trasnform.js

/**
 Convert data from `process.stdin` to upper-case data on `process.stdout`
 using the `through` module.

 through(write, end) returns a readable/writable stream and given `write` and
 `end` functions, both of which are optional.

 When you call `src.pipe(dst)` on some stream `dst` created with `through()`, the
 `write(buf)` function will be called when data from `src` is available.
 When `src` is done sending data, the `end()` function is called.

 Inside the `write` and `end` callbacks, `this` is set to the through stream
 returned by `through()` so you can just call `this.queue()` inside the callbacks
 to transform data.

 When you specify a falsy value for the `write` argument, this function is used
 to pass input data directly through to the output unmodified:

 function write (buf) { this.queue(buf) }

 The `this.queue(null)` tells the consuming stream to not expect any more data.

 The default `end` function is just:

 function end () { this.queue(null) }

 For example, here is a program that fires the `write(buf)` and `end()` callbacks
 by calling `.write()` and `.end()` manually:

 var through = require('through');
 var tr = through(write, end);
 tr.write('beep\n');
 tr.write('boop\n');
 tr.end();

 function write (buf) { console.dir(buf) }
 function end () { console.log('__END__') }

 Instead of calling `console.dir(buf)`, your code should use `this.queue()` in
 your `write()` function to output upper-cased data.

 Don't forget to feed data into your stream from stdin and output data from
 stdout, which should look something like:

 process.stdin.pipe(tr).pipe(process.stdout);

 Note that the chunks you will get from `process.stdin` are Buffers, not strings.
 You can call `buf.toString()` on a Buffer to get a string and strings can do
 `.toUpperCase()`.

 */

var through = require('through');

var write = function(data) {

	this.queue(data.toString().toUpperCase());
}

var tr = through(write);

process.stdin.pipe(tr).pipe(process.stdout);