clap

Linux: Windows:

Command Line Argument Parser for Rust

It is a simple-to-use, efficient, and full-featured library for parsing command line arguments and subcommands when writing console/terminal applications.

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Table of Contents

• What's New
• About
• FAQ
• Features
• Quick Example
• Try it!
  • Pre-Built Test
  • BYOB (Build Your Own Binary)
• Usage
  • Optional Dependencies / Features
  • Dependencies Tree
  • More Information
    • Video Tutorials
• How to Contribute
  • Running the tests
  • Goals
• License
• Recent Breaking Changes
  • Deprecations

Created by gh-md-toc

What's New

Here's what's new in v2.18.0

• Completions: Adds completion support for Microsoft PowerShell! (Thanks to @Arnavion)

Here's what's new in v2.17.1

• Fixes a bug where using low index multiples was propagated to subcommands

Here's what's new in v2.17.0

• Allows specifying the second to last positional argument as multiple(true) (i.e. things such as mv <files>... <target>)
• Adds an App::get_name and App::get_bin_name

Here's what's new in v2.16.4

• Fixes bug that caused panic on subcommands with aliases
• Conflicting argument errors are now symetrical, meaning more consistent and better usage suggestions
• Fixes typo in example 13a_enum_values_automatic
• Fixes failing yaml example (#715)
• Fixes the debug feature (#716)

Here's the highlights for v2.16.3

• Fixes a bug where the derived display order isn't propagated
• yaml-example: fixes some inconsistent args in the example

Here's the highlights for v2.16.2

• Fixes a bug where single quotes are not escaped

Here's the highlights for v2.16.1

• Help Message: fixes a regression bug where args with multiple(true) threw off alignment

Here's the highlights for v2.16.0

• Completions: adds automatic ZSH completion script generation support! 🎉 🎉

Here's a gif of them in action!

Here's the highlights for v2.15.0

• AppSettings: adds new setting AppSettings::AllowNegativeNumbers which functions like AllowLeadingHyphen except only allows undefined negative numbers to pass parsing.
• Improves some of the documentation of AppSettings by moving variants into roughly alphabetical order

Here's the highlights for v2.14.1 (Huge thanks to all the contributors who put in a lot of work this cycle! Especially @tormol @nabijaczleweli and @wdv4758h)

• Stabilize clap_app! macro (i.e. no longer need to use unstable feature)
• Fixes a bug that made determining when to auto-wrap long help messages inconsistent
• Fixes fish completions for nested subcommands
• Improve documentation around features
• Reword docs for ErrorKind and App::settings
• Fix tests that fail when the suggestions feature is disabled
• Fix the OsString-using doc-tests
• Tag non-rust code blocks as such instead of ignoring them
• Improve some errors about subcommands
• Makes sure the doc-tests don't fail before "missing file" in YAML tests
• Deprecate App::with_defaults
• Make lints not enable other nightly-requiring features

Here's the highlights for v2.14.0

• One can now alias arguments either visibly (whichc appears in the help text) or invisibly just like subcommands!
• The from_usage parser now correctly handles non-ascii names / options and help!
• Fixes a bug in the require_delimiter code which caused some incorrect parses
• Fixes various typos in the docs
• Various other small performance improvements and enhancements

Here's the highlights for v2.13.0

• Value Delimiters: fixes the confusion around implicitly setting value delimiters. (The default is to not use a delimiter unless explicitly set)
• Docs: Updates README.md with new website information and updated video tutorials info
• Docs: Updates the docs about removing implicit value_delimiter(true)
• Docs: Adds better examples on using default values

Here's the highlights for v2.12.1

• Fixes a regression-bug where the old {n} newline char stopped being replaced a properly re-aligned newline

Here's the highlights for v2.12.0

• 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
• Updates the docs for the Arg::multiple method WRT value delimiters and default settings
• 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)
• Removes some redundant contains() checks for minor performance improvements
• Fixes a bug where valid args aren't recognized with the AppSettings::AllowLeadingHyphen setting
• clap now ignores hard newlines in help messages and properly re-aligns text, but still wraps if the term width is too small
• Makes some minor changes to when next line help is automatically used
• Adds support for the setting Arg::require_delimiter from YAML
• Removes the verbage about using '{n}' to insert newlines in help text from the docs (the normal \n can now be used)
• Documents AppSetting::DisableVersion

Here's the highlights for v2.11.3

• clap no longer requires one to use {n} inside help text to insert a newline that is properly aligned. One can now use the normal \n.
• clap now ignores hard newlines in help messages and properly re-aligns text, but still wraps if the term width is too small
• Supports setting Arg::require_delimiter from YAML

Here's the highlights for v2.11.2

• Makes some minor changes to when next line help is automatically used for improved wrapping

Here's the highlights for v2.11.1

• Fixes an issue where settings weren't propogated down through grand-child subcommands
• Errors can now have custom description
• Uses term_size instead of home-grown solution on Windows
• Updates deps with some minor bug fixes

Here's the highlights for v2.11.0

• Adds the ability to wrap help text intelligently on Windows!
• Moves docs to docs.rs!
• Fixes some usage strings that contain both args in groups and ones that conflict with each other
• Uses standard conventions for bash completion files, namely {bin}.bash-completion
• Automatically moves help text to the next line and wraps when term width is determined to be too small, or help text is too long
• Vastly improves development error messages when using YAML
• Adds App::with_defaults to automatically use crate_authors! and crate_version! macros
• Other minor improvements and bug fixes

Here's the highlights for v2.10.4

• Fixes a bug where help is wrapped incorrectly and causing a panic with some non-English characters

Here's the highlights for v2.10.3

• Fixes a bug with non-English characters in help text wrapping, where the character is stripped or causes a panic
• Fixes an issue with strsim which caused a panic in some scenarios
• Adds a shorthand way to ignore help text wrapping and use source formatting (i.e. App::set_term_width(0))

Here's the highlights for v2.10.2

• Fixes a critical bug where the help message is printed twice

Here's the highlights for v2.10.1

• Help Subcommand: fixes misleading usage string when using multi-level subcommmands such as myprog help subcmd1 subcmd2
• YAML: allows using lists or single values with certain arg declarations for increased ergonomics

Here's the highlights for v2.10.0

• Fish Shell Completions: one can generate a basic fish completions script at compile time!
• External SubCommands: fixes a bug which now correctly preserves external subcommand name along with args to said command (Minor breaking change that breaks no known real world code)
• YAML Documentation: fixes example 17's incorrect reference to arg_groups instead of groups

Here's the highlights for v2.9.3

• Adds the ability to generate completions to an io::Write object
• Adds an App::unset_setting and App::unset_settings
• Fixes bug where only first arg in list of required_unless_one is recognized
• Fixes a typo bug SubcommandsRequired->SubcommandRequired

Here's the highlights for v2.9.2

• fixes bug where --help and --version short weren't added to the completion list
• improves completions allowing multiple bins to have seperate completion files

Here's the highlights for v2.9.0

• Completions: one can now generate a bash completions script at compile time! These completions work with options using possible values, subcommand aliases, and even multiple levels of subcommands
• Minor bug fixes when using AppSettings::TrailingVarArg and AppSettings::AllowLeadingHyphen

Here's the highlights for v2.8.0

• Arg: adds new optional setting Arg::require_delimiter which requires val delimiter to parse multiple values
• The terminal sizing portion has been factored out into a separate crate, term_size
• Minor bug fixes

Here's the highlights for v2.7.1

• Options:
  • 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)

Here's the highlights for v2.7.0

• Usage Strings: [FLAGS] and [ARGS] are no longer blindly added to usage strings, instead only when applicable
• arg_enum!: allows using more than one meta item, or things like #[repr(C)] with arg_enum!s
• App::print_help: now prints the same as would have been printed by --help or the like
• Help Messages:
• prevents invoking <cmd> help help and displaying incorrect help message
• subcommand help messages requested via <cmd> help <sub> now correctly match <cmd> <sub> --help
• ArgGroups:
• one can now specify groups which require AT LEAST one of the args
• allows adding multiple ArgGroups per Arg
• Documentation: vastly improves ArgGroup docs by adding better examples
• Documentation: fixes a bunch of typos in the documentation

Here's the highlights for v2.6.0

• Global Settings: One can now set an AppSetting which is propogated down through child subcommands
• Terminal Wrapping: Allows wrapping at specified term width (Even on Windows!) (can now set an absolute width to "smart" wrap at)
• SubCommands/Aliases: adds support for visible aliases for subcommands (i.e. aliases that are dipslayed in the help message)
• Subcommands/Aliases: when viewing the help of an alias, it now display help of the aliased subcommand
• Improves the default usage string when only a single positional arg is present
• Adds new setting to stop delimiting values with -- or AppSettings::TrailingVarArg
• App::before_help and App::after_help now correctly wrap
• Fixes bug where positional args are printed out of order when using templates
• Fixes bug where one can't override the auto-generated version or help flags
• Fixes issue where App::before_help wasn't printed
• Fixes a failing windows build
• Fixes bug where new color settings couldn't be converted from strings
• Adds missing YAML methods for App and Arg
• Allows printing version to any io::Write object
• Removes extra newline from help and version output

Here's what's new in v.2.5.2

• Removes trailing newlines from help and version output
• Allows printing version to any io::Write object
• Inter-links all types and pages
• Makes all publicly available types viewable in docs
• Fixes bug where one can't override version or help flags
• Fixes bug where args are printed out of order when using templates
• Fixes issue where App::before_help wasn't printed properly

Here's what's new in v.2.5.0

• Subcommands now support aliases - think of them as hidden subcommands that dispatch to said subcommand automatically

Here's what's new in v2.4.3

• Bug Fixes
• Usage strings get de-deuplicated when there are args which are also part ``ArgGroups
• Fixed times when ArgGroups are duplicated in usage strings
• Improvements
• Positional arguments which are part of a group are now formatted in a more readable way (fewer brackets)
• Positional arguments use the standard <> brackets to reduce confusion
• The default help string for the help subcommand has been shortened to fit in 80 columns

Here's the highlights from v2.4.0

• Before Help: adds support for displaying info before help message
• Required Unless: adds support for allowing args that are required unless certain other args are present
• Bug fixes

Here's the highlights from v2.3.0

• New Help Template Engine!: Now you have full control over the layout of your help message. Major thanks to @hgrecco
• 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
• Colored Help Messages: Help messages can now be optionally colored (See the AppSettings::ColoredHelp setting). Screenshot below.
• A bunch of bug fixes

Here's the highlights from v2.2.1

• 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.
• Bug fixes

An example of the optional colored help:

Here's the highlights from v2.2.0

• 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.)

• Other minor bug fixes

An example of the help text wrapping at term width:

In v2.1.2

• 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
• Documentation Examples: The examples in the documentation have been vastly improved

For full details, see CHANGELOG.md

About

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.

FAQ

For a full FAQ and more in depth details, see the wiki page

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?

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.

How does clap compare to docopt.rs?

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.

All else being equal, what are some reasons to use clap?

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.

Features

Below are a few of the features which clap supports, full descriptions and usage can be found in the documentation and examples/ directory

• Auto-generated Help, Version, and Usage information
  • Can optionally be fully, or partially overridden if you want a custom help, version, or usage
• Auto-generated bash completion scripts at compile time
  • Even works through many multiple levels of subcommands
  • Works with options which only accept certain values
  • Works with subcommand aliases
• Flags / Switches (i.e. bool fields)
  • Both short and long versions supported (i.e. -f and --flag respectively)
  • Supports combining short versions (i.e. -fBgoZ is the same as -f -B -g -o -Z)
  • Supports multiple occurrences (i.e. -vvv or -v -v -v)
• Positional Arguments (i.e. those which are based off an index from the program name)
  • Supports multiple values (i.e. myprog <file>... such as myprog file1.txt file2.txt being two values for the same "file" argument)
  • Supports Specific Value Sets (See below)
  • Can set value parameters (such as the minimum number of values, the maximum number of values, or the exact number of values)
  • Can set custom validations on values to extend the argument parsing capability to truly custom domains
• Option Arguments (i.e. those that take values)
  • Both short and long versions supported (i.e. -o value, -ovalue, -o=value and --option value or --option=value respectively)
  • Supports multiple values (i.e. -o <val1> -o <val2> or -o <val1> <val2>)
  • Supports delimited values (i.e. -o=val1,val2,val3, can also change the delimiter)
  • Supports Specific Value Sets (See below)
  • Supports named values so that the usage/help info appears as -o <FILE> <INTERFACE> etc. for when you require specific multiple values
  • Can set value parameters (such as the minimum number of values, the maximum number of values, or the exact number of values)
  • Can set custom validations on values to extend the argument parsing capability to truly custom domains
• Sub-Commands (i.e. git add <file> where add is a sub-command of git)
  • Support their own sub-arguments, and sub-sub-commands independent of the parent
  • Get their own auto-generated Help, Version, and Usage independent of parent
• Support for building CLIs from YAML - This keeps your Rust source nice and tidy and makes supporting localized translation very simple!
• Requirement Rules: Arguments can define the following types of requirement rules
  • Can be required by default
  • Can be required only if certain arguments are present
  • Can require other arguments to be present
• Confliction 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
• 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
• 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 for how to do this (Thanks to 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. You can also use claps arg_enum! macro to create an enum with variants that automatically implement std::str::FromStr. See 13a_enum_values_automatic example 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 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').
• Global Arguments: Arguments can optionally be defined once, and be available to all child subcommands.
• 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!)
• Supports the Unix -- meaning, only positional arguments follow

Quick Example

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, examples/ directory of this repository or the video tutorials.

NOTE: All these examples are functionally the same, but show three different styles in which to use clap

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.

// (Full example with detailed comments in examples/01b_quick_example.rs)
//
// This example demonstrates clap's full 'builder pattern' style of creating arguments which is
// more verbose, but allows easier editing, and at times more advanced options, or the possibility
// to generate arguments dynamically.
extern crate clap;
use clap::{Arg, App, SubCommand};

fn main() {
    let matches = App::new("My Super Program")
                          .version("1.0")
                          .author("Kevin K. <kbknapp@gmail.com>")
                          .about("Does awesome things")
                          .arg(Arg::with_name("config")
                               .short("c")
                               .long("config")
                               .value_name("FILE")
                               .help("Sets a custom config file")
                               .takes_value(true))
                          .arg(Arg::with_name("INPUT")
                               .help("Sets the input file to use")
                               .required(true)
                               .index(1))
                          .arg(Arg::with_name("v")
                               .short("v")
                               .multiple(true)
                               .help("Sets the level of verbosity"))
                          .subcommand(SubCommand::with_name("test")
                                      .about("controls testing features")
                                      .version("1.3")
                                      .author("Someone E. <someone_else@other.com>")
                                      .arg(Arg::with_name("debug")
                                          .short("d")
                                          .help("print debug information verbosely")))
                          .get_matches();

    // Gets a value for config if supplied by user, or defaults to "default.conf"
    let config = matches.value_of("config").unwrap_or("default.conf");
    println!("Value for config: {}", config);

    // Calling .unwrap() is safe here because "INPUT" is required (if "INPUT" wasn't
    // required we could have used an 'if let' to conditionally get the value)
    println!("Using input file: {}", matches.value_of("INPUT").unwrap());

    // Vary the output based on how many times the user used the "verbose" flag
    // (i.e. 'myprog -v -v -v' or 'myprog -vvv' vs 'myprog -v'
    match matches.occurrences_of("v") {
        0 => println!("No verbose info"),
        1 => println!("Some verbose info"),
        2 => println!("Tons of verbose info"),
        3 | _ => println!("Don't be crazy"),
    }

    // You can handle information about subcommands by requesting their matches by name
    // (as below), requesting just the name used, or both at the same time
    if let Some(matches) = matches.subcommand_matches("test") {
        if matches.is_present("debug") {
            println!("Printing debug info...");
        } else {
            println!("Printing normally...");
        }
    }

    // more program logic goes here...
}

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).

// (Full example with detailed comments in examples/01a_quick_example.rs)
//
// This example demonstrates clap's "usage strings" method of creating arguments
// which is less verbose
extern crate clap;
use clap::{Arg, App, SubCommand};

fn main() {
    let matches = App::new("myapp")
                          .version("1.0")
                          .author("Kevin K. <kbknapp@gmail.com>")
                          .about("Does awesome things")
                          .args_from_usage(
                              "-c, --config=[FILE] 'Sets a custom config file'
                              <INPUT>              'Sets the input file to use'
                              -v...                'Sets the level of verbosity'")
                          .subcommand(SubCommand::with_name("test")
                                      .about("controls testing features")
                                      .version("1.3")
                                      .author("Someone E. <someone_else@other.com>")
                                      .arg_from_usage("-d, --debug 'Print debug information'"))
                          .get_matches();

    // Same as previous 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):

name: myapp
version: "1.0"
author: Kevin K. <kbknapp@gmail.com>
about: Does awesome things
args:
    - config:
        short: c
        long: config
        value_name: FILE
        help: Sets a custom config file
        takes_value: true
    - INPUT:
        help: Sets the input file to use
        required: true
        index: 1
    - verbose:
        short: v
        multiple: true
        help: Sets the level of verbosity
subcommands:
    - test:
        about: controls testing features
        version: "1.3"
        author: Someone E. <someone_else@other.com>
        args:
            - debug:
                short: d
                help: print debug information

Since this feature is not compiled in by default we need to enable a feature flag in Cargo.toml: Simply change your clap = "2" to clap = {version = "2", features = ["yaml"]}.

At last we create our main.rs file just like we would have with the previous two examples:

// (Full example with detailed comments in examples/17_yaml.rs)
//
// This example demonstrates clap's building from YAML style of creating arguments which is far
// more clean, but takes a very small performance hit compared to the other two methods.
#[macro_use]
extern crate clap;
use clap::App;

fn main() {
    // The YAML file is found relative to the current file, similar to how modules are found
    let yaml = load_yaml!("cli.yml");
    let matches = App::from_yaml(yaml).get_matches();

    // Same as previous examples...
}

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

$ myprog --help
My Super Program 1.0
Kevin K. <kbknapp@gmail.com>
Does awesome things

USAGE:
    MyApp [FLAGS] [OPTIONS] <INPUT> [SUBCOMMAND]

FLAGS:
    -h, --help       Prints this message
    -v               Sets the level of verbosity
    -V, --version    Prints version information

OPTIONS:
    -c, --config <FILE>    Sets a custom config file

ARGS:
    INPUT    The input file to use

SUBCOMMANDS:
    help    Prints this message
    test    Controls testing features

NOTE: You could also run myapp test --help to see similar output and options for the test subcommand.

Try it!

Pre-Built Test

To try out the pre-built example, use the following steps:

• Clone the repository $ git clone https://github.com/kbknapp/clap-rs && cd clap-rs/tests
• Compile the example $ cargo build --release
• Run the help info $ ./target/release/claptests --help
• Play with the arguments!

BYOB (Build Your Own Binary)

To test out clap's default auto-generated help/version follow these steps:

• Create a new cargo project $ cargo new fake --bin && cd fake
• Add clap to your Cargo.toml

[dependencies]
clap = "2"

• Add the following to your src/main.rs

extern crate clap;
use clap::App;

fn main() {
  App::new("fake").version("v1.0-beta").get_matches();
}

• Build your program $ cargo build --release
• Run with help or version $ ./target/release/fake --help or $ ./target/release/fake --version

Usage

For full usage, add clap as a dependency in your Cargo.toml file to use from crates.io:

[dependencies]
clap = "2"

Or get the latest changes from the master branch at github:

[dependencies.clap]
git = "https://github.com/kbknapp/clap-rs.git"

Add extern crate clap; to your crate root.

Define a list of valid arguments for your program (see the documentation or examples/ directory of this repo)

Then run cargo build or cargo update && cargo build for your project.

Optional Dependencies / Features

Features enabled by default

• "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 and libc)
• "wrap_help": Wraps the help at the actual terminal width when available, instead of 120 chracters. (builds dependency term_size, and libc)

To disable these, add this to your Cargo.toml:

[dependencies.clap]
version = "2"
default-features = false

You can also selectively enable only the features you'd like to include, by adding:

[dependencies.clap]
version = "2"
default-features = false

# Cherry-pick the features you'd like to use
features = [ "suggestions", "color" ]

Opt-in features

• "yaml": Enables building CLIs from YAML documents. (builds dependency yaml-rust)

Dependencies Tree

The following graphic depicts claps dependency graph (generated using cargo-graph).

• Dashed Line: Optional dependency
• Red Color: NOT included by default (must use cargo features to enable)
• Blue Color: Dev dependency, only used while developing.

More Information

You can find complete documentation on the docs.rs for this project.

You can also find usage examples in the examples/ directory of this repo.

Video Tutorials

There's also the video tutorial series Argument Parsing with Rust v2.

These videos slowly trickle out as I finish them and currently a work in progress.

How to Contribute

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/ directory, or file an issue and tell me. I'm all about giving credit where credit is due :)

Please read CONTRIBUTING.md before you start contributing.

To test with all features both enabled and disabled, you can run theese commands:

$ cargo test --no-default-features
$ cargo test --features yaml

If you have a nightly compiler you can append --features lints to both commands to get style warnings and code smells; If you get one from code you think is fine, you can ignore it by prepending #[cfg_attr(feature="lints", allow(lint_name))] to the function or impl block.

If you are debugging (or just trying to understand the code) you can enable the "debug" feature which will trace function calls and brances in some parts of the code.

Goals

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).

• Remain backwards compatible when possible
  • If backwards compatibility must be broken, use deprecation warnings if at all possible before removing legacy code
  • This does not apply for security concerns
• Parse arguments quickly
  • Parsing of arguments shouldn't slow down usage of the main program
  • This is also true of generating help and usage information (although slightly less stringent, as the program is about to exit)
• Try to be cognizant of memory usage
  • Once parsing is complete, the memory footprint of clap should be low since the main program is the star of the show
• panic! on developer error, exit gracefully on end-user error

License

clap is licensed under the MIT license. Please read the LICENSE-MIT file in this repository for more information.

Recent Breaking Changes

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.

As of 2.0.0 (From 1.x)

• Fewer lifetimes! Yay!
• App<'a, 'b, 'c, 'd, 'e, 'f> => App<'a, 'b>
• Arg<'a, 'b, 'c, 'd, 'e, 'f> => Arg<'a, 'b>
• ArgMatches<'a, 'b> => ArgMatches<'a>
• Simply Renamed
• App::arg_group => App::group
• App::arg_groups => App::groups
• ArgGroup::add => ArgGroup::arg
• ArgGroup::add_all => ArgGroup::args
• ClapError => Error
• 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
• Using the clap_app! macro requires compiling with the unstable feature because the syntax could change slightly in the future

Deprecations

Old method names will be left around for several minor version bumps, or one major version bump.

As of 2.2.0:

• None!