#[non_exhaustive]
pub enum ArgAction {
    Set,
    Append,
    StoreValue,
    IncOccurrence,
    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

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.occurrences_of("flag"), 0);
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.occurrences_of("flag"), 0);
assert_eq!(
    matches.get_many::<String>("flag").unwrap_or_default().map(|v| v.as_str()).collect::<Vec<_>>(),
    vec!["value1", "value2"]
);

StoreValue

Deprecated, replaced with ArgAction::Set or ArgAction::Append

Builder: Instead of arg.action(ArgAction::StoreValue),

  • Use arg.action(ArgAction::Set) for single-occurrence arguments
  • Use arg.action(ArgAction::Append) for multiple-occurrence arguments

Derive: opt-in to the new behavior with #[clap(action)]

IncOccurrence

Deprecated, replaced with ArgAction::SetTrue or ArgAction::Count

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

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", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(matches.occurrences_of("flag"), 0);
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.occurrences_of("flag"), 0);
assert_eq!(
    matches.get_one::<bool>("flag").copied(),
    Some(false)
);

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

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", "--flag"]).unwrap();
assert!(matches.contains_id("flag"));
assert_eq!(matches.occurrences_of("flag"), 0);
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.occurrences_of("flag"), 0);
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.occurrences_of("flag"), 0);
assert_eq!(
    matches.get_count("flag"),
    2
);

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

Returns whether this action accepts values on the command-line

default_values and env may still be processed.

Trait Implementations

Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.