fs/write

53.js

var fs = require('fs');

fs.open('./my_file_2.txt', 'a', function opened(err, fd) {
  if (err) { throw err; }
  var writeBuffer = new Buffer('writing this string'),
      bufferPosition = 0,
      bufferLength = writeBuffer.length, filePosition = null;

  fs.write(fd, writeBuffer, bufferPosition, bufferLength, filePosition, 
    function wrote(err, written) {
      if (err) { throw err; }
        console.log('wrote ' + written + ' bytes');
      }
  );
});