parser

index.js

var fs = require('fs');
var readline = require('readline');

var file = process.argv[2];

if(!file) {
  console.log("Usage: \n\t node index.js file.txt");
  process.exit(1);
}

var lineparser = readline.createInterface({
  input: fs.createReadStream(file),
  output: process.stdout,
  terminal: false
});

lineparser.on('line', function(line) {
  var number = line.match(/([0-9]+)/);
  if(number[0] && number[0] < 10000) {
    console.log(line);
  }
});