The things you have to do to process stdin line-by-line in Node.js and it still blows up this process' memory over blocking whatever's connected to stdin.

gistfile1.js

var readline = require('readline')

var ch = []
  , closed = false
  , rl = readline.createInterface({
        input: process.stdin
      , output: process.stdout
      , terminal: false
    })

rl.on('close', function () { closed = true })
rl.on('error', function (error) {
    console.error(error)
    process.exit(1)
})
rl.on('line', ch.push.bind(ch))

function work() {
    var input = ch.shift()
    if (typeof input === 'undefined') {
        if (closed) {
            return
        }
        return process.nextTick(work)
    }
    asyncWork(input, function (error, output) {
        if (error) {
            console.error(error)
            process.exit(1)
        }
        process.stdout.write(output)
        process.nextTick(work)
    })
}
work()

function asyncWork(input, f) {
    process.nextTick(function () { f(undefined, input.toUpperCase()) })
}