A progress bar for Groovy

progress.groovy

def progressBar = { max, closure ->
  def template = "\r[%s] %s"
  def progress = 0
  def percent = 0
  def barLength = 100
  def progressRatio = barLength / 100

  while (progress < max) {
    def progressBuffer = new StringBuilder();
    def step = closure()
    if (!step) step = 1    // default to stepping 1
    if (step < 0) continue // no progress
    // else step is the amount of progress
    progress = Math.min(max, progress + step)
    percent        = (int) ((progress / max) * 100)
    progressLength = (int) ((progress / max) * (100 * progressRatio))

    progressBuffer.append('=' * progressLength)
    progressBuffer.append(' ' * (barLength - progressLength))

    print String.format(template, progressBuffer, "${percent}%")
  }
  println ''
}

progressBar 10, {
  sleep(500)
  //randomly return -1, 0, or 1
  def result = new Random().nextInt(3) - 1
}

This doesn't handle if the system terminal width is less than 100 (barLength). Unfortunately, such a luxury would require work that has already been done with the JCurses library.