Read from stdin
Command line tools that work in pipelines read their input from stdin. Try this example with some piped input, for instance: echo "hello" | deno run https://docs.deno.com/examples/scripts/reading_stdin.ts
For interactive prompts there are global helpers, no stream handling needed. (They return null when stdin is not a terminal.)
if (Deno.stdin.isTerminal()) {
const name = prompt("What is your name?");
console.log(`Hello, ${name}!`);
}To read all of stdin as a string, collect its readable stream with a Response. This waits until the input ends.
const input = await new Response(Deno.stdin.readable).text();
console.log(`Read ${input.length} characters`);For line-by-line processing, decode the byte stream into text and split it into lines with the standard library. This processes input as it arrives instead of waiting for the end, which suits large or endless pipelines.
import { TextLineStream } from "jsr:@std/streams";
async function processLines() {
const lines = Deno.stdin.readable
.pipeThrough(new TextDecoderStream())
.pipeThrough(new TextLineStream());
for await (const line of lines) {
console.log(`line: ${line}`);
}
}Code written for Node.js reads process.stdin, which works in Deno too. It is an async iterable of chunks, already decoded when you set an encoding.
import process from "node:process";
async function readAllNodeStyle() {
process.stdin.setEncoding("utf8");
let data = "";
for await (const chunk of process.stdin) {
data += chunk;
}
return data;
}Note that a stream can only be consumed once: pick one of the approaches above per program run.
Run this example locally using the Deno CLI:
deno run https://docs.deno.com/examples/scripts/reading_stdin.ts