# Struct clap::builder::Arg

source · [−]

    pub struct Arg { /* private fields */ }

Expand description

The abstract representation of a command line argument. Used to set all the options and relationships that define a valid argument for the program.

There are two methods for constructing `Arg`s, using the builder pattern and setting options manually, or using a usage string which is far less verbose but has fewer options. You can also use a combination of the two methods to achieve the best of both worlds.

- Basic API
- Value Handling
- Help
- Advanced Argument Relations
- Reflection

## Examples

    // Using the traditional builder pattern and setting each option manually
    let cfg = Arg::new("config")
          .short('c')
          .long("config")
          .action(ArgAction::Set)
          .value_name("FILE")
          .help("Provides a config file to myprog");
    // Using a usage string (setting a similar argument to the one above)
    let input = arg!(-i --input <FILE> "Provides an input file to the program");

## Implementations

source

### impl Arg

#### Basic API

source

#### pub fn new(id: impl Into<Id>) -> Self

Create a new `Arg` with a unique name.

The name is used to check whether or not the argument was used at runtime, get values, set relationships with other args, etc..

NOTE: In the case of arguments that take values (i.e. `Arg::action(ArgAction::Set)`) and positional arguments (i.e. those without a preceding `-` or `--`) the name will also be displayed when the user prints the usage/help information of the program.

##### Examples

    Arg::new("config")

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#### pub fn id(self, id: impl Into<Id>) -> Self

Set the identifier used for referencing this argument in the clap API.

See `Arg::new` for more details.

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#### pub fn short(self, s: impl IntoResettable<char>) -> Self

Sets the short version of the argument without the preceding `-`.

By default `V` and `h` are used by the auto-generated `version` and `help` arguments, respectively. You will need to disable the auto-generated flags (`disable_help_flag`, `disable_version_flag`) and define your own.

##### Examples

When calling `short`, use a single valid UTF-8 character which will allow using the argument via a single hyphen (`-`) such as `-c`:

    let m = Command::new("prog")
        .arg(Arg::new("config")
            .short('c')
            .action(ArgAction::Set))
        .get_matches_from(vec![
            "prog", "-c", "file.toml"
        ]);

    assert_eq!(m.get_one::<String>("config").map(String::as_str), Some("file.toml"));

To use `-h` for your own flag and still have help:

    let m = Command::new("prog")
        .disable_help_flag(true)
        .arg(Arg::new("host")
            .short('h')
            .long("host"))
        .arg(Arg::new("help")
            .long("help")
            .global(true)
            .action(ArgAction::Help))
        .get_matches_from(vec![
            "prog", "-h", "wikipedia.org"
        ]);

    assert_eq!(m.get_one::<String>("host").map(String::as_str), Some("wikipedia.org"));

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#### pub fn long(self, l: impl IntoResettable<Str>) -> Self

Sets the long version of the argument without the preceding `--`.

By default `version` and `help` are used by the auto-generated `version` and `help` arguments, respectively. You may use the word `version` or `help` for the long form of your own arguments, in which case `clap` simply will not assign those to the auto-generated `version` or `help` arguments.

NOTE: Any leading `-` characters will be stripped

##### Examples

To set `long` use a word containing valid UTF-8. If you supply a double leading `--` such as `--config` they will be stripped. Hyphens in the middle of the word, however, will not be stripped (i.e. `config-file` is allowed).

Setting `long` allows using the argument via a double hyphen (`--`) such as `--config`

    let m = Command::new("prog")
        .arg(Arg::new("cfg")
            .long("config")
            .action(ArgAction::Set))
        .get_matches_from(vec![
            "prog", "--config", "file.toml"
        ]);

    assert_eq!(m.get_one::<String>("cfg").map(String::as_str), Some("file.toml"));

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#### pub fn alias(self, name: impl IntoResettable<Str>) -> Self

Add an alias, which functions as a hidden long flag.

This is more efficient, and easier than creating multiple hidden arguments as one only needs to check for the existence of this command, and not all variants.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                .long("test")
                .alias("alias")
                .action(ArgAction::Set))
           .get_matches_from(vec![
                "prog", "--alias", "cool"
            ]);
    assert_eq!(m.get_one::<String>("test").unwrap(), "cool");

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#### pub fn short_alias(self, name: impl IntoResettable<char>) -> Self

Add an alias, which functions as a hidden short flag.

This is more efficient, and easier than creating multiple hidden arguments as one only needs to check for the existence of this command, and not all variants.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                .short('t')
                .short_alias('e')
                .action(ArgAction::Set))
           .get_matches_from(vec![
                "prog", "-e", "cool"
            ]);
    assert_eq!(m.get_one::<String>("test").unwrap(), "cool");

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#### pub fn aliases(self, names: impl IntoIterator<Item = impl Into<Str>>) -> Self

Add aliases, which function as hidden long flags.

This is more efficient, and easier than creating multiple hidden subcommands as one only needs to check for the existence of this command, and not all variants.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                        .long("test")
                        .aliases(["do-stuff", "do-tests", "tests"])
                        .action(ArgAction::SetTrue)
                        .help("the file to add")
                        .required(false))
                .get_matches_from(vec![
                    "prog", "--do-tests"
                ]);
    assert_eq!(*m.get_one::<bool>("test").expect("defaulted by clap"), true);

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#### pub fn short_aliases(self, names: impl IntoIterator<Item = char>) -> Self

Add aliases, which functions as a hidden short flag.

This is more efficient, and easier than creating multiple hidden subcommands as one only needs to check for the existence of this command, and not all variants.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                        .short('t')
                        .short_aliases(['e', 's'])
                        .action(ArgAction::SetTrue)
                        .help("the file to add")
                        .required(false))
                .get_matches_from(vec![
                    "prog", "-s"
                ]);
    assert_eq!(*m.get_one::<bool>("test").expect("defaulted by clap"), true);

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#### pub fn visible_alias(self, name: impl IntoResettable<Str>) -> Self

Add an alias, which functions as a visible long flag.

Like `Arg::alias`, except that they are visible inside the help message.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                    .visible_alias("something-awesome")
                    .long("test")
                    .action(ArgAction::Set))
           .get_matches_from(vec![
                "prog", "--something-awesome", "coffee"
            ]);
    assert_eq!(m.get_one::<String>("test").unwrap(), "coffee");

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#### pub fn visible_short_alias(self, name: impl IntoResettable<char>) -> Self

Add an alias, which functions as a visible short flag.

Like `Arg::short_alias`, except that they are visible inside the help message.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                    .long("test")
                    .visible_short_alias('t')
                    .action(ArgAction::Set))
           .get_matches_from(vec![
                "prog", "-t", "coffee"
            ]);
    assert_eq!(m.get_one::<String>("test").unwrap(), "coffee");

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#### pub fn visible_aliases(
self,
names: impl IntoIterator<Item = impl Into<Str>>
) -> Self

Add aliases, which function as visible long flags.

Like `Arg::aliases`, except that they are visible inside the help message.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                    .long("test")
                    .action(ArgAction::SetTrue)
                    .visible_aliases(["something", "awesome", "cool"]))
           .get_matches_from(vec![
                "prog", "--awesome"
            ]);
    assert_eq!(*m.get_one::<bool>("test").expect("defaulted by clap"), true);

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#### pub fn visible_short_aliases(self, names: impl IntoIterator<Item = char>) -> Self

Add aliases, which function as visible short flags.

Like `Arg::short_aliases`, except that they are visible inside the help message.

##### Examples

    let m = Command::new("prog")
                .arg(Arg::new("test")
                    .long("test")
                    .action(ArgAction::SetTrue)
                    .visible_short_aliases(['t', 'e']))
           .get_matches_from(vec![
                "prog", "-t"
            ]);
    assert_eq!(*m.get_one::<bool>("test").expect("defaulted by clap"), true);

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#### pub fn index(self, idx: impl IntoResettable<usize>) -> Self

Specifies the index of a positional argument starting at 1.

NOTE: The index refers to position according to other positional argument. It does not define position in the argument list as a whole.

NOTE: You can optionally leave off the `index` method, and the index will be assigned in order of evaluation. Utilizing the `index` method allows for setting indexes out of order

NOTE: This is only meant to be used for positional arguments and shouldn’t to be used with `Arg::short` or `Arg::long`.

NOTE: When utilized with [`Arg::num_args(1..)`], only the last positional argument may be defined as having a variable number of arguments (i.e. with the highest index)

##### Panics

`Command` will `panic!` if indexes are skipped (such as defining `index(1)` and `index(3)` but not `index(2)`, or a positional argument is defined as multiple and is not the highest index

##### Examples

    Arg::new("config")
        .index(1)

    let m = Command::new("prog")
        .arg(Arg::new("mode")
            .index(1))
        .arg(Arg::new("debug")
            .long("debug")
            .action(ArgAction::SetTrue))
        .get_matches_from(vec![
            "prog", "--debug", "fast"
        ]);

    assert!(m.contains_id("mode"));
    assert_eq!(m.get_one::<String>("mode").unwrap(), "fast"); // notice index(1) means "first positional"
                                                              // *not* first argument

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#### pub fn trailing_var_arg(self, yes: bool) -> Self

This is a “VarArg” and everything that follows should be captured by it, as if the user had used a `--`.

NOTE: To start the trailing “VarArg” on unknown flags (and not just a positional value), set `allow_hyphen_values`. Either way, users still have the option to explicitly escape ambiguous arguments with `--`.

NOTE: `Arg::value_delimiter` still applies if set.

NOTE: Setting this requires `Arg::num_args(..)`.

##### Examples

    let m = Command::new("myprog")
        .arg(arg!(<cmd> ... "commands to run").trailing_var_arg(true))
        .get_matches_from(vec!["myprog", "arg1", "-r", "val1"]);

    let trail: Vec<_> = m.get_many::<String>("cmd").unwrap().collect();
    assert_eq!(trail, ["arg1", "-r", "val1"]);

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#### pub fn last(self, yes: bool) -> Self

This arg is the last, or final, positional argument (i.e. has the highest index) and is only able to be accessed via the `--` syntax (i.e. `$ prog args -- last_arg`).

Even, if no other arguments are left to parse, if the user omits the `--` syntax they will receive an `UnknownArgument` error. Setting an argument to `.last(true)` also allows one to access this arg early using the `--` syntax. Accessing an arg early, even with the `--` syntax is otherwise not possible.

NOTE: This will change the usage string to look like `$ prog [OPTIONS] [-- <ARG>]` if `ARG` is marked as `.last(true)`.

NOTE: This setting will imply `crate::Command::dont_collapse_args_in_usage` because failing to set this can make the usage string very confusing.

NOTE: This setting only applies to positional arguments, and has no effect on OPTIONS

NOTE: Setting this requires taking values

CAUTION: Using this setting and having child subcommands is not recommended with the exception of also using `crate::Command::args_conflicts_with_subcommands` (or `crate::Command::subcommand_negates_reqs` if the argument marked `Last` is also marked `Arg::required`)

##### Examples

    Arg::new("args")
        .action(ArgAction::Set)
        .last(true)

Setting `last` ensures the arg has the highest index of all positional args and requires that the `--` syntax be used to access it early.

    let res = Command::new("prog")
        .arg(Arg::new("first"))
        .arg(Arg::new("second"))
        .arg(Arg::new("third")
            .action(ArgAction::Set)
            .last(true))
        .try_get_matches_from(vec![
            "prog", "one", "--", "three"
        ]);

    assert!(res.is_ok());
    let m = res.unwrap();
    assert_eq!(m.get_one::<String>("third").unwrap(), "three");
    assert_eq!(m.get_one::<String>("second"), None);

Even if the positional argument marked `Last` is the only argument left to parse, failing to use the `--` syntax results in an error.

    let res = Command::new("prog")
        .arg(Arg::new("first"))
        .arg(Arg::new("second"))
        .arg(Arg::new("third")
            .action(ArgAction::Set)
            .last(true))
        .try_get_matches_from(vec![
            "prog", "one", "two", "three"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::UnknownArgument);

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#### pub fn required(self, yes: bool) -> Self

Specifies that the argument must be present.

Required by default means it is required, when no other conflicting rules or overrides have been evaluated. Conflicting rules take precedence over being required.

Pro tip: Flags (i.e. not positional, or arguments that take values) shouldn’t be required by default. This is because if a flag were to be required, it should simply be implied. No additional information is required from user. Flags by their very nature are simply boolean on/off switches. The only time a user should be required to use a flag is if the operation is destructive in nature, and the user is essentially proving to you, “Yes, I know what I’m doing.”

##### Examples

    Arg::new("config")
        .required(true)

Setting required requires that the argument be used at runtime.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required(true)
            .action(ArgAction::Set)
            .long("config"))
        .try_get_matches_from(vec![
            "prog", "--config", "file.conf",
        ]);

    assert!(res.is_ok());

Setting required and then not supplying that argument at runtime is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required(true)
            .action(ArgAction::Set)
            .long("config"))
        .try_get_matches_from(vec![
            "prog"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

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#### pub fn requires(self, arg_id: impl IntoResettable<Id>) -> Self

Sets an argument that is required when this one is present

i.e. when using this argument, the following argument must be present.

NOTE: Conflicting rules and override rules take precedence over being required

##### Examples

    Arg::new("config")
        .requires("input")

Setting `Arg::requires(name)` requires that the argument be used at runtime if the defining argument is used. If the defining argument isn’t used, the other argument isn’t required

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires("input")
            .long("config"))
        .arg(Arg::new("input"))
        .try_get_matches_from(vec![
            "prog"
        ]);

    assert!(res.is_ok()); // We didn't use cfg, so input wasn't required

Setting `Arg::requires(name)` and not supplying that argument is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires("input")
            .long("config"))
        .arg(Arg::new("input"))
        .try_get_matches_from(vec![
            "prog", "--config", "file.conf"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

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#### pub fn exclusive(self, yes: bool) -> Self

This argument must be passed alone; it conflicts with all other arguments.

##### Examples

    Arg::new("config")
        .exclusive(true)

Setting an exclusive argument and having any other arguments present at runtime is an error.

    let res = Command::new("prog")
        .arg(Arg::new("exclusive")
            .action(ArgAction::Set)
            .exclusive(true)
            .long("exclusive"))
        .arg(Arg::new("debug")
            .long("debug"))
        .arg(Arg::new("input"))
        .try_get_matches_from(vec![
            "prog", "--exclusive", "file.conf", "file.txt"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::ArgumentConflict);

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#### pub fn global(self, yes: bool) -> Self

Specifies that an argument can be matched to all child `Subcommand`s.

NOTE: Global arguments only propagate down, not up (to parent commands), however their values once a user uses them will be propagated back up to parents. In effect, this means one should define all global arguments at the top level, however it doesn’t matter where the user uses the global argument.

##### Examples

Assume an application with two subcommands, and you’d like to define a `--verbose` flag that can be called on any of the subcommands and parent, but you don’t want to clutter the source with three duplicate `Arg` definitions.

    let m = Command::new("prog")
        .arg(Arg::new("verb")
            .long("verbose")
            .short('v')
            .action(ArgAction::SetTrue)
            .global(true))
        .subcommand(Command::new("test"))
        .subcommand(Command::new("do-stuff"))
        .get_matches_from(vec![
            "prog", "do-stuff", "--verbose"
        ]);

    assert_eq!(m.subcommand_name(), Some("do-stuff"));
    let sub_m = m.subcommand_matches("do-stuff").unwrap();
    assert_eq!(*sub_m.get_one::<bool>("verb").expect("defaulted by clap"), true);

source

### impl Arg

#### Value Handling

source

#### pub fn action(self, action: impl IntoResettable<ArgAction>) -> Self

Specify how to react to an argument when parsing it.

ArgAction controls things like

- Overwriting previous values with new ones
- Appending new values to all previous ones
- Counting how many times a flag occurs

The default action is `ArgAction::Set`

##### Examples

    let cmd = Command::new("mycmd")
        .arg(
            Arg::new("flag")
                .long("flag")
                .action(clap::ArgAction::Append)
        );

    let matches = cmd.try_get_matches_from(["mycmd", "--flag", "value"]).unwrap();
    assert!(matches.contains_id("flag"));
    assert_eq!(
        matches.get_many::<String>("flag").unwrap_or_default().map(|v| v.as_str()).collect::<Vec<_>>(),
        vec!["value"]
    );

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#### pub fn value_parser(self, parser: impl IntoResettable<ValueParser>) -> Self

Specify the typed behavior of the argument.

This allows parsing and validating a value before storing it into `ArgMatches` as the given type.

Possible value parsers include:

- `value_parser!(T)` for auto-selecting a value parser for a given type
  - Or range expressions like `0..=1` as a shorthand for `RangedI64ValueParser`
- `Fn(&str) -> Result<T, E>`
- `[&str]` and `PossibleValuesParser` for static enumerated values
- `BoolishValueParser`, and `FalseyValueParser` for alternative `bool` implementations
- `NonEmptyStringValueParser` for basic validation for strings
- or any other `TypedValueParser` implementation

The default value is `ValueParser::string`.

    let mut cmd = clap::Command::new("raw")
        .arg(
            clap::Arg::new("color")
                .long("color")
                .value_parser(["always", "auto", "never"])
                .default_value("auto")
        )
        .arg(
            clap::Arg::new("hostname")
                .long("hostname")
                .value_parser(clap::builder::NonEmptyStringValueParser::new())
                .action(ArgAction::Set)
                .required(true)
        )
        .arg(
            clap::Arg::new("port")
                .long("port")
                .value_parser(clap::value_parser!(u16).range(3000..))
                .action(ArgAction::Set)
                .required(true)
        );

    let m = cmd.try_get_matches_from_mut(
        ["cmd", "--hostname", "rust-lang.org", "--port", "3001"]
    ).unwrap();

    let color: &String = m.get_one("color")
        .expect("default");
    assert_eq!(color, "auto");

    let hostname: &String = m.get_one("hostname")
        .expect("required");
    assert_eq!(hostname, "rust-lang.org");

    let port: u16 = *m.get_one("port")
        .expect("required");
    assert_eq!(port, 3001);

source

#### pub fn num_args(self, qty: impl IntoResettable<ValueRange>) -> Self

Specifies the number of arguments parsed per occurrence

For example, if you had a `-f <file>` argument where you wanted exactly 3 ‘files’ you would set `.num_args(3)`, and this argument wouldn’t be satisfied unless the user provided 3 and only 3 values.

Users may specify values for arguments in any of the following methods

- Using a space such as `-o value` or `--option value`
- Using an equals and no space such as `-o=value` or `--option=value`
- Use a short and no space such as `-ovalue`

WARNING:

Setting a variable number of values (e.g. `1..=10`) for an argument without other details can be dangerous in some circumstances. Because multiple values are allowed, `--option val1 val2 val3` is perfectly valid. Be careful when designing a CLI where positional arguments or subcommands are also expected as `clap` will continue parsing values until one of the following happens:

- It reaches the maximum number of values
- It reaches a specific number of values
- It finds another flag or option (i.e. something that starts with a `-`)
- It reaches the `Arg::value_terminator` if set

Alternatively,

- Use a delimiter between values with Arg::value_delimiter
- Require a flag occurrence per value with `ArgAction::Append`
- Require positional arguments to appear after `--` with `Arg::last`

##### Examples

Option:

    let m = Command::new("prog")
        .arg(Arg::new("mode")
            .long("mode")
            .num_args(1))
        .get_matches_from(vec![
            "prog", "--mode", "fast"
        ]);

    assert_eq!(m.get_one::<String>("mode").unwrap(), "fast");

Flag/option hybrid (see also default_missing_value)

    let cmd = Command::new("prog")
        .arg(Arg::new("mode")
            .long("mode")
            .default_missing_value("slow")
            .default_value("plaid")
            .num_args(0..=1));

    let m = cmd.clone()
        .get_matches_from(vec![
            "prog", "--mode", "fast"
        ]);
    assert_eq!(m.get_one::<String>("mode").unwrap(), "fast");

    let m = cmd.clone()
        .get_matches_from(vec![
            "prog", "--mode",
        ]);
    assert_eq!(m.get_one::<String>("mode").unwrap(), "slow");

    let m = cmd.clone()
        .get_matches_from(vec![
            "prog",
        ]);
    assert_eq!(m.get_one::<String>("mode").unwrap(), "plaid");

Tuples

    let cmd = Command::new("prog")
        .arg(Arg::new("file")
            .action(ArgAction::Set)
            .num_args(2)
            .short('F'));

    let m = cmd.clone()
        .get_matches_from(vec![
            "prog", "-F", "in-file", "out-file"
        ]);
    assert_eq!(
        m.get_many::<String>("file").unwrap_or_default().map(|v| v.as_str()).collect::<Vec<_>>(),
        vec!["in-file", "out-file"]
    );

    let res = cmd.clone()
        .try_get_matches_from(vec![
            "prog", "-F", "file1"
        ]);
    assert_eq!(res.unwrap_err().kind(), ErrorKind::WrongNumberOfValues);

A common mistake is to define an option which allows multiple values and a positional argument.

    let cmd = Command::new("prog")
        .arg(Arg::new("file")
            .action(ArgAction::Set)
            .num_args(0..)
            .short('F'))
        .arg(Arg::new("word"));

    let m = cmd.clone().get_matches_from(vec![
        "prog", "-F", "file1", "file2", "file3", "word"
    ]);
    let files: Vec<_> = m.get_many::<String>("file").unwrap().collect();
    assert_eq!(files, ["file1", "file2", "file3", "word"]); // wait...what?!
    assert!(!m.contains_id("word")); // but we clearly used word!

    // but this works
    let m = cmd.clone().get_matches_from(vec![
        "prog", "word", "-F", "file1", "file2", "file3",
    ]);
    let files: Vec<_> = m.get_many::<String>("file").unwrap().collect();
    assert_eq!(files, ["file1", "file2", "file3"]);
    assert_eq!(m.get_one::<String>("word").unwrap(), "word");

The problem is `clap` doesn’t know when to stop parsing values for “file”.

A solution for the example above is to limit how many values with a maximum, or specific number, or to say `ArgAction::Append` is ok, but multiple values are not.

    let m = Command::new("prog")
        .arg(Arg::new("file")
            .action(ArgAction::Append)
            .short('F'))
        .arg(Arg::new("word"))
        .get_matches_from(vec![
            "prog", "-F", "file1", "-F", "file2", "-F", "file3", "word"
        ]);

    let files: Vec<_> = m.get_many::<String>("file").unwrap().collect();
    assert_eq!(files, ["file1", "file2", "file3"]);
    assert_eq!(m.get_one::<String>("word").unwrap(), "word");

source

#### pub fn value_name(self, name: impl IntoResettable<Str>) -> Self

Placeholder for the argument’s value in the help message / usage.

This name is cosmetic only; the name is not used to access arguments. This setting can be very helpful when describing the type of input the user should be using, such as `FILE`, `INTERFACE`, etc. Although not required, it’s somewhat convention to use all capital letters for the value name.

NOTE: implicitly sets `Arg::action(ArgAction::Set)`

##### Examples

    Arg::new("cfg")
        .long("config")
        .value_name("FILE")

    let m = Command::new("prog")
       .arg(Arg::new("config")
           .long("config")
           .value_name("FILE")
           .help("Some help text"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

Running the above program produces the following output

    valnames

    Usage: valnames [OPTIONS]

    Options:
        --config <FILE>     Some help text
        -h, --help          Print help information
        -V, --version       Print version information

source

#### pub fn value_names(self, names: impl IntoIterator<Item = impl Into<Str>>) -> Self

Placeholders for the argument’s values in the help message / usage.

These names are cosmetic only, used for help and usage strings only. The names are not used to access arguments. The values of the arguments are accessed in numeric order (i.e. if you specify two names `one` and `two` `one` will be the first matched value, `two` will be the second).

This setting can be very helpful when describing the type of input the user should be using, such as `FILE`, `INTERFACE`, etc. Although not required, it’s somewhat convention to use all capital letters for the value name.

Pro Tip: It may help to use `Arg::next_line_help(true)` if there are long, or multiple value names in order to not throw off the help text alignment of all options.

NOTE: implicitly sets `Arg::action(ArgAction::Set)` and `Arg::num_args(1..)`.

##### Examples

    Arg::new("speed")
        .short('s')
        .value_names(["fast", "slow"]);

    let m = Command::new("prog")
       .arg(Arg::new("io")
           .long("io-files")
           .value_names(["INFILE", "OUTFILE"]))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

Running the above program produces the following output

    valnames

    Usage: valnames [OPTIONS]

    Options:
        -h, --help                       Print help information
        --io-files <INFILE> <OUTFILE>    Some help text
        -V, --version                    Print version information

source

#### pub fn value_hint(self, value_hint: impl IntoResettable<ValueHint>) -> Self

Provide the shell a hint about how to complete this argument.

See `ValueHint` for more information.

NOTE: implicitly sets [`Arg::action(ArgAction::Set)`].

For example, to take a username as argument:

    Arg::new("user")
        .short('u')
        .long("user")
        .value_hint(ValueHint::Username);

To take a full command line and its arguments (for example, when writing a command wrapper):

    Command::new("prog")
        .trailing_var_arg(true)
        .arg(
            Arg::new("command")
                .action(ArgAction::Set)
                .num_args(1..)
                .value_hint(ValueHint::CommandWithArguments)
        );

source

#### pub fn ignore_case(self, yes: bool) -> Self

Match values against `PossibleValuesParser` without matching case.

When other arguments are conditionally required based on the value of a case-insensitive argument, the equality check done by `Arg::required_if_eq`, `Arg::required_if_eq_any`, or `Arg::required_if_eq_all` is case-insensitive.

NOTE: Setting this requires taking values

NOTE: To do unicode case folding, enable the `unicode` feature flag.

##### Examples

    let m = Command::new("pv")
        .arg(Arg::new("option")
            .long("option")
            .action(ArgAction::Set)
            .ignore_case(true)
            .value_parser(["test123"]))
        .get_matches_from(vec![
            "pv", "--option", "TeSt123",
        ]);

    assert!(m.get_one::<String>("option").unwrap().eq_ignore_ascii_case("test123"));

This setting also works when multiple values can be defined:

    let m = Command::new("pv")
        .arg(Arg::new("option")
            .short('o')
            .long("option")
            .action(ArgAction::Set)
            .ignore_case(true)
            .num_args(1..)
            .value_parser(["test123", "test321"]))
        .get_matches_from(vec![
            "pv", "--option", "TeSt123", "teST123", "tESt321"
        ]);

    let matched_vals = m.get_many::<String>("option").unwrap().collect::<Vec<_>>();
    assert_eq!(&*matched_vals, &["TeSt123", "teST123", "tESt321"]);

source

#### pub fn allow_hyphen_values(self, yes: bool) -> Self

Allows values which start with a leading hyphen (`-`)

To limit values to just numbers, see `allow_negative_numbers`.

See also `trailing_var_arg`.

NOTE: Setting this requires taking values

WARNING: Prior arguments with `allow_hyphen_values(true)` get precedence over known flags but known flags get precedence over the next possible positional argument with `allow_hyphen_values(true)`. When combined with [`Arg::num_args(..)`], `Arg::value_terminator` is one way to ensure processing stops.

WARNING: Take caution when using this setting combined with another argument using `Arg::num_args`, as this becomes ambiguous `$ prog --arg -- -- val`. All three `--, --, val` will be values when the user may have thought the second `--` would constitute the normal, “Only positional args follow” idiom.

##### Examples

    let m = Command::new("prog")
        .arg(Arg::new("pat")
            .action(ArgAction::Set)
            .allow_hyphen_values(true)
            .long("pattern"))
        .get_matches_from(vec![
            "prog", "--pattern", "-file"
        ]);

    assert_eq!(m.get_one::<String>("pat").unwrap(), "-file");

Not setting `Arg::allow_hyphen_values(true)` and supplying a value which starts with a hyphen is an error.

    let res = Command::new("prog")
        .arg(Arg::new("pat")
            .action(ArgAction::Set)
            .long("pattern"))
        .try_get_matches_from(vec![
            "prog", "--pattern", "-file"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::UnknownArgument);

source

#### pub fn allow_negative_numbers(self, yes: bool) -> Self

Allows negative numbers to pass as values.

This is similar to `Arg::allow_hyphen_values` except that it only allows numbers, all other undefined leading hyphens will fail to parse.

NOTE: Setting this requires taking values

##### Examples

    let res = Command::new("myprog")
        .arg(Arg::new("num").allow_negative_numbers(true))
        .try_get_matches_from(vec![
            "myprog", "-20"
        ]);
    assert!(res.is_ok());
    let m = res.unwrap();
    assert_eq!(m.get_one::<String>("num").unwrap(), "-20");

source

#### pub fn require_equals(self, yes: bool) -> Self

Requires that options use the `--option=val` syntax

i.e. an equals between the option and associated value.

NOTE: Setting this requires taking values

##### Examples

Setting `require_equals` requires that the option have an equals sign between it and the associated value.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .require_equals(true)
            .long("config"))
        .try_get_matches_from(vec![
            "prog", "--config=file.conf"
        ]);

    assert!(res.is_ok());

Setting `require_equals` and not supplying the equals will cause an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .require_equals(true)
            .long("config"))
        .try_get_matches_from(vec![
            "prog", "--config", "file.conf"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::NoEquals);

source

#### pub fn value_delimiter(self, d: impl IntoResettable<char>) -> Self

Allow grouping of multiple values via a delimiter.

i.e. should `--option=val1,val2,val3` be parsed as three values (`val1`, `val2`, and `val3`) or as a single value (`val1,val2,val3`). Defaults to using `,` (comma) as the value delimiter for all arguments that accept values (options and positional arguments)

NOTE: implicitly sets `Arg::action(ArgAction::Set)`

##### Examples

    let m = Command::new("prog")
        .arg(Arg::new("config")
            .short('c')
            .long("config")
            .value_delimiter(','))
        .get_matches_from(vec![
            "prog", "--config=val1,val2,val3"
        ]);

    assert_eq!(m.get_many::<String>("config").unwrap().collect::<Vec<_>>(), ["val1", "val2", "val3"])

source

#### pub fn value_terminator(self, term: impl IntoResettable<Str>) -> Self

Sentinel to stop parsing multiple values of a given argument.

By default when one sets `num_args(1..)` on an argument, clap will continue parsing values for that argument until it reaches another valid argument, or one of the other more specific settings for multiple values is used (such as `num_args`).

NOTE: This setting only applies to options and positional arguments

NOTE: When the terminator is passed in on the command line, it is not stored as one of the values

##### Examples

    Arg::new("vals")
        .action(ArgAction::Set)
        .num_args(1..)
        .value_terminator(";")

The following example uses two arguments, a sequence of commands, and the location in which to perform them

    let m = Command::new("prog")
        .arg(Arg::new("cmds")
            .action(ArgAction::Set)
            .num_args(1..)
            .allow_hyphen_values(true)
            .value_terminator(";"))
        .arg(Arg::new("location"))
        .get_matches_from(vec![
            "prog", "find", "-type", "f", "-name", "special", ";", "/home/clap"
        ]);
    let cmds: Vec<_> = m.get_many::<String>("cmds").unwrap().collect();
    assert_eq!(&cmds, &["find", "-type", "f", "-name", "special"]);
    assert_eq!(m.get_one::<String>("location").unwrap(), "/home/clap");

source

#### pub fn raw(self, yes: bool) -> Self

Consume all following arguments.

Do not be parse them individually, but rather pass them in entirety.

It is worth noting that setting this requires all values to come after a `--` to indicate they should all be captured. For example:

    --foo something -- -v -v -v -b -b -b --baz -q -u -x

Will result in everything after `--` to be considered one raw argument. This behavior may not be exactly what you are expecting and using `crate::Command::trailing_var_arg` may be more appropriate.

NOTE: Implicitly sets `Arg::action(ArgAction::Set)` `Arg::num_args(1..)`, `Arg::allow_hyphen_values(true)`, and `Arg::last(true)` when set to `true`.

source

#### pub fn default_value(self, val: impl IntoResettable<OsStr>) -> Self

Value for the argument when not present.

NOTE: If the user does not use this argument at runtime `ArgMatches::contains_id` will still return `true`. If you wish to determine whether the argument was used at runtime or not, consider `ArgMatches::value_source`.

NOTE: This setting is perfectly compatible with `Arg::default_value_if` but slightly different. `Arg::default_value` only takes effect when the user has not provided this arg at runtime. `Arg::default_value_if` however only takes effect when the user has not provided a value at runtime and these other conditions are met as well. If you have set `Arg::default_value` and `Arg::default_value_if`, and the user did not provide this arg at runtime, nor were the conditions met for `Arg::default_value_if`, the `Arg::default_value` will be applied.

NOTE: This implicitly sets `Arg::action(ArgAction::Set)`.

##### Examples

First we use the default value without providing any value at runtime.

    let m = Command::new("prog")
        .arg(Arg::new("opt")
            .long("myopt")
            .default_value("myval"))
        .get_matches_from(vec![
            "prog"
        ]);

    assert_eq!(m.get_one::<String>("opt").unwrap(), "myval");
    assert!(m.contains_id("opt"));
    assert_eq!(m.value_source("opt"), Some(ValueSource::DefaultValue));

Next we provide a value at runtime to override the default.

    let m = Command::new("prog")
        .arg(Arg::new("opt")
            .long("myopt")
            .default_value("myval"))
        .get_matches_from(vec![
            "prog", "--myopt=non_default"
        ]);

    assert_eq!(m.get_one::<String>("opt").unwrap(), "non_default");
    assert!(m.contains_id("opt"));
    assert_eq!(m.value_source("opt"), Some(ValueSource::CommandLine));

source

#### pub fn default_values(
self,
vals: impl IntoIterator<Item = impl Into<OsStr>>
) -> Self

Value for the argument when not present.

See `Arg::default_value`.

source

#### pub fn default_missing_value(self, val: impl IntoResettable<OsStr>) -> Self

Value for the argument when the flag is present but no value is specified.

This configuration option is often used to give the user a shortcut and allow them to efficiently specify an option argument without requiring an explicitly value. The `--color` argument is a common example. By, supplying an default, such as `default_missing_value("always")`, the user can quickly just add `--color` to the command line to produce the desired color output.

NOTE: using this configuration option requires the use of the `.num_args(0..N)` and the `.require_equals(true)` configuration option. These are required in order to unambiguously determine what, if any, value was supplied for the argument.

##### Examples

For POSIX style `--color`:

    fn cli() -> Command {
        Command::new("prog")
            .arg(Arg::new("color").long("color")
                .value_name("WHEN")
                .value_parser(["always", "auto", "never"])
                .default_value("auto")
                .num_args(0..=1)
                .require_equals(true)
                .default_missing_value("always")
                .help("Specify WHEN to colorize output.")
            )
    }

    // first, we'll provide no arguments
    let m  = cli().get_matches_from(vec![
            "prog"
        ]);
    assert_eq!(m.get_one::<String>("color").unwrap(), "auto");
    assert_eq!(m.value_source("color"), Some(ValueSource::DefaultValue));

    // next, we'll provide a runtime value to override the default (as usually done).
    let m  = cli().get_matches_from(vec![
            "prog", "--color=never"
        ]);
    assert_eq!(m.get_one::<String>("color").unwrap(), "never");
    assert_eq!(m.value_source("color"), Some(ValueSource::CommandLine));

    // finally, we will use the shortcut and only provide the argument without a value.
    let m  = cli().get_matches_from(vec![
            "prog", "--color"
        ]);
    assert_eq!(m.get_one::<String>("color").unwrap(), "always");
    assert_eq!(m.value_source("color"), Some(ValueSource::CommandLine));

For bool literals:

    fn cli() -> Command {
        Command::new("prog")
            .arg(Arg::new("create").long("create")
                .value_name("BOOL")
                .value_parser(value_parser!(bool))
                .num_args(0..=1)
                .require_equals(true)
                .default_missing_value("true")
            )
    }

    // first, we'll provide no arguments
    let m  = cli().get_matches_from(vec![
            "prog"
        ]);
    assert_eq!(m.get_one::<bool>("create").copied(), None);

    // next, we'll provide a runtime value to override the default (as usually done).
    let m  = cli().get_matches_from(vec![
            "prog", "--create=false"
        ]);
    assert_eq!(m.get_one::<bool>("create").copied(), Some(false));
    assert_eq!(m.value_source("create"), Some(ValueSource::CommandLine));

    // finally, we will use the shortcut and only provide the argument without a value.
    let m  = cli().get_matches_from(vec![
            "prog", "--create"
        ]);
    assert_eq!(m.get_one::<bool>("create").copied(), Some(true));
    assert_eq!(m.value_source("create"), Some(ValueSource::CommandLine));

source

#### pub fn default_missing_value_os(self, val: impl Into<OsStr>) -> Self

Value for the argument when the flag is present but no value is specified.

See `Arg::default_missing_value`.

source

#### pub fn default_missing_values(
self,
vals: impl IntoIterator<Item = impl Into<OsStr>>
) -> Self

Value for the argument when the flag is present but no value is specified.

See `Arg::default_missing_value`.

source

#### pub fn default_missing_values_os(
self,
vals: impl IntoIterator<Item = impl Into<OsStr>>
) -> Self

Value for the argument when the flag is present but no value is specified.

See `Arg::default_missing_values`.

source

### impl Arg

#### Help

source

#### pub fn help(self, h: impl IntoResettable<StyledStr>) -> Self

Sets the description of the argument for short help (`-h`).

Typically, this is a short (one line) description of the arg.

If `Arg::long_help` is not specified, this message will be displayed for `--help`.

NOTE: Only `Arg::help` is used in completion script generation in order to be concise

##### Examples

Any valid UTF-8 is allowed in the help text. The one exception is when one wishes to include a newline in the help text and have the following text be properly aligned with all the other help text.

Setting `help` displays a short message to the side of the argument when the user passes `-h` or `--help` (by default).

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays

    helptest

    Usage: helptest [OPTIONS]

    Options:
        --config     Some help text describing the --config arg
    -h, --help       Print help information
    -V, --version    Print version information

source

#### pub fn long_help(self, h: impl IntoResettable<StyledStr>) -> Self

Sets the description of the argument for long help (`--help`).

Typically this a more detailed (multi-line) message that describes the arg.

If `Arg::help` is not specified, this message will be displayed for `-h`.

NOTE: Only `Arg::help` is used in completion script generation in order to be concise

##### Examples

Any valid UTF-8 is allowed in the help text. The one exception is when one wishes to include a newline in the help text and have the following text be properly aligned with all the other help text.

Setting `help` displays a short message to the side of the argument when the user passes `-h` or `--help` (by default).

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .long_help(
    "The config file used by the myprog must be in JSON format
    with only valid keys and may not contain other nonsense
    that cannot be read by this program. Obviously I'm going on
    and on, so I'll stop now."))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays

    prog

    Usage: prog [OPTIONS]

    Options:
            --config
                The config file used by the myprog must be in JSON format
                with only valid keys and may not contain other nonsense
                that cannot be read by this program. Obviously I'm going on
                and on, so I'll stop now.

        -h, --help
                Print help information

        -V, --version
                Print version information

source

#### pub fn display_order(self, ord: impl IntoResettable<usize>) -> Self

Allows custom ordering of args within the help message.

Args with a lower value will be displayed first in the help message. This is helpful when one would like to emphasise frequently used args, or prioritize those towards the top of the list. Args with duplicate display orders will be displayed in alphabetical order.

NOTE: The default is 999 for all arguments.

NOTE: This setting is ignored for positional arguments which are always displayed in index order.

##### Examples

    let m = Command::new("prog")
       .arg(Arg::new("a") // Typically args are grouped alphabetically by name.
                                // Args without a display_order have a value of 999 and are
                                // displayed alphabetically with all other 999 valued args.
           .long("long-option")
           .short('o')
           .action(ArgAction::Set)
           .help("Some help and text"))
       .arg(Arg::new("b")
           .long("other-option")
           .short('O')
           .action(ArgAction::Set)
           .display_order(1)   // In order to force this arg to appear *first*
                               // all we have to do is give it a value lower than 999.
                               // Any other args with a value of 1 will be displayed
                               // alphabetically with this one...then 2 values, then 3, etc.
           .help("I should be first!"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays the following help message

    cust-ord

    Usage: cust-ord [OPTIONS]

    Options:
        -h, --help                Print help information
        -V, --version             Print version information
        -O, --other-option <b>    I should be first!
        -o, --long-option <a>     Some help and text

source

#### pub fn help_heading(self, heading: impl IntoResettable<Str>) -> Self

Override the current help section.

source

#### pub fn next_line_help(self, yes: bool) -> Self

Render the help on the line after the argument.

This can be helpful for arguments with very long or complex help messages. This can also be helpful for arguments with very long flag names, or many/long value names.

NOTE: To apply this setting to all arguments and subcommands, consider using `crate::Command::next_line_help`

##### Examples

    let m = Command::new("prog")
       .arg(Arg::new("opt")
           .long("long-option-flag")
           .short('o')
           .action(ArgAction::Set)
           .next_line_help(true)
           .value_names(["value1", "value2"])
           .help("Some really long help and complex\n\
                  help that makes more sense to be\n\
                  on a line after the option"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays the following help message

    nlh

    Usage: nlh [OPTIONS]

    Options:
        -h, --help       Print help information
        -V, --version    Print version information
        -o, --long-option-flag <value1> <value2>
            Some really long help and complex
            help that makes more sense to be
            on a line after the option

source

#### pub fn hide(self, yes: bool) -> Self

Do not display the argument in help message.

NOTE: This does not hide the argument from usage strings on error

##### Examples

Setting `Hidden` will hide the argument when displaying help text

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .hide(true)
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays

    helptest

    Usage: helptest [OPTIONS]

    Options:
    -h, --help       Print help information
    -V, --version    Print version information

source

#### pub fn hide_possible_values(self, yes: bool) -> Self

Do not display the possible values in the help message.

This is useful for args with many values, or ones which are explained elsewhere in the help text.

NOTE: Setting this requires taking values

To set this for all arguments, see `Command::hide_possible_values`.

##### Examples

    let m = Command::new("prog")
        .arg(Arg::new("mode")
            .long("mode")
            .value_parser(["fast", "slow"])
            .action(ArgAction::Set)
            .hide_possible_values(true));

If we were to run the above program with `--help` the `[values: fast, slow]` portion of the help text would be omitted.

source

#### pub fn hide_default_value(self, yes: bool) -> Self

Do not display the default value of the argument in the help message.

This is useful when default behavior of an arg is explained elsewhere in the help text.

NOTE: Setting this requires taking values

##### Examples

    let m = Command::new("connect")
        .arg(Arg::new("host")
            .long("host")
            .default_value("localhost")
            .action(ArgAction::Set)
            .hide_default_value(true));

If we were to run the above program with `--help` the `[default: localhost]` portion of the help text would be omitted.

source

#### pub fn hide_short_help(self, yes: bool) -> Self

Hides an argument from short help (`-h`).

NOTE: This does not hide the argument from usage strings on error

NOTE: Setting this option will cause next-line-help output style to be used when long help (`--help`) is called.

##### Examples

    Arg::new("debug")
        .hide_short_help(true);

Setting `hide_short_help(true)` will hide the argument when displaying short help text

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .hide_short_help(true)
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "-h"
       ]);

The above example displays

    helptest

    Usage: helptest [OPTIONS]

    Options:
    -h, --help       Print help information
    -V, --version    Print version information

However, when –help is called

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .hide_short_help(true)
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

Then the following would be displayed

    helptest

    Usage: helptest [OPTIONS]

    Options:
        --config     Some help text describing the --config arg
    -h, --help       Print help information
    -V, --version    Print version information

source

#### pub fn hide_long_help(self, yes: bool) -> Self

Hides an argument from long help (`--help`).

NOTE: This does not hide the argument from usage strings on error

NOTE: Setting this option will cause next-line-help output style to be used when long help (`--help`) is called.

##### Examples

Setting `hide_long_help(true)` will hide the argument when displaying long help text

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .hide_long_help(true)
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "--help"
       ]);

The above example displays

    helptest

    Usage: helptest [OPTIONS]

    Options:
    -h, --help       Print help information
    -V, --version    Print version information

However, when -h is called

    let m = Command::new("prog")
       .arg(Arg::new("cfg")
           .long("config")
           .hide_long_help(true)
           .help("Some help text describing the --config arg"))
       .get_matches_from(vec![
           "prog", "-h"
       ]);

Then the following would be displayed

    helptest

    Usage: helptest [OPTIONS]

    OPTIONS:
        --config     Some help text describing the --config arg
    -h, --help       Print help information
    -V, --version    Print version information

source

### impl Arg

#### Advanced Argument Relations

source

#### pub fn group(self, group_id: impl IntoResettable<Id>) -> Self

The name of the `ArgGroup` the argument belongs to.

##### Examples

    Arg::new("debug")
        .long("debug")
        .action(ArgAction::SetTrue)
        .group("mode")

Multiple arguments can be a member of a single group and then the group checked as if it was one of said arguments.

    let m = Command::new("prog")
        .arg(Arg::new("debug")
            .long("debug")
            .action(ArgAction::SetTrue)
            .group("mode"))
        .arg(Arg::new("verbose")
            .long("verbose")
            .action(ArgAction::SetTrue)
            .group("mode"))
        .get_matches_from(vec![
            "prog", "--debug"
        ]);
    assert!(m.contains_id("mode"));

source

#### pub fn groups(self, group_ids: impl IntoIterator<Item = impl Into<Id>>) -> Self

The names of `ArgGroup`’s the argument belongs to.

##### Examples

    Arg::new("debug")
        .long("debug")
        .action(ArgAction::SetTrue)
        .groups(["mode", "verbosity"])

Arguments can be members of multiple groups and then the group checked as if it was one of said arguments.

    let m = Command::new("prog")
        .arg(Arg::new("debug")
            .long("debug")
            .action(ArgAction::SetTrue)
            .groups(["mode", "verbosity"]))
        .arg(Arg::new("verbose")
            .long("verbose")
            .action(ArgAction::SetTrue)
            .groups(["mode", "verbosity"]))
        .get_matches_from(vec![
            "prog", "--debug"
        ]);
    assert!(m.contains_id("mode"));
    assert!(m.contains_id("verbosity"));

source

#### pub fn default_value_if(
self,
arg_id: impl Into<Id>,
predicate: impl Into<ArgPredicate>,
default: impl IntoResettable<OsStr>
) -> Self

Specifies the value of the argument if `arg` has been used at runtime.

If `default` is set to `None`, `default_value` will be removed.

NOTE: This setting is perfectly compatible with `Arg::default_value` but slightly different. `Arg::default_value` only takes effect when the user has not provided this arg at runtime. This setting however only takes effect when the user has not provided a value at runtime and these other conditions are met as well. If you have set `Arg::default_value` and `Arg::default_value_if`, and the user did not provide this arg at runtime, nor were the conditions met for `Arg::default_value_if`, the `Arg::default_value` will be applied.

NOTE: This implicitly sets `Arg::action(ArgAction::Set)`.

##### Examples

First we use the default value only if another arg is present at runtime.

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("other")
            .long("other")
            .default_value_if("flag", ArgPredicate::IsPresent, Some("default")))
        .get_matches_from(vec![
            "prog", "--flag"
        ]);

    assert_eq!(m.get_one::<String>("other").unwrap(), "default");

Next we run the same test, but without providing `--flag`.

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("other")
            .long("other")
            .default_value_if("flag", "true", Some("default")))
        .get_matches_from(vec![
            "prog"
        ]);

    assert_eq!(m.get_one::<String>("other"), None);

Now lets only use the default value if `--opt` contains the value `special`.

    let m = Command::new("prog")
        .arg(Arg::new("opt")
            .action(ArgAction::Set)
            .long("opt"))
        .arg(Arg::new("other")
            .long("other")
            .default_value_if("opt", "special", Some("default")))
        .get_matches_from(vec![
            "prog", "--opt", "special"
        ]);

    assert_eq!(m.get_one::<String>("other").unwrap(), "default");

We can run the same test and provide any value other than `special` and we won’t get a default value.

    let m = Command::new("prog")
        .arg(Arg::new("opt")
            .action(ArgAction::Set)
            .long("opt"))
        .arg(Arg::new("other")
            .long("other")
            .default_value_if("opt", "special", Some("default")))
        .get_matches_from(vec![
            "prog", "--opt", "hahaha"
        ]);

    assert_eq!(m.get_one::<String>("other"), None);

If we want to unset the default value for an Arg based on the presence or value of some other Arg.

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("other")
            .long("other")
            .default_value("default")
            .default_value_if("flag", "true", None))
        .get_matches_from(vec![
            "prog", "--flag"
        ]);

    assert_eq!(m.get_one::<String>("other"), None);

source

#### pub fn default_value_ifs(
self,
ifs: impl IntoIterator<Item = (impl Into<Id>, impl Into<ArgPredicate>, impl IntoResettable<OsStr>)>
) -> Self

Specifies multiple values and conditions in the same manner as `Arg::default_value_if`.

The method takes a slice of tuples in the `(arg, predicate, default)` format.

NOTE: The conditions are stored in order and evaluated in the same order. I.e. the first if multiple conditions are true, the first one found will be applied and the ultimate value.

##### Examples

First we use the default value only if another arg is present at runtime.

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("opt")
            .long("opt")
            .action(ArgAction::Set))
        .arg(Arg::new("other")
            .long("other")
            .default_value_ifs([
                ("flag", "true", Some("default")),
                ("opt", "channal", Some("chan")),
            ]))
        .get_matches_from(vec![
            "prog", "--opt", "channal"
        ]);

    assert_eq!(m.get_one::<String>("other").unwrap(), "chan");

Next we run the same test, but without providing `--flag`.

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("other")
            .long("other")
            .default_value_ifs([
                ("flag", "true", Some("default")),
                ("opt", "channal", Some("chan")),
            ]))
        .get_matches_from(vec![
            "prog"
        ]);

    assert_eq!(m.get_one::<String>("other"), None);

We can also see that these values are applied in order, and if more than one condition is true, only the first evaluated “wins”

    let m = Command::new("prog")
        .arg(Arg::new("flag")
            .long("flag")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("opt")
            .long("opt")
            .action(ArgAction::Set))
        .arg(Arg::new("other")
            .long("other")
            .default_value_ifs([
                ("flag", ArgPredicate::IsPresent, Some("default")),
                ("opt", ArgPredicate::Equals("channal".into()), Some("chan")),
            ]))
        .get_matches_from(vec![
            "prog", "--opt", "channal", "--flag"
        ]);

    assert_eq!(m.get_one::<String>("other").unwrap(), "default");

source

#### pub fn required_unless_present(self, arg_id: impl IntoResettable<Id>) -> Self

Set this arg as required as long as the specified argument is not present at runtime.

Pro Tip: Using `Arg::required_unless_present` implies `Arg::required` and is therefore not mandatory to also set.

##### Examples

    Arg::new("config")
        .required_unless_present("debug")

In the following example, the required argument is not provided, but it’s not an error because the `unless` arg has been supplied.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present("dbg")
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug")
            .action(ArgAction::SetTrue))
        .try_get_matches_from(vec![
            "prog", "--debug"
        ]);

    assert!(res.is_ok());

Setting `Arg::required_unless_present(name)` and not supplying `name` or this arg is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present("dbg")
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug"))
        .try_get_matches_from(vec![
            "prog"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn required_unless_present_all(
self,
names: impl IntoIterator<Item = impl Into<Id>>
) -> Self

Sets this arg as required unless all of the specified arguments are present at runtime.

In other words, parsing will succeed only if user either

- supplies the `self` arg.
- supplies all of the `names` arguments.

NOTE: If you wish for this argument to only be required unless any of these args are present see `Arg::required_unless_present_any`

##### Examples

    Arg::new("config")
        .required_unless_present_all(["cfg", "dbg"])

In the following example, the required argument is not provided, but it’s not an error because all of the `names` args have been supplied.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present_all(["dbg", "infile"])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("infile")
            .short('i')
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--debug", "-i", "file"
        ]);

    assert!(res.is_ok());

Setting `Arg::required_unless_present_all(names)` and not supplying either all of `unless` args or the `self` arg is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present_all(["dbg", "infile"])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("infile")
            .short('i')
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn required_unless_present_any(
self,
names: impl IntoIterator<Item = impl Into<Id>>
) -> Self

Sets this arg as required unless any of the specified arguments are present at runtime.

In other words, parsing will succeed only if user either

- supplies the `self` arg.
- supplies one or more of the `unless` arguments.

NOTE: If you wish for this argument to be required unless all of these args are present see `Arg::required_unless_present_all`

##### Examples

    Arg::new("config")
        .required_unless_present_any(["cfg", "dbg"])

Setting `Arg::required_unless_present_any(names)` requires that the argument be used at runtime unless at least one of the args in `names` are present. In the following example, the required argument is not provided, but it’s not an error because one the `unless` args have been supplied.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present_any(["dbg", "infile"])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("infile")
            .short('i')
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--debug"
        ]);

    assert!(res.is_ok());

Setting `Arg::required_unless_present_any(names)` and not supplying at least one of `names` or this arg is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_unless_present_any(["dbg", "infile"])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("dbg")
            .long("debug")
            .action(ArgAction::SetTrue))
        .arg(Arg::new("infile")
            .short('i')
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn required_if_eq(self, arg_id: impl Into<Id>, val: impl Into<OsStr>) -> Self

This argument is required only if the specified `arg` is present at runtime and its value equals `val`.

##### Examples

    Arg::new("config")
        .required_if_eq("other_arg", "value")

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .required_if_eq("other", "special")
            .long("config"))
        .arg(Arg::new("other")
            .long("other")
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--other", "not-special"
        ]);

    assert!(res.is_ok()); // We didn't use --other=special, so "cfg" wasn't required

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .required_if_eq("other", "special")
            .long("config"))
        .arg(Arg::new("other")
            .long("other")
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--other", "special"
        ]);

    // We did use --other=special so "cfg" had become required but was missing.
    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .required_if_eq("other", "special")
            .long("config"))
        .arg(Arg::new("other")
            .long("other")
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--other", "SPECIAL"
        ]);

    // By default, the comparison is case-sensitive, so "cfg" wasn't required
    assert!(res.is_ok());

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .required_if_eq("other", "special")
            .long("config"))
        .arg(Arg::new("other")
            .long("other")
            .ignore_case(true)
            .action(ArgAction::Set))
        .try_get_matches_from(vec![
            "prog", "--other", "SPECIAL"
        ]);

    // However, case-insensitive comparisons can be enabled.  This typically occurs when using Arg::possible_values().
    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn required_if_eq_any(
self,
ifs: impl IntoIterator<Item = (impl Into<Id>, impl Into<OsStr>)>
) -> Self

Specify this argument is required based on multiple conditions.

The conditions are set up in a `(arg, val)` style tuple. The requirement will only become valid if one of the specified `arg`’s value equals its corresponding `val`.

##### Examples

    Arg::new("config")
        .required_if_eq_any([
            ("extra", "val"),
            ("option", "spec")
        ])

Setting `Arg::required_if_eq_any([(arg, val)])` makes this arg required if any of the `arg`s are used at runtime and it’s corresponding value is equal to `val`. If the `arg`’s value is anything other than `val`, this argument isn’t required.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_if_eq_any([
                ("extra", "val"),
                ("option", "spec")
            ])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("extra")
            .action(ArgAction::Set)
            .long("extra"))
        .arg(Arg::new("option")
            .action(ArgAction::Set)
            .long("option"))
        .try_get_matches_from(vec![
            "prog", "--option", "other"
        ]);

    assert!(res.is_ok()); // We didn't use --option=spec, or --extra=val so "cfg" isn't required

Setting `Arg::required_if_eq_any([(arg, val)])` and having any of the `arg`s used with its value of `val` but not using this arg is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_if_eq_any([
                ("extra", "val"),
                ("option", "spec")
            ])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("extra")
            .action(ArgAction::Set)
            .long("extra"))
        .arg(Arg::new("option")
            .action(ArgAction::Set)
            .long("option"))
        .try_get_matches_from(vec![
            "prog", "--option", "spec"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn required_if_eq_all(
self,
ifs: impl IntoIterator<Item = (impl Into<Id>, impl Into<OsStr>)>
) -> Self

Specify this argument is required based on multiple conditions.

The conditions are set up in a `(arg, val)` style tuple. The requirement will only become valid if every one of the specified `arg`’s value equals its corresponding `val`.

##### Examples

    Arg::new("config")
        .required_if_eq_all([
            ("extra", "val"),
            ("option", "spec")
        ])

Setting `Arg::required_if_eq_all([(arg, val)])` makes this arg required if all of the `arg`s are used at runtime and every value is equal to its corresponding `val`. If the `arg`’s value is anything other than `val`, this argument isn’t required.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_if_eq_all([
                ("extra", "val"),
                ("option", "spec")
            ])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("extra")
            .action(ArgAction::Set)
            .long("extra"))
        .arg(Arg::new("option")
            .action(ArgAction::Set)
            .long("option"))
        .try_get_matches_from(vec![
            "prog", "--option", "spec"
        ]);

    assert!(res.is_ok()); // We didn't use --option=spec --extra=val so "cfg" isn't required

Setting `Arg::required_if_eq_all([(arg, val)])` and having all of the `arg`s used with its value of `val` but not using this arg is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .required_if_eq_all([
                ("extra", "val"),
                ("option", "spec")
            ])
            .action(ArgAction::Set)
            .long("config"))
        .arg(Arg::new("extra")
            .action(ArgAction::Set)
            .long("extra"))
        .arg(Arg::new("option")
            .action(ArgAction::Set)
            .long("option"))
        .try_get_matches_from(vec![
            "prog", "--extra", "val", "--option", "spec"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn requires_if(
self,
val: impl Into<ArgPredicate>,
arg_id: impl Into<Id>
) -> Self

Require another argument if this arg matches the `ArgPredicate`

This method takes `value, another_arg` pair. At runtime, clap will check if this arg (`self`) matches the `ArgPredicate`. If it does, `another_arg` will be marked as required.

##### Examples

    Arg::new("config")
        .requires_if("val", "arg")

Setting `Arg::requires_if(val, arg)` requires that the `arg` be used at runtime if the defining argument’s value is equal to `val`. If the defining argument is anything other than `val`, the other argument isn’t required.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires_if("my.cfg", "other")
            .long("config"))
        .arg(Arg::new("other"))
        .try_get_matches_from(vec![
            "prog", "--config", "some.cfg"
        ]);

    assert!(res.is_ok()); // We didn't use --config=my.cfg, so other wasn't required

Setting `Arg::requires_if(val, arg)` and setting the value to `val` but not supplying `arg` is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires_if("my.cfg", "input")
            .long("config"))
        .arg(Arg::new("input"))
        .try_get_matches_from(vec![
            "prog", "--config", "my.cfg"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn requires_ifs(
self,
ifs: impl IntoIterator<Item = (impl Into<ArgPredicate>, impl Into<Id>)>
) -> Self

Allows multiple conditional requirements.

The requirement will only become valid if this arg’s value matches the `ArgPredicate`.

##### Examples

    Arg::new("config")
        .requires_ifs([
            ("val", "arg"),
            ("other_val", "arg2"),
        ])

Setting `Arg::requires_ifs(["val", "arg"])` requires that the `arg` be used at runtime if the defining argument’s value is equal to `val`. If the defining argument’s value is anything other than `val`, `arg` isn’t required.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires_ifs([
                ("special.conf", "opt"),
                ("other.conf", "other"),
            ])
            .long("config"))
        .arg(Arg::new("opt")
            .long("option")
            .action(ArgAction::Set))
        .arg(Arg::new("other"))
        .try_get_matches_from(vec![
            "prog", "--config", "special.conf"
        ]);

    assert!(res.is_err()); // We  used --config=special.conf so --option <val> is required
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

Setting `Arg::requires_ifs` with `ArgPredicate::IsPresent` and not supplying all the arguments is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .requires_ifs([
                (ArgPredicate::IsPresent, "input"),
                (ArgPredicate::IsPresent, "output"),
            ])
            .long("config"))
        .arg(Arg::new("input"))
        .arg(Arg::new("output"))
        .try_get_matches_from(vec![
            "prog", "--config", "file.conf", "in.txt"
        ]);

    assert!(res.is_err());
    // We didn't use output
    assert_eq!(res.unwrap_err().kind(), ErrorKind::MissingRequiredArgument);

source

#### pub fn conflicts_with(self, arg_id: impl IntoResettable<Id>) -> Self

This argument is mutually exclusive with the specified argument.

NOTE: Conflicting rules take precedence over being required by default. Conflict rules only need to be set for one of the two arguments, they do not need to be set for each.

NOTE: Defining a conflict is two-way, but does not need to defined for both arguments (i.e. if A conflicts with B, defining A.conflicts_with(B) is sufficient. You do not need to also do B.conflicts_with(A))

NOTE: `Arg::conflicts_with_all(names)` allows specifying an argument which conflicts with more than one argument.

NOTE `Arg::exclusive(true)` allows specifying an argument which conflicts with every other argument.

NOTE: All arguments implicitly conflict with themselves.

##### Examples

    Arg::new("config")
        .conflicts_with("debug")

Setting conflicting argument, and having both arguments present at runtime is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .conflicts_with("debug")
            .long("config"))
        .arg(Arg::new("debug")
            .long("debug")
            .action(ArgAction::SetTrue))
        .try_get_matches_from(vec![
            "prog", "--debug", "--config", "file.conf"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::ArgumentConflict);

source

#### pub fn conflicts_with_all(
self,
names: impl IntoIterator<Item = impl Into<Id>>
) -> Self

This argument is mutually exclusive with the specified arguments.

See `Arg::conflicts_with`.

NOTE: Conflicting rules take precedence over being required by default. Conflict rules only need to be set for one of the two arguments, they do not need to be set for each.

NOTE: Defining a conflict is two-way, but does not need to defined for both arguments (i.e. if A conflicts with B, defining A.conflicts_with(B) is sufficient. You do not need need to also do B.conflicts_with(A))

NOTE: `Arg::exclusive(true)` allows specifying an argument which conflicts with every other argument.

##### Examples

    Arg::new("config")
        .conflicts_with_all(["debug", "input"])

Setting conflicting argument, and having any of the arguments present at runtime with a conflicting argument is an error.

    let res = Command::new("prog")
        .arg(Arg::new("cfg")
            .action(ArgAction::Set)
            .conflicts_with_all(["debug", "input"])
            .long("config"))
        .arg(Arg::new("debug")
            .long("debug"))
        .arg(Arg::new("input"))
        .try_get_matches_from(vec![
            "prog", "--config", "file.conf", "file.txt"
        ]);

    assert!(res.is_err());
    assert_eq!(res.unwrap_err().kind(), ErrorKind::ArgumentConflict);

source

#### pub fn overrides_with(self, arg_id: impl IntoResettable<Id>) -> Self

Sets an overridable argument.

i.e. this argument and the following argument will override each other in POSIX style (whichever argument was specified at runtime last “wins”)

NOTE: When an argument is overridden it is essentially as if it never was used, any conflicts, requirements, etc. are evaluated after all “overrides” have been removed

NOTE: Overriding an argument implies they conflict.

##### Examples

    let m = Command::new("prog")
        .arg(arg!(-f --flag "some flag")
            .conflicts_with("debug"))
        .arg(arg!(-d --debug "other flag"))
        .arg(arg!(-c --color "third flag")
            .overrides_with("flag"))
        .get_matches_from(vec![
            "prog", "-f", "-d", "-c"]);
                //    ^~~~~~~~~~~~^~~~~ flag is overridden by color

    assert!(*m.get_one::<bool>("color").unwrap());
    assert!(*m.get_one::<bool>("debug").unwrap()); // even though flag conflicts with debug, it's as if flag
                                    // was never used because it was overridden with color
    assert!(!*m.get_one::<bool>("flag").unwrap());

source

#### pub fn overrides_with_all(
self,
names: impl IntoIterator<Item = impl Into<Id>>
) -> Self

Sets multiple mutually overridable arguments by name.

i.e. this argument and the following argument will override each other in POSIX style (whichever argument was specified at runtime last “wins”)

NOTE: When an argument is overridden it is essentially as if it never was used, any conflicts, requirements, etc. are evaluated after all “overrides” have been removed

NOTE: Overriding an argument implies they conflict.

##### Examples

    let m = Command::new("prog")
        .arg(arg!(-f --flag "some flag")
            .conflicts_with("color"))
        .arg(arg!(-d --debug "other flag"))
        .arg(arg!(-c --color "third flag")
            .overrides_with_all(["flag", "debug"]))
        .get_matches_from(vec![
            "prog", "-f", "-d", "-c"]);
                //    ^~~~~~^~~~~~~~~ flag and debug are overridden by color

    assert!(*m.get_one::<bool>("color").unwrap()); // even though flag conflicts with color, it's as if flag
                                    // and debug were never used because they were overridden
                                    // with color
    assert!(!*m.get_one::<bool>("debug").unwrap());
    assert!(!*m.get_one::<bool>("flag").unwrap());

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### impl Arg

#### Reflection

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#### pub fn get_id(&self) -> &Id

Get the name of the argument

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#### pub fn get_help(&self) -> Option<&StyledStr>

Get the help specified for this argument, if any

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#### pub fn get_long_help(&self) -> Option<&StyledStr>

Get the long help specified for this argument, if any

##### Examples

    let arg = Arg::new("foo").long_help("long help");
    assert_eq!(Some("long help".to_owned()), arg.get_long_help().map(|s| s.to_string()));

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#### pub fn get_help_heading(&self) -> Option<&str>

Get the help heading specified for this argument, if any

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#### pub fn get_short(&self) -> Option<char>

Get the short option name for this argument, if any

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#### pub fn get_visible_short_aliases(&self) -> Option<Vec<char>>

Get visible short aliases for this argument, if any

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#### pub fn get_all_short_aliases(&self) -> Option<Vec<char>>

Get all short aliases for this argument, if any, both visible and hidden.

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#### pub fn get_short_and_visible_aliases(&self) -> Option<Vec<char>>

Get the short option name and its visible aliases, if any

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#### pub fn get_long(&self) -> Option<&str>

Get the long option name for this argument, if any

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#### pub fn get_visible_aliases(&self) -> Option<Vec<&str>>

Get visible aliases for this argument, if any

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#### pub fn get_all_aliases(&self) -> Option<Vec<&str>>

Get all aliases for this argument, if any, both visible and hidden.

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#### pub fn get_long_and_visible_aliases(&self) -> Option<Vec<&str>>

Get the long option name and its visible aliases, if any

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#### pub fn get_possible_values(&self) -> Vec<PossibleValue>

Get the names of possible values for this argument. Only useful for user facing applications, such as building help messages or man files

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#### pub fn get_value_names(&self) -> Option<&[Str]>

Get the names of values for this argument.

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#### pub fn get_num_args(&self) -> Option<ValueRange>

Get the number of values for this argument.

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#### pub fn get_value_delimiter(&self) -> Option<char>

Get the delimiter between multiple values

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#### pub fn get_index(&self) -> Option<usize>

Get the index of this argument, if any

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#### pub fn get_value_hint(&self) -> ValueHint

Get the value hint of this argument

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#### pub fn get_default_values(&self) -> &[OsStr]

Get the default values specified for this argument, if any

##### Examples

    let arg = Arg::new("foo").default_value("default value");
    assert_eq!(arg.get_default_values(), &["default value"]);

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#### pub fn is_positional(&self) -> bool

Checks whether this argument is a positional or not.

##### Examples

    let arg = Arg::new("foo");
    assert_eq!(arg.is_positional(), true);

    let arg = Arg::new("foo").long("foo");
    assert_eq!(arg.is_positional(), false);

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#### pub fn is_required_set(&self) -> bool

Reports whether `Arg::required` is set

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#### pub fn is_allow_hyphen_values_set(&self) -> bool

Report whether `Arg::allow_hyphen_values` is set

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#### pub fn is_allow_negative_numbers_set(&self) -> bool

Report whether `Arg::allow_negative_numbers` is set

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#### pub fn get_action(&self) -> &ArgAction

Behavior when parsing the argument

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#### pub fn get_value_parser(&self) -> &ValueParser

Configured parser for argument values

##### Example

    let cmd = clap::Command::new("raw")
        .arg(
            clap::Arg::new("port")
                .value_parser(clap::value_parser!(usize))
        );
    let value_parser = cmd.get_arguments()
        .find(|a| a.get_id() == "port").unwrap()
        .get_value_parser();
    println!("{:?}", value_parser);

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#### pub fn is_global_set(&self) -> bool

Report whether `Arg::global` is set

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#### pub fn is_next_line_help_set(&self) -> bool

Report whether `Arg::next_line_help` is set

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#### pub fn is_hide_set(&self) -> bool

Report whether `Arg::hide` is set

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#### pub fn is_hide_default_value_set(&self) -> bool

Report whether `Arg::hide_default_value` is set

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#### pub fn is_hide_possible_values_set(&self) -> bool

Report whether `Arg::hide_possible_values` is set

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#### pub fn is_hide_short_help_set(&self) -> bool

Report whether `Arg::hide_short_help` is set

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#### pub fn is_hide_long_help_set(&self) -> bool

Report whether `Arg::hide_long_help` is set

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#### pub fn is_require_equals_set(&self) -> bool

Report whether `Arg::require_equals` is set

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#### pub fn is_exclusive_set(&self) -> bool

Reports whether `Arg::exclusive` is set

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#### pub fn is_trailing_var_arg_set(&self) -> bool

Report whether `Arg::trailing_var_arg` is set

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#### pub fn is_last_set(&self) -> bool

Reports whether `Arg::last` is set

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#### pub fn is_ignore_case_set(&self) -> bool

Reports whether `Arg::ignore_case` is set

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### impl Arg

This impl block contains no items.

#### Internally used only

## Trait Implementations

source

### impl Clone for Arg

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#### fn clone(&self) -> Arg

Returns a copy of the value. Read more

1.0.0 · source

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more

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### impl Debug for Arg

source

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more

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### impl Default for Arg

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#### fn default() -> Arg

Returns the “default value” for a type. Read more

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### impl Display for Arg

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

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### impl From<&Arg> for Arg

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#### fn from(a: &Arg) -> Self

Converts to this type from the input type.

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### impl Ord for Arg

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#### fn cmp(&self, other: &Arg) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more

1.21.0 · source

#### fn max(self, other: Self) -> Self

Compares and returns the maximum of two values. Read more

1.21.0 · source

#### fn min(self, other: Self) -> Self

Compares and returns the minimum of two values. Read more

1.50.0 · source

#### fn clamp(self, min: Self, max: Self) -> Self where
Self: PartialOrd<Self>,

Restrict a value to a certain interval. Read more

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### impl PartialEq<Arg> for Arg

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#### fn eq(&self, other: &Arg) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

1.0.0 · source

#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`.

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### impl PartialOrd<Arg> for Arg

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#### fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more

1.0.0 · source

#### fn lt(&self, other: &Rhs) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

1.0.0 · source

#### fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

1.0.0 · source

#### fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

1.0.0 · source

#### fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

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### impl Eq for Arg

## Auto Trait Implementations

### impl !RefUnwindSafe for Arg

### impl Send for Arg

### impl Sync for Arg

### impl Unpin for Arg

### impl !UnwindSafe for Arg

## Blanket Implementations

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

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### impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for T where
T: Clone,

#### type Owned = T

The resulting type after obtaining ownership.

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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

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### impl<T> ToString for T where
T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

source

### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.