# Enum clap::ArgAction

source · [−]

    #[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.

### `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

source

### impl ArgAction

source

#### 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

source

### impl Debug for ArgAction

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

Formats the value using the given formatter. Read more

source

### 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

### impl RefUnwindSafe for ArgAction

### impl Send for ArgAction

### impl Sync for ArgAction

### impl Unpin for ArgAction

### impl UnwindSafe for ArgAction

## Blanket Implementations

source

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

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

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

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

const: unstable · source

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

Immutably borrows from an owned value. Read more

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

const: unstable · source

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

Mutably borrows from an owned value. Read more

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

const: unstable · source

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

Returns the argument unchanged.

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

const: unstable · source

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

Calls `U::from(self)`.

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

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

#### type Owned = T

The resulting type after obtaining ownership.

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

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

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

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

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

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

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

Performs the conversion.

source

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

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

The type returned in the event of a conversion error.

const: unstable · source

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

Performs the conversion.