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devexamples

Command Line Arguments With clap

Define a CLI interface with clap derives so arguments are parsed, validated, and documented from one struct declaration.

RustCli Tooling

Code

snippet
use clap::Parser;
use std::path::PathBuf;

#[derive(Parser, Debug)]
#[command(name = "convert", about = "Convert files between formats")]
struct Cli {
    input: PathBuf,

    #[arg(short, long, default_value_t = 1)]
    level: u8,

    #[arg(short, long)]
    output: Option<PathBuf>,

    #[arg(long, default_value_t = false)]
    verbose: bool,
}

fn main() {
    let cli = Cli::parse();
    if cli.level == 0 || cli.level > 9 {
        eprintln!("level must be between 1 and 9");
        std::process::exit(2);
    }
    let output = cli.output.unwrap_or_else(|| cli.input.with_extension("out"));
    if cli.verbose {
        println!("input={:?} output={:?} level={}", cli.input, output, cli.level);
    }
}

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