from subprocess import Popen, PIPE

def shell_exec(cmd, cb=None, poll=True):
  with Popen(cmd, stdout=PIPE, bufsize=1) as p:
    if poll:
      while p.poll() is None:
        line = p.stdout.readline().decode('utf-8').strip()
        if callable(cb): cb(line)
        time.sleep(0.5)
      
      for line in p.stdout.readlines():
        line = line.decode('utf-8').rstrip()
        if callable(cb): cb(line)
    else:
      pass