Getting values from Deno stdin

Question

How can we get values from standard input in Deno?

I don't know how to use Deno.stdin.

An example would be appreciated.

Answer 1

We can use prompt in deno.

const input = prompt('Please enter input');

In case input has to be a number. We can use Number.parseInt(input);

Answer 2

Deno.stdin is of type File, thus you can read from it by providing a Uint8Array as buffer and call Deno.stdin.read(buf)

window.onload = async function main() {
  const buf = new Uint8Array(1024);
  /* Reading into `buf` from start.
   * buf.subarray(0, n) is the read result.
   * If n is instead Deno.EOF, then it means that stdin is closed.
   */
  const n = await Deno.stdin.read(buf); 
  if (n == Deno.EOF) {
    console.log("Standard input closed")
  } else {
    console.log("READ:", new TextDecoder().decode(buf.subarray(0, n)));
  }
}

Answer 3

A simple confirmation which can be answered with y or n:

import { readLines } from "https://deno.land/std/io/buffer.ts";

async function confirm(question) {
    console.log(question);

    for await (const line of readLines(Deno.stdin)) {
        if (line === "y") {
            return true;
        } else if (line === "n") {
            return false;
        }
    }
}

const answer = await confirm("Do you want to go on? [y/n]");

Or if you want to prompt the user for a string:

import { readLines } from "https://deno.land/std/io/buffer.ts";

async function promptString(question) {
    console.log(question);

    for await (const line of readLines(Deno.stdin)) {
        return line;
    }
}

const userName = await promptString("Enter your name:");

Answer 4

I have a solution 100% pure Deno, but not intensively tested

async function ask(question: string = '', stdin = Deno.stdin, stdout = Deno.stdout) {
  const buf = new Uint8Array(1024);

  // Write question to console
  await stdout.write(new TextEncoder().encode(question));

  // Read console's input into answer
  const n = <number>await stdin.read(buf);
  const answer = new TextDecoder().decode(buf.subarray(0, n));

  return answer.trim();
}

const answer = await ask(`Tell me your name? `);
console.log(`Your name is ${answer}`);

Parts of the above code was taken from answer of Kevin Qian

Answer 5

I would suggest using the Input-Deno module. This is an example from the docs:

// For a single question:
const input = new InputLoop();
const nodeName = await input.question('Enter the label for the node:');
        
// output:
        
// Enter the label for the node:
        
// Return Value:
// 'a'

Answer 6

I have a small terminal sample to test with the Deno TCP echo server. It's something like:

private input = new TextProtoReader(new BufReader(Deno.stdin));

while (true) {
    const line = await this.input.readLine();
    if (line === Deno.EOF) {
        console.log(red('Bye!'));
        break;
    } else {
        // display the line
    }
}

The full project is on Github.