Exec: Display stdout "live"

javascript

child-process

stdout-streaming

node-js-streams

byAlex Kataev·Oct 25, 2024

No time to waste. Use Node.js spawn to run a command and stream output live:

const { spawn } = require('child_process');
const process = spawn('your-command', ['arg1', 'arg2']);

// Because dessert can't wait. Output seconds as they cook.
process.stdout.on('data', (data) => console.log(data.toString())); 

// To err is human. Outputting it, divine.
process.stderr.on('data', (data) => console.error(data.toString()));

// The end is only the beginning. Code after the proc ends.
process.on('exit', (code) => console.log(`Exited with code ${code}`));

This nimble snippet pins on the live data flow, logging stdout and stderr while the command cooks. It also catches the exit code when the oven dings.

Step aside exec, spawn is in vogue

See, child_process.spawn let us stream output like a concert live on your console. Unlike the less fashionable child_process.exec, it doesn't wait for the command to end before outputting. This swag makes spawn an absolute must for long commands or when you want instant output.

Downfall of exec and rise of spawn

Still betting on exec? There are times when the dice might roll against you:

Running a marathon: exec buffers the output until the end - a long, exhausting wait.
Instant updates: exec keeps silent until the breaking news is history.
Buffer nightmares: The walls of an overflowing buffer are a sight not worth risking.

Good news is, you can always switch to spawn and be a winner.

Plan B: send stdout to console

Not up for a change of heart? No worries, exec lets you directly pipe to the console:

const { exec } = require('child_process');
const child = exec('your-long-running-command');

// SOS! Redirect all stdout to console.
child.stdout.pipe(process.stdout); 

// Dump all errors to the console, because we all love honesty!
child.stderr.pipe(process.stderr);

Though spawn is the best suit for the red carpet, this is a jeans-and-t-shirt-quick-fix.

The power of streams

When continuous output streams come knocking, Node.js is there with the right tools. Here's how:

Node.js Streams: Go beyond just child_process. Unlock the power of streams and rule the world of I/O.
Bi-directional banter: Attach listeners to stdin, stdout, and stderr. Interact with child processes, even on first dates.
Real-time logging: Log outputs instantly. Ideal for monitoring those long-term commitments.

It's not just gabbing about output; it's about building a responsive system that nods at the right moments.

Stream for the win

A few tips & tricks to up your stream game:

Pipe Dreams: Use .pipe() to control the stream course. Handy for logging or mid-air data processing.
Transform: Implement custom logic in your streams. Great to spring a surprise transformation on data as it flows.
Errors be gone: Listen for error events to handle exceptions and keep unhappiness at bay.

Understanding and implementing these concepts can make you the 'Prom Queen' of Node.js processes and stdout handling.

explain-codes / Javascript / Exec: Display stdout "live"

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