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Learn Rust Coding · Lesson

clap Basics

Argument parsing.

Why clap?

clap (Command Line Argument Parser) is the de-facto standard crate for building CLIs in Rust.

  • Parses arguments, flags, and options
  • Generates --help and --version automatically
  • Validates input and reports friendly errors

Without it you would manually iterate over std::env::args() and handle every edge case yourself.

Reading args by hand

Before reaching for clap, it helps to see the raw approach. std::env::args() yields an iterator where the first item is the program name.

fn main() {
    let args: Vec<String> = std::env::args().collect();
    println!("Program: {}", args[0]);
    println!("Got {} extra arg(s)", args.len() - 1);
}

All lessons in this course

  1. clap Basics
  2. Subcommands
  3. Derive API
  4. Validation and Help
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