使用子流程模块从Python执行命令行命令

Question

I am trying to use the subprocess module in python and trying to fetch the process id of firefox

cmd = "firefox &" 
fire = subprocess.Popen(cmd,shell=True, stdout=subprocess.PIPE, preexec_fn=os.setsid)
fire_task_procs = find_task(fire.pid)
print "fire_task_procs",fire_task_procs

I think I am getting the pid of the commandline argument that I am executing.. am I doing something wrong? I confirmed that it is not the same using the ps aux | grep firefox ps aux | grep firefox

Answer 1

If you use shell=True the pid you'll get ist that of the started shell, not that of the process you want, specially as you use & to send the process into background.

You should use the long (list) form of supplying the parameters, without & , as that makes little sense anyway if you combine it with output redirection.

Answer 2

Don't use the shell, instead just use

subprocess.Popen(['firefox'], stdout=subprocess.PIPE, preexec_fn=os.setsid)

However, if firefox is already running then this will not work either since in this case firefox will use some IPC to tell the existing process to open a new window and then terminates.