Example of Rust CLI program that uses the clap crate

clap_example.rs

use anyhow::Result;
use clap::Parser;
use std::{
    io::Write,
    path::{Path, PathBuf},
};

#[derive(Parser)]
#[command(version, about, long_about = None)]
struct Cli {
    /// Path to the input configuration file
    #[arg(short, long, required = true)]
    input: PathBuf,

    /// Path for the output timetable file
    #[arg(short, long, required = true)]
    output: PathBuf,
}

fn main() -> Result<()> {
    let Cli { input, output } = Cli::parse();

    if !validate_args(&input, &output)? {
        return Ok(());
    }

    Ok(())
}

fn confirm_overwrite() -> Result<bool> {
    eprint!("Warning: output file already exists.\nOverwrite it? [y/N]: ");
    std::io::stderr().flush()?;

    let mut input = String::new();
    std::io::stdin().read_line(&mut input)?;

    let response = input.trim().to_lowercase();
    Ok(matches!(response.as_str(), "y" | "yes"))
}

fn validate_args(input: &Path, output: &Path) -> Result<bool> {
    if !input.try_exists()? {
        anyhow::bail!("Input file does not exist: {}", input.display());
    }

    if !input.is_file() {
        anyhow::bail!("Input path is not a file: {}", input.display());
    }

    if output.try_exists()? && !confirm_overwrite()? {
        eprintln!("Exiting...");
        return Ok(false);
    }

    //TODO: Check validity of input file format

    Ok(true)
}