poor man's bi-directional sync

sync.js

#!/usr/bin/env node

// Sync two dirs giving precedence to the machine with the most recently modified files.
// After the first sync we sync again with the opposite precedence to make sure files
// deleted on either machine stay gone.
//
// The (primary) problem with this approach is that the newest changes always win. If
// you edit a file on both machines the latest changes will be the *only* remaining
// changes. Be careful if you actually use this!

var spawn = require('child_process').spawn
  , N = 2
  , Local = 0
  , Remote = 1
  , latestUpdates = []
  , localDir = process.argv[2]
  , remoteDir = process.argv[3]

if (!(localDir && remoteDir)) {
  console.warn('usage: sync.js <local> <remote>')
  process.exit(1)
}

function checkIfDone() {
  if (latestUpdates.length < N) return
  function done(e) { console.log(e ? 'fail' : 'ok') }
  if (latestUpdates[Local] > latestUpdates[Remote]) {
    sync(localDir, remoteDir, done)
  } else {
    sync(remoteDir, localDir, done)
  }
}

function sync(src, dest, cb) {
  var child = spawn('rsync', ['-avu', '--delete', src, dest])
    , out = []
    , err = []
  child.stdout.on('data', function(buf) { out.push(buf) })
  child.stderr.on('data', function(buf) { err.push(buf) })
  child.on('exit', function(code) {
    if (code !== 0) {
      console.warn('STDOUT:')
      console.warn(out.join('\n'))
      console.warn('STDERR:')
      console.warn(err.join('\n'))
      console.warn('!! sync failed with exit code ' + code)
    }
    cb(code !== 0)
  })
}

// mtime of most recently modified file with zsh: stat -f %m **/*(.om[1])

// find mtime of most recently modified local file
var local = spawn('zsh', ['-fc', 'cd \'' + localDir + '\'; stat -f %m **/*(.om[1])'])
local.stdout.on('data', function(buf) { latestUpdates[Local] = Number(buf.toString()) })
local.on('exit', checkIfDone)

// find mtime of most recently modified remote file
var parts = remoteDir.split(':')
  , host = parts[0]
  , dir = parts[1].replace('~', '$HOME')
  , remote = spawn('ssh', [host, 'zsh -fc "cd \'' + dir + '\'; stat -f %m **/*(.om[1])"'])
remote.stdout.on('data', function(buf) { latestUpdates[Remote] = Number(buf.toString()) })
remote.on('exit', checkIfDone)