Stdin

Some console programs can benefit from being interactive—when the user types a string, they print a message. This can be done with the stdin function in Rust.

By calling read_line in a loop, we can keep accessing the data typed by the user. But to get the line we have to clear the buffer of data.

An example

To begin, we need to include the std io module—this includes the stdin() function that we need to call. We create a buffer string.

Info In Rust, Strings have growable buffers, so they can be used as a buffering type. They optimize out allocations.

Here We call read_line on stdin in a while loop. Read_line returns a Result, so we call is_ok() to ensure we get something.

Tip To ensure the line data is as easy to process as possible, we can call trim_end to remove trailing newlines (and spaces).

use std::io;

fn main() {
    // Read in input.
    let mut buffer = String::new();
    let stdin = io::stdin();
    while stdin.read_line(&mut buffer).is_ok() {
        // Trim end.
        let trimmed = buffer.trim_end();
        println!("You typed: [{trimmed}]");
        buffer.clear();
    }
}test
You typed: [test]
hello
You typed: [hello]
friend
You typed: [friend]

Discussion

In my experience, having a command-line program that does one thing and exits is the easiest approach. This allows it to be called from other programs more easily.

However For some types of programs an interactive command line parser can be a better experience. Try stdin and find out.

A summary

We read lines from the command line in an interactive Rust program, and trimmed the end of the strings. A program could run certain functions based on typed input.