multistreams-through.js

var fs = require("fs"),
    split = require("split"),
    through2 = require("through2");

var destinations = {};

fs.createReadStream("all.txt",{encoding:"utf8"})
  .pipe(split())
  .pipe(through2({decodeStrings:false},transform,flush));

function transform(row, enc, callback) {

  getDestination(row[3]).write(row + "\n","utf8",callback);

}

function flush() {

  // unnecessary?
  for (var char in destinations) {
    destinations[char].end();
  }

}

function getDestination(char) {

  if (!destinations[char]) {
    destinations[char] = fs.createWriteStream(char + ".txt");
  }

  return destinations[char];

}