Enum clap::builder::ArgAction

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

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)

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

impl ArgAction

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

impl Clone for ArgAction

fn clone(&self) -> ArgAction

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for ArgAction

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

Formats the value using the given formatter.

impl IntoResettable<ArgAction> for ArgAction

fn into_resettable(self) -> Resettable<ArgAction>

Convert to the intended resettable type

impl IntoResettable<ArgAction> for Option<ArgAction>

fn into_resettable(self) -> Resettable<ArgAction>

Convert to the intended resettable type