Variants

Set

When encountered, store the associated value(s) in [ArgMatches][crate::ArgMatches]

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

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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][crate::ArgMatches]

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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][super::Arg::default_value] is set, it will be false.

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

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

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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_flag("flag"),
    true
);

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

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

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
# use clap::builder::TypedValueParser as _;
# use clap::builder::BoolishValueParser;
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][super::Arg::default_value] is set, it will be true.

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

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

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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_flag("flag"),
    false
);

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

Count

When encountered, increment a u8 counter starting from 0.

If no [default_value][super::Arg::default_value] is set, it will be 0.

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

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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][super::Command::print_help]

Depending on the flag, [Command::print_long_help][super::Command::print_long_help] may be shown

Examples

# #[cfg(feature = "help")] {
# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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);
# }

HelpShort

When encountered, display [Command::print_help][super::Command::print_help]

Examples

# #[cfg(feature = "help")] {
# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
let cmd = Command::new("mycmd")
    .arg(
        Arg::new("special-help")
            .short('?')
            .action(clap::ArgAction::HelpShort)
    );

// 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);
# }

HelpLong

When encountered, display [Command::print_long_help][super::Command::print_long_help]

Examples

# #[cfg(feature = "help")] {
# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
let cmd = Command::new("mycmd")
    .arg(
        Arg::new("special-help")
            .short('?')
            .action(clap::ArgAction::HelpLong)
    );

// 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][super::Command::version]

Depending on the flag, [Command::long_version][super::Command::long_version] may be shown

Examples

# use clap_builder as clap;
# use clap::Command;
# use clap::Arg;
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);