Getting command line arguments in Rust is a fundamental technique that every Rust developer should know. Command-line arguments are specified after the name of a program in command-line operating systems like UNIX or Linux and are passed in to the program from the environment. The Rust Standard Library makes it easy to read command-line arguments.
One of the most useful aspects of command line arguments is that they allow us to alter the behavior of our program, without changing the program itself. This opens up a world of possibilities, from simply changing the output, to loading different configuration files, and even toggling debugging information.
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Getting Command Line Arguments
Take a look at the following code snippet:
use std::env;
fn main() {
let args: Vec
println!(“{:?}”, args);
}
This simple program gathers all the command line arguments as a Vec
We start off by importing the std::env module, which provides functions for interacting with the environment of the running program. Secondly, we define a function main where we’ll handle our arguments. Subsequently, inside the main function we collect the arguments into a Vector of strings. Lastly, we print each argument passed on the command line to the console.
Interpreting the Code
In the above Rust program, we first import the `env` module from the Rust Standard Library with `use std::env;`. This module provides us with a function `args()` that returns an iterator that allows us to access each argument passed to the program.
It’s important to understand that this iterator returns a series of `OsString`. OsString is a Rust structure that stores a string in a form suitable for interfacing with the operating system. However, it’s not very friendly to work with directly, so we convert them to `String`s by using the `collect()` function which gathers all the elements of the iterator into a collection—in this case, a `Vec`.
Understanding Libraries and Functions Involved
The std::env module is part of the Rust Standard Library. It provides a variety of functionalities to interact with the operating system. In this case, we used the `args()` function to access the arguments passed from command line.
The `collect()` function is a very powerful function in Rust related to iterators. An iterator is something that allows iterating over a sequence of data. With `collect()` we can transform an iterator into a collection like Vec or HashMap. Here, we used it to transform our command line arguments into a collection of Strings.
Going Beyond Basic Command Line Arguments
While simply printing out the command line arguments is useful for basic programs, larger applications often require more sophisticated handling of command line input. This includes things like parsing options, flags, and subcommands, handling errors, providing help messages, and more. For such tasks, you would turn to libraries like `docopt` or `clap`, which provide comprehensive solutions for parsing command line arguments and handling complex CLI interfaces.
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