nodejs_large_stdin.js

const fs = require('fs');
const buf = Buffer.allocUnsafe(400 * 1024 * 1024);
const regex = /your-pattern-here/g;
let leftover = Buffer.alloc(0);

while (true) {
  const bytesRead = fs.readSync(0, buf, 0, buf.length);
  if (bytesRead === 0) break;

  const current = Buffer.concat([leftover, buf.subarray(0, bytesRead)]);
  let end = (bytesRead === buf.length) ? current.lastIndexOf('\n') + 1 : current.length;
  if (end <= 0) end = current.length;

  const str = current.toString('utf8', 0, end);
  let match;
  while ((match = regex.exec(str)) !== null) console.log(match[0]);

  leftover = Buffer.from(current.subarray(end));
}

nodejs_readfile_by_400mb.js

const fs = require('fs');
const fd = fs.openSync('large_file.txt', 'r');
const size = fs.fstatSync(fd).size;
const buf = Buffer.allocUnsafe(400 * 1024 * 1024);
const regex = /your-pattern-here/g;

for (let offset = 0; offset < size; ) {
  const bytesRead = fs.readSync(fd, buf, 0, buf.length, offset);
  let end = (offset + bytesRead < size) ? buf.lastIndexOf('\n', bytesRead) + 1 : bytesRead;
  if (end <= 0) end = bytesRead; 

  const str = buf.toString('utf8', 0, end);
  let match;
  while ((match = regex.exec(str)) !== null) {
    console.log(match[0]);
  }

  offset += end;
}
fs.closeSync(fd);