70 %

Building a Rust CLI with subcommands using structopt and clap

I have a pre-existing CLI that uses subcommands. In this case it's named toast and the subcommand I care about is toast incremental. Using structopt we can derive our arguments from an enum to generate subcommands:

rust

use std::path::PathBuf;
use structopt::StructOpt;

#[derive(Debug, StructOpt)]
#[structopt(name = "toast", about = "The best place to stack your JAM")]
enum Toast {
    Incremental {
        /// Activate debug mode
        // short and long flags (-d, --debug) will be deduced from the field's name
        #[structopt(short, long)]
        debug: bool,

        /// Input file
        #[structopt(parse(from_os_str))]
        input_dir: PathBuf,

        /// Output file, stdout if not present
        #[structopt(parse(from_os_str))]
        output_dir: Option<PathBuf>,
    },
}

fn main() {
    let opt = Toast::from_args();
    println!("{:?}", opt);
}

This will yield us a command that can be run as such:

shell

toast incremental

error: The following required arguments were not provided:
    <input-dir>

USAGE:
    toast incremental [FLAGS] <input-dir> [output-dir]

For more information try --help

Note that the input is required, so we have to run it with the input directory in this case.

➜ ./target/debug/toast incremental ./test-toast-site
Incremental { debug: false, input_dir: "./test-toast-site", output_dir: None }

The result is a struct that we can do whatever we want with from here.

rust

Incremental {
  debug: false,
  input_dir: "./test-toast-site",
  output_dir: None
}