Rust - lesson 4 | HackIndia Skills

Rust - lesson 4 | HackIndia Skills | HackIndia

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();

    let command = args.get(1);

    match command {
        Some(cmd) if cmd == "add" => println!("Add a new item"),
        Some(cmd) if cmd == "list" => println!("Show all items"),
        Some(cmd) if cmd == "done" => println!("Mark an item done"),
        Some(other) => println!("Unknown command: {}", other),
        None => println!("Usage: tasker add|list|done"),
    }
}

Tip

Prefer exact shapes

When possible, match on simple values. For command strings, you can convert Option into Option so your arms look cleaner.

This reduces guard clauses like if cmd == "add".

use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();
    let command = args.get(1).map(String::as_str);

    match command {
        Some("add") => println!("Add a new item"),
        Some("list") => println!("Show all items"),
        Some("done") => println!("Mark an item done"),
        Some(other) => println!("Unknown command: {}", other),
        None => println!("Usage: tasker add|list|done"),
    }
}

Example

Match parsed input

A CLI often receives text and needs a number. You can match the parse result and choose what to do.

This keeps error handling close to the input that caused it.

fn handle_done(input: &str) {
    match input.parse::<usize>() {
        Ok(id) => println!("Mark task {} as done", id),
        Err(_) => println!("Please give a number, like: tasker done 2"),
    }
}

fn main() {
    handle_done("2");
    handle_done("two");
}

Your to-do

Do this now

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Open your Rust CLI project or create a small practice file.
Add a command match for at least three commands and one unknown command.
Add a None branch that prints a usage line.
Parse one argument as a number and match Ok and Err.
Run cargo run with valid, missing, and wrong inputs.

0 of 5 done

cargo run -- add
cargo run -- list
cargo run -- done 2
cargo run -- done two
cargo run

Match data into actions

One idea

Why it matters

Match a command

Read the match

Prefer exact shapes

Do not skip cases

Match parsed input

Do this now

Quick check