Number as a simultaneous flag and value

[mbhall88]

Please complete the following tasks

• I have searched the discussions
• I have searched the existing issues

Clap Version

2.33

Describe your use case

I would like to have a special option that I can designate that the flag passed on the command line is the actual value also.

Describe the solution you'd like

The feature I am asking for is effectively how the compression level flag in gzip works. i.e., gzip -9 indicates the best compression, gzip -1 the fastest, and gzip -5 is in-between.

The way I could envision this working would be to have a special symbol # to indicate this, something like

let m = App::new("gzip")
    .arg(Arg::with_name("#"))
    .get_matches_from(vec![
        "gzip", "-3"
    ]);
assert!(m.is_present("#"));
assert_eq!(m.value_of("#"), Some(3));

Alternatives, if applicable

No response

Additional Context

No response

[pksunkara]

Hey, this is definitely possible on 3.0.0-beta.4 and should be possible on 2.33 too. Not sure what gave you the impression that it is not. Please read the documentation and try it out and open a bug report if it's not working.

[mbhall88]

I did read the documentation, but obviously I missed the relevant option for doing this. Are you able to point me in the right direction?

[pksunkara]

What's the value you are getting for m.is_present("#") and m.value_of("#")?

[mbhall88]

When I try and build this I get

error: Found argument '-3' which wasn't expected, or isn't valid in this context

USAGE:
    gzip [#]

For more information try --help

[pksunkara]

Use https://docs.rs/clap/2.33.3/clap/struct.Arg.html#method.allow_hyphen_values for that arg.

[mbhall88]

I'm still getting the same error.

use clap::{Arg, App};

fn main() {
    let m = App::new("gzip")
        .arg(Arg::with_name("#").allow_hyphen_values(true))
        .get_matches_from(vec!["gzip", "-3"]);
    assert!(m.is_present("#"));
    assert_eq!(m.value_of("#"), Some("3"));
}

$ cargo run

[pksunkara]

This works on v3

[mbhall88]

Ok, I'll wait until v3 is stable and revisit this then

[kbknapp]

On v2 it seems to be a bug with using Arg::hyphen_values on free/positional arguments. This bug requires you to also use AppSettings::AllowLeadingHyphen:

fn main() {
    let m = App::new("gzip")
        .setting(AppSettings::AllowLeadingHyphen)
        .arg(Arg::with_name("#").allow_hyphen_values(true))
        .get_matches_from(vec!["gzip", "-3"]);
    assert!(m.is_present("#"));
    assert_eq!(m.value_of("#"), Some("-3"));
}

Note the value includes the - character which you'll have to strip for your pruposes.