progress_bar.rb

class ProgressBar
  def initialize(units=60)
    @units = units.to_f
  end

  def print(completed, total)
    norm     = 1.0 / (total / @units)
    progress = (completed * norm).ceil
    pending  = @units - progress
    Kernel.print "[#{'=' * progress }#{' ' * ( pending )}] #{percentage(completed, total)}%\r"
  end

  def percentage(completed, total)
    ( ( completed / total.to_f ) * 100 ).round
  end
end

# Usage:
#
# bar = ProgressBar.new
# bar.print(50, 100)
#
# => [==============================                              ] 50%