random number from GPG key

rand.js

const { promisify } = require('util');
const exec = promisify(require('child_process').exec);

/** Returns a random byte as a floating-point decimal between 0 and 1. */
async function random() {
	const payload = await exec(`gpg-connect-agent "SCD RANDOM 1" /bye`);
	const randomBytes = payload.stdout.split('\n')[0].substr(2);

	const buffer = Buffer.from(randomBytes, 'utf-8');
	const number = buffer.readUIntBE(0, 1);
	return number;
}

(async () => {
	const lowerLimit = 1;
	const upperLimit = parseInt(process.argv[2], 10);

	let rand;
	do {
		rand = (await random()) + lowerLimit;
	} while (rand > upperLimit);

	console.log(rand);
})();