transform-stream.js

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

var ts = new stream.Transform();

ts._transform = function(chunk, enc, cb) {
  // 'chunk' is the data from the readable source
  //
  // 'this.push(whatever)' or callback(err, whatever) writes
  // to target writeable
  cb(null, chunk.toString().toUpperCase());
}

ts.on('pipe', function (src) {
  src.on('end', function () {
    ts.push('\n\ntrailer!');
  });
});

fs.createReadStream('./stream-test.js')
  .pipe(ts, {end : false})
  .pipe(process.stdout);