How to use clap to take create a vector

Question

I have a basic struct like this

pub struct Args {
  #[clap(short, long, value_parser)]
  pub files: Vec<String>,
}

I'm trying to get this struct to take multiple values like such

cargo run -- --files hello world

But when I run this, it doesn't see world correctly. It errors with this:

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

What is the proper way to have clap populate this struct?

Answer 1

You can use num_args to specify a range for the number of argument occurences and values allowed like so:

use clap::Parser;

#[derive(Parser)]
pub struct Args {
    #[clap(short, long, value_parser, num_args = 1.., value_delimiter = ' ')]
    pub files: Vec<String>,
  }

fn main() {
    let args = Args::parse();

    println!("files: {:?}", args.files);
}

This will allow both

cargo run -- --files hello world

and

cargo run -- --files hello --files world

Specifying the value_delimiter is not strictly neccessary here, but I just wanted to point out that you can use different characters as delimiters like this.

If you also want to allow empty arrays beeing passed, you can change the num_args attribute like so num_args = 0...