Env args

A Rust program can accept command-line arguments. Suppose we want to pass a simple argument to a program like a folder name.

With env args, a method in std, we can loop over the arguments to a program. The first argument is the name of the program itself.

Example program

In this simple example, we try to detect a "folder" argument to the program. Then, the next string in the arguments is the folder name itself.

use std::env;

fn main() {
    let mut folder_next = false;
    let mut folder = String::new();
    // Part 1: loop over arguments.
    for argument in env::args() {
        // ... Display arguments.
        println!("Argument: {}", argument);

        // Part 2: use flag after "-folder" was detected to set argument.
        if folder_next {
            folder = argument;
            folder_next = false;
            continue;
        }

        // Part 3: if "-folder" detected, set flag bool.
        if argument == "-folder" {
            folder_next = true;
            continue;
        }
    }

    // Result.
    println!("Folder argument: {}", folder)
}
.hello-rust -folder ~/temp/&
Argument: ./hello-rust
Argument: -folder
Argument: /Users/sam/temp/
Folder argument: /Users/sam/temp/

String new, notes

If we use the empty string literal (which is a str reference) as the folder local, we will get a compiler error. This is the "mismatched types" error in Rust.

Summary

We developed a simple command-line flag argument parser in Rust. This code could be adapted to consider more arguments, and even provide parsing of types.