gistfile1.rb

require 'absolute_time'
last_checked = 0.0
thread = Thread.new do
  %x{ Shell command here }
end
while true
  now = AbsoluteTime.now.to_f
  if now.to_i > last_checked.to_i
    File.open('some-file.txt', 'a') { |f| f.write(0)}
    last_checked = now
  end
  break unless thread.status
  sleep(0.1)
end