Enum clap::builder::ArgAction

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#[non_exhaustive]
pub enum ArgAction { Set, Append, SetTrue, SetFalse, Count, Help, Version, }
Expand description

Behavior of arguments when they are encountered while parsing

§Examples

let cmd = Command::new("mycmd")
   .arg(
       Arg::new("special-help")
           .short('?')
           .action(clap::ArgAction::Help)
   );

// Existing help still exists
let err = cmd.clone().try_get_matches_from(["mycmd", "-h"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayHelp);

// New help available
let err = cmd.try_get_matches_from(["mycmd", "-?"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayHelp);

Variants (Non-exhaustive)§

This enum is marked as non-exhaustive
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.
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Set

When encountered, store the associated value(s) in ArgMatches

NOTE: If the argument has previously been seen, it will result in a ArgumentConflict unless Command::args_override_self(true) is set.

§Examples

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

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"]
);
§

Append

When encountered, store the associated value(s) in ArgMatches

§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", "value1", "--flag", "value2"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_many::<String>("flag").unwrap_or_default().map(|v| v.as_str()).collect::<Vec<_>>(),
    vec!["value1", "value2"]
);
§

SetTrue

When encountered, act as if "true" was encountered on the command-line

If no default_value is set, it will be false.

No value is allowed. To optionally accept a value, see Arg::default_missing_value

NOTE: If the argument has previously been seen, it will result in a ArgumentConflict unless Command::args_override_self(true) is set.

§Examples

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

let matches = cmd.clone().try_get_matches_from(["mycmd", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<bool>("flag").copied(),
    Some(true)
);

let matches = cmd.try_get_matches_from(["mycmd"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<bool>("flag").copied(),
    Some(false)
);

You can use TypedValueParser::map to have the flag control an application-specific type:

let cmd = Command::new("mycmd")
    .arg(
        Arg::new("flag")
            .long("flag")
            .action(clap::ArgAction::SetTrue)
            .value_parser(
                BoolishValueParser::new()
                .map(|b| -> usize {
                    if b { 10 } else { 5 }
                })
            )
    );

let matches = cmd.clone().try_get_matches_from(["mycmd", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<usize>("flag").copied(),
    Some(10)
);

let matches = cmd.try_get_matches_from(["mycmd"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<usize>("flag").copied(),
    Some(5)
);
§

SetFalse

When encountered, act as if "false" was encountered on the command-line

If no default_value is set, it will be true.

No value is allowed. To optionally accept a value, see Arg::default_missing_value

NOTE: If the argument has previously been seen, it will result in a ArgumentConflict unless Command::args_override_self(true) is set.

§Examples

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

let matches = cmd.clone().try_get_matches_from(["mycmd", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<bool>("flag").copied(),
    Some(false)
);

let matches = cmd.try_get_matches_from(["mycmd"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_one::<bool>("flag").copied(),
    Some(true)
);
§

Count

When encountered, increment a u8 counter

If no default_value is set, it will be 0.

No value is allowed. To optionally accept a value, see Arg::default_missing_value

§Examples

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

let matches = cmd.clone().try_get_matches_from(["mycmd", "--flag", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_count("flag"),
    2
);

let matches = cmd.try_get_matches_from(["mycmd"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(
    matches.get_count("flag"),
    0
);
§

Help

When encountered, display Command::print_help

Depending on the flag, Command::print_long_help may be shown

§Examples

let cmd = Command::new("mycmd")
   .arg(
       Arg::new("special-help")
           .short('?')
           .action(clap::ArgAction::Help)
   );

// Existing help still exists
let err = cmd.clone().try_get_matches_from(["mycmd", "-h"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayHelp);

// New help available
let err = cmd.try_get_matches_from(["mycmd", "-?"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayHelp);
§

Version

When encountered, display Command::version

Depending on the flag, Command::long_version may be shown

§Examples

let cmd = Command::new("mycmd")
    .version("1.0.0")
    .arg(
        Arg::new("special-version")
            .long("special-version")
            .action(clap::ArgAction::Version)
    );

// Existing help still exists
let err = cmd.clone().try_get_matches_from(["mycmd", "--version"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayVersion);

// New help available
let err = cmd.try_get_matches_from(["mycmd", "--special-version"]).unwrap_err();
assert_eq!(err.kind(), clap::error::ErrorKind::DisplayVersion);

Implementations§

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impl ArgAction

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pub fn takes_values(&self) -> bool

Returns whether this action accepts values on the command-line

default_values and [env][super::Arg::env] may still be processed.

Trait Implementations§

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impl Clone for ArgAction

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fn clone(&self) -> ArgAction

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 ArgAction

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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 IntoResettable<ArgAction> for ArgAction

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fn into_resettable(self) -> Resettable<ArgAction>

Convert to the intended resettable type
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impl IntoResettable<ArgAction> for Option<ArgAction>

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fn into_resettable(self) -> Resettable<ArgAction>

Convert to the intended resettable type

Auto Trait 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,

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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,

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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

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fn from(t: T) -> T

Returns the argument unchanged.

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

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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,

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

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.