python中默认情况下是等待子进程完成之后，一下读取子进程的输出，要想逐行读取，需要自己做一点小技巧。

import sys,os,socket  import datetime  import fcntl  import subprocess  from threading import Thread    def log_worker(stdout):      ''' needs to be in a thread so we can read the stdout w/o blocking '''      username, hostname = os.environ.get('USER'), socket.gethostname()      log_file = '/var/log/mysql-%s.log' % username      log = open(log_file, 'a')      while True:          output = non_block_read(stdout).strip()          if output:              ''' [Tue Oct 30 22:13:13 2012 cseibert@host1]> '''              prompt = '[%(timestamp)s %(username)s@%(host)s]> \n' % dict(                      timestamp=datetime.datetime.now().strftime('%a %b %d %H:%M:%S %Y'),                      username=username,                      host=hostname)              print prompt + output              log.write(prompt + output + '\n')      log.close()    def non_block_read(output):      ''' even in a thread, a normal read with block until the buffer is full '''      fd = output.fileno()      fl = fcntl.fcntl(fd, fcntl.F_GETFL)      fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)      try:          return output.read()      except:          return ''    if __name__ == '__main__':      sub_process = subprocess.Popen(          ['sh', '/root/test/dummy.sh'],          stdin=sys.stdin,          stdout=subprocess.PIPE,          stderr=subprocess.PIPE)        thread = Thread(target=log_worker, args=[sub_process.stdout])      thread.daemon = True      thread.start()        sub_process.wait()      thread.join(timeout=1)