progress_meter.rb

#!/usr/bin/ruby                                         

class ProgressMeter
  attr_accessor :progress, :total

  def initialize( total = 1 )
    @progress, @total = 0, total
    @old_str_size = 0           
  end                           

  def run( total = nil, &blk )
    @total = total  if total  
    @start_time = Time.now    

    $stdout.sync = true
    while @progress < @total do
      yield                    
      @progress += 1           
      update                   
    end                        
    puts                       
  end                          

protected
  def update
    if @progress >= @total
      print_in_place "done (#{total} over #{Time.now - @start_time}s)"
      return
    end

    eta = (Time.now - @start_time) * ((@total.to_f / @progress) - 1.0)
    print_in_place( '%i/%i (%.1f%%) ETA: %s' % [@progress, @total, 100.0 * @progress / @total, format_duration(eta)] )
  end

  def print_in_place( str )
    print( "\b" * @old_str_size, str )

    extra = @old_str_size - str.size
    print( ' ' * extra, "\b" * extra )  if extra > 0

    @old_str_size = str.size
  end

  # taken from ActiveSupport
  def format_duration( duration )
    distance_in_minutes = (duration.abs / 60).round
    distance_in_seconds = duration.abs.round

    case distance_in_minutes
      when 0..1
        case distance_in_seconds
          when 0..4   then 'less than 5 seconds'
          when 5..9   then 'less than 10 seconds'
          when 10..19 then 'less than 20 seconds'
          when 20..39 then 'half a minute'
          when 40..59 then 'less than 1 minute'
          else             '1 minute'
        end

      when 2..44           then "#{distance_in_minutes} minutes"
      when 45..89          then 'about 1 hour'
      when 90..1439        then "about #{(distance_in_minutes.to_f / 60.0).round} hours"
      when 1440..2879      then '1 day'
      when 2880..43199     then "#{(distance_in_minutes / 1440).round} days"
      when 43200..86399    then "about 1 month"
      when 86400..525599   then "#{(distance_in_minutes / 43200).round} months"
      when 525600..1051199 then "about 1 year"
      else                      "over #{(distance_in_minutes / 525600).round} years"
    end
  end
end

print 'Doing stuff ... '
ProgressMeter.new.run( 100 ) do
  sleep 0.1
end