
395
396The following graphic depicts `clap`s dependency graph (generated using [cargo-graph](https://github.com/kbknapp/cargo-graph)).
397
398 * **Dashed** Line: Optional dependency
399 * **Red** Color: **NOT** included by default (must use cargo `features` to enable)
400 * **Blue** Color: Dev dependency, only used while developing.
401
402
403
404### More Information
405
406You can find complete documentation on the [docs.rs](https://docs.rs/clap/) for this project.
407
408You can also find usage examples in the [examples/](examples) directory of this repo.
409
410#### Video Tutorials
411
412There's also the video tutorial series [Argument Parsing with Rust v2](https://www.youtube.com/playlist?list=PLza5oFLQGTl2Z5T8g1pRkIynR3E0_pc7U).
413
414These videos slowly trickle out as I finish them and currently a work in progress.
415
416## How to Contribute
417
418Details on how to contribute can be found in the [CONTRIBUTING.md](.github/CONTRIBUTING.md) file.
419
420### Compatibility Policy
421
422Because `clap` takes SemVer and compatibility seriously, this is the official policy regarding breaking changes and minimum required versions of Rust.
423
424`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.
425
426In order to keep from being surprised 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:
427
428```toml
429[dependencies]
430clap = "~2.33"
431```
432
433This 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.
434
435#### Warning about '~' Dependencies
436
437Using `~` can cause issues in certain circumstances.
438
439From @alexcrichton:
440
441Right now Cargo's version resolution is pretty naive, it's just a brute-force search of the solution space, returning the first resolvable graph. This also means that it currently won't terminate until it proves there is not possible resolvable graph. This leads to situations where workspaces with multiple binaries, for example, have two different dependencies such as:
442
443```toml,no_sync
444
445# In one Cargo.toml
446[dependencies]
447clap = "~2.33.0"
448
449# In another Cargo.toml
450[dependencies]
451clap = "2.33.0"
452```
453
454This is inherently an unresolvable crate graph in Cargo right now. Cargo requires there's only one major version of a crate, and being in the same workspace these two crates must share a version. This is impossible in this location, though, as these version constraints cannot be met.
455
456#### Minimum Version of Rust
457
458`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 1.41.0, meaning `clap` is guaranteed to compile with 1.39.0 and beyond.
459
460At the 1.42.0 stable release, `clap` will be guaranteed to compile with 1.40.0 and beyond, etc.
461
462Upon bumping the minimum version of Rust (assuming it's within the stable-2 range), it *must* be clearly annotated in the `CHANGELOG.md`
463
464#### Breaking Changes
465
466`clap` takes a similar policy to Rust and will bump the major version number upon breaking changes with only the following exceptions:
467
468 * The breaking change is to fix a security concern
469 * The breaking change is to be fixing a bug (i.e. relying on a bug as a feature)
470 * The breaking change is a feature isn't used in the wild, or all users of said feature have given approval *prior* to the change
471
472#### Compatibility with Wasm
473
474A best effort is made to ensure that `clap` will work on projects targeting `wasm32-unknown-unknown`. However there is no dedicated CI build
475covering this specific target.
476
477## License
478
479`clap` is licensed under the MIT license. Please read the [LICENSE-MIT](LICENSE-MIT) file in this repository for more information.
480
481## Related Crates
482
483There are several excellent crates which can be used with `clap`, I recommend checking them all out! If you've got a crate that would be a good fit to be used with `clap` open an issue and let me know, I'd love to add it!
484
485* [`structopt`](https://github.com/TeXitoi/structopt) - This crate allows you to define a struct, and build a CLI from it! No more "stringly typed" and it uses `clap` behind the scenes! (*Note*: There is work underway to pull this crate into mainline `clap`).
486* [`assert_cli`](https://github.com/assert-rs/assert_cli) - This crate allows you test your CLIs in a very intuitive and functional way!
487
488## Recent Breaking Changes
489
490`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).
491
492As of 2.27.0:
493
494* Argument values now take precedence over subcommand names. This only arises by using unrestrained multiple values and subcommands together where the subcommand name can coincide with one of the multiple values. Such as `$ prog <files>... <subcommand>`. The fix is to place restraints on number of values, or disallow the use of `$ prog <prog-args> <subcommand>` structure.
495
496As of 2.0.0 (From 1.x)
497
498* **Fewer lifetimes! Yay!**
499 * `App<'a, 'b, 'c, 'd, 'e, 'f>` => `App<'a, 'b>`
500 * `Arg<'a, 'b, 'c, 'd, 'e, 'f>` => `Arg<'a, 'b>`
501 * `ArgMatches<'a, 'b>` => `ArgMatches<'a>`
502* **Simply Renamed**
503 * `App::arg_group` => `App::group`
504 * `App::arg_groups` => `App::groups`
505 * `ArgGroup::add` => `ArgGroup::arg`
506 * `ArgGroup::add_all` => `ArgGroup::args`
507 * `ClapError` => `Error`
508 * struct field `ClapError::error_type` => `Error::kind`
509 * `ClapResult` => `Result`
510 * `ClapErrorType` => `ErrorKind`
511* **Removed Deprecated Functions and Methods**
512 * `App::subcommands_negate_reqs`
513 * `App::subcommand_required`
514 * `App::arg_required_else_help`
515 * `App::global_version(bool)`
516 * `App::versionless_subcommands`
517 * `App::unified_help_messages`
518 * `App::wait_on_error`
519 * `App::subcommand_required_else_help`
520 * `SubCommand::new`
521 * `App::error_on_no_subcommand`
522 * `Arg::new`
523 * `Arg::mutually_excludes`
524 * `Arg::mutually_excludes_all`
525 * `Arg::mutually_overrides_with`
526 * `simple_enum!`
527* **Renamed Error Variants**
528 * `InvalidUnicode` => `InvalidUtf8`
529 * `InvalidArgument` => `UnknownArgument`
530* **Usage Parser**
531 * Value names can now be specified inline, i.e. `-o, --option <FILE> <FILE2> 'some option which takes two files'`
532 * **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**
533* `ArgMatches::values_of` returns an `Values` now which implements `Iterator` (should not break any code)
534* `crate_version!` returns `&'static str` instead of `String`
535
536### Deprecations
537
538Old method names will be left around for several minor version bumps, or one major version bump.
539
540As of 2.27.0:
541
542* **AppSettings::PropagateGlobalValuesDown:** this setting deprecated and is no longer required to propagate values down or up
543
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
){kind=link}
