Struct clap::Arg

pub struct Arg { /* private fields */ }

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 Args, 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

impl Arg

Basic API

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

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")

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

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

See Arg::new for more details.

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

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"));

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

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"));

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

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");

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

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");

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

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_flag("test"), true);

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

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_flag("test"), true);

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

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");

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

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");

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

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_flag("test"), true);

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

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_flag("test"), true);

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

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 (debug builds)

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

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

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"]);

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

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);

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

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);

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

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);

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

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);

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

Specifies that an argument can be matched to all child Subcommands.

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_flag("verb"), true);

impl Arg

Value Handling

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

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"]
);

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

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);

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

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");

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

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

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

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

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

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)
    );

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

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"]);

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

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);

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

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");

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

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);

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

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"])

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

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");

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

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 Arg::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.

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

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.

Like with command-line values, this will be split by Arg::value_delimiter.

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));

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

Value for the argument when not present.

See Arg::default_value.

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

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.

Like with command-line values, this will be split by Arg::value_delimiter.

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));

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

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

See Arg::default_missing_value.

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

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

See Arg::default_missing_value.

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

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

See Arg::default_missing_values.

pub fn env(self, name: impl IntoResettable<OsStr>) -> Arg

Read from name environment variable when argument is not present.

If it is not present in the environment, then default rules will apply.

If user sets the argument in the environment:

• When Arg::action(ArgAction::Set) is not set, the flag is considered raised.
• When Arg::action(ArgAction::Set) is set, ArgMatches::get_one will return value of the environment variable.

If user doesn’t set the argument in the environment:

• When Arg::action(ArgAction::Set) is not set, the flag is considered off.
• When Arg::action(ArgAction::Set) is set, ArgMatches::get_one will return the default specified.

Like with command-line values, this will be split by Arg::value_delimiter.

Examples

In this example, we show the variable coming from the environment:

env::set_var("MY_FLAG", "env");

let m = Command::new("prog")
    .arg(Arg::new("flag")
        .long("flag")
        .env("MY_FLAG")
        .action(ArgAction::Set))
    .get_matches_from(vec![
        "prog"
    ]);

assert_eq!(m.get_one::<String>("flag").unwrap(), "env");

In this example, because prog is a flag that accepts an optional, case-insensitive boolean literal.

Note that the value parser controls how flags are parsed. In this case we’ve selected FalseyValueParser. A false literal is n, no, f, false, off or 0. An absent environment variable will also be considered as false. Anything else will considered as true.

env::set_var("TRUE_FLAG", "true");
env::set_var("FALSE_FLAG", "0");

let m = Command::new("prog")
    .arg(Arg::new("true_flag")
        .long("true_flag")
        .action(ArgAction::SetTrue)
        .value_parser(FalseyValueParser::new())
        .env("TRUE_FLAG"))
    .arg(Arg::new("false_flag")
        .long("false_flag")
        .action(ArgAction::SetTrue)
        .value_parser(FalseyValueParser::new())
        .env("FALSE_FLAG"))
    .arg(Arg::new("absent_flag")
        .long("absent_flag")
        .action(ArgAction::SetTrue)
        .value_parser(FalseyValueParser::new())
        .env("ABSENT_FLAG"))
    .get_matches_from(vec![
        "prog"
    ]);

assert!(m.get_flag("true_flag"));
assert!(!m.get_flag("false_flag"));
assert!(!m.get_flag("absent_flag"));

In this example, we show the variable coming from an option on the CLI:

env::set_var("MY_FLAG", "env");

let m = Command::new("prog")
    .arg(Arg::new("flag")
        .long("flag")
        .env("MY_FLAG")
        .action(ArgAction::Set))
    .get_matches_from(vec![
        "prog", "--flag", "opt"
    ]);

assert_eq!(m.get_one::<String>("flag").unwrap(), "opt");

In this example, we show the variable coming from the environment even with the presence of a default:

env::set_var("MY_FLAG", "env");

let m = Command::new("prog")
    .arg(Arg::new("flag")
        .long("flag")
        .env("MY_FLAG")
        .action(ArgAction::Set)
        .default_value("default"))
    .get_matches_from(vec![
        "prog"
    ]);

assert_eq!(m.get_one::<String>("flag").unwrap(), "env");

In this example, we show the use of multiple values in a single environment variable:

env::set_var("MY_FLAG_MULTI", "env1,env2");

let m = Command::new("prog")
    .arg(Arg::new("flag")
        .long("flag")
        .env("MY_FLAG_MULTI")
        .action(ArgAction::Set)
        .num_args(1..)
        .value_delimiter(','))
    .get_matches_from(vec![
        "prog"
    ]);

assert_eq!(m.get_many::<String>("flag").unwrap().collect::<Vec<_>>(), vec!["env1", "env2"]);

impl Arg

Help

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

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

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

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

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

Allows custom ordering of args within the help message.

Args with a lower value will be displayed first in the help message. Those with the same display order will be sorted.

Args are automatically assigned a display order based on the order they are added to the Command. Overriding this is helpful when the order arguments are added in isn’t the same as the display order, whether in one-off cases or to automatically sort arguments.

To change, see Command::next_display_order.

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

Examples

let m = Command::new("prog")
    .arg(Arg::new("boat")
        .short('b')
        .long("boat")
        .action(ArgAction::Set)
        .display_order(0)  // Sort
        .help("Some help and text"))
    .arg(Arg::new("airplane")
        .short('a')
        .long("airplane")
        .action(ArgAction::Set)
        .display_order(0)  // Sort
        .help("I should be first!"))
    .arg(Arg::new("custom-help")
        .short('?')
        .action(ArgAction::Help)
        .display_order(100)  // Don't sort
        .help("Alt help"))
    .get_matches_from(vec![
        "prog", "--help"
    ]);

The above example displays the following help message

cust-ord

Usage: cust-ord [OPTIONS]

Options:
    -a, --airplane <airplane>    I should be first!
    -b, --boat <boar>            Some help and text
    -h, --help                   Print help information
    -?                           Alt help

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

Override the current help section.

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

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

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

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

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

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.

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

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.

pub fn hide_env(self, yes: bool) -> Arg

Do not display in help the environment variable name.

This is useful when the variable option is explained elsewhere in the help text.

Examples

let m = Command::new("prog")
    .arg(Arg::new("mode")
        .long("mode")
        .env("MODE")
        .action(ArgAction::Set)
        .hide_env(true));

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

pub fn hide_env_values(self, yes: bool) -> Arg

Do not display in help any values inside the associated ENV variables for the argument.

This is useful when ENV vars contain sensitive values.

Examples

let m = Command::new("connect")
    .arg(Arg::new("host")
        .long("host")
        .env("CONNECT")
        .action(ArgAction::Set)
        .hide_env_values(true));

If we were to run the above program with $ CONNECT=super_secret connect --help the [default: CONNECT=super_secret] portion of the help text would be omitted.

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

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

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

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

impl Arg

Advanced Argument Relations

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

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"));

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

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"));

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

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.

Like with command-line values, this will be split by Arg::value_delimiter.

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);

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

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.

Like with command-line values, this will be split by Arg::value_delimiter.

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");

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

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);

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

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);

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

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);

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

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);

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

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 args 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 args 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);

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

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 args 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 args 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);

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

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);

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

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);

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

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);

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

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);

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

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_flag("color"));
assert!(m.get_flag("debug")); // even though flag conflicts with debug, it's as if flag
                                // was never used because it was overridden with color
assert!(!m.get_flag("flag"));

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

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_flag("color")); // 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_flag("debug"));
assert!(!m.get_flag("flag"));

impl Arg

Reflection

pub fn get_id(&self) -> &Id

Get the name of the argument

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

Get the help specified for this argument, if any

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()));

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

Get the help heading specified for this argument, if any

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

Get the short option name for this argument, if any

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

Get visible short aliases for this argument, if any

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

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

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

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

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

Get the long option name for this argument, if any

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

Get visible aliases for this argument, if any

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

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

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

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

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

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

Get the names of values for this argument.

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

Get the number of values for this argument.

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

Get the delimiter between multiple values

pub fn get_value_terminator(&self) -> Option<&Str>

Get the value terminator for this argument. The value_terminator is a value that terminates parsing of multi-valued arguments.

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

Get the index of this argument, if any

pub fn get_value_hint(&self) -> ValueHint

Get the value hint of this argument

pub fn get_env(&self) -> Option<&OsStr>

Get the environment variable name specified for this argument, if any

Examples

let arg = Arg::new("foo").env("ENVIRONMENT");
assert_eq!(arg.get_env(), Some(OsStr::new("ENVIRONMENT")));

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"]);

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);

pub fn is_required_set(&self) -> bool

Reports whether Arg::required is set

pub fn is_allow_hyphen_values_set(&self) -> bool

Report whether Arg::allow_hyphen_values is set

pub fn is_allow_negative_numbers_set(&self) -> bool

Report whether Arg::allow_negative_numbers is set

pub fn get_action(&self) -> &ArgAction

Behavior when parsing the argument

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:?}");

pub fn is_global_set(&self) -> bool

Report whether Arg::global is set

pub fn is_next_line_help_set(&self) -> bool

Report whether Arg::next_line_help is set

pub fn is_hide_set(&self) -> bool

Report whether Arg::hide is set

pub fn is_hide_default_value_set(&self) -> bool

Report whether Arg::hide_default_value is set

pub fn is_hide_possible_values_set(&self) -> bool

Report whether Arg::hide_possible_values is set

pub fn is_hide_env_set(&self) -> bool

Report whether Arg::hide_env is set

pub fn is_hide_env_values_set(&self) -> bool

Report whether Arg::hide_env_values is set

pub fn is_hide_short_help_set(&self) -> bool

Report whether Arg::hide_short_help is set

pub fn is_hide_long_help_set(&self) -> bool

Report whether Arg::hide_long_help is set

pub fn is_require_equals_set(&self) -> bool

Report whether Arg::require_equals is set

pub fn is_exclusive_set(&self) -> bool

Reports whether Arg::exclusive is set

pub fn is_trailing_var_arg_set(&self) -> bool

Report whether Arg::trailing_var_arg is set

pub fn is_last_set(&self) -> bool

Reports whether Arg::last is set

pub fn is_ignore_case_set(&self) -> bool

Reports whether Arg::ignore_case is set

impl Arg

This impl block contains no items.

Internally used only

Trait Implementations

impl Clone for Arg

fn clone(&self) -> Arg

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Arg

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

Formats the value using the given formatter.

impl Default for Arg

fn default() -> Arg

Returns the “default value” for a type.

impl Display for Arg

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

Formats the value using the given formatter.

impl From<&Arg> for Arg

fn from(a: &Arg) -> Arg

Converts to this type from the input type.

impl Ord for Arg

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

This method returns an Ordering between self and other.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl PartialEq for Arg

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

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

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for Arg

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

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

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

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

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

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

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

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

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

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

impl Eq for Arg