[Tutor] os command

[Johan Geldenhuys]

Hugo,

I see that 'os.execcvp()' doesn't actually make two seperate processes. 
The advice you gave me works good. I just had to fgure out with what 
params I should call it. I'm still a bit unsure of how to call the sysem 
command with more than one argument.
This is what I have working now:
"""

import os, signal, time
pid = os.fork()
print 'pid; ',pid
if pid == 0: #child process
      
       #os.execvp('tcpdump', ['tcpdump', '-i modem0 > cap1.txt'])
       os.execvp('ping', ['ping', '127.0.0.1 -c 30 > cap.txt'])
      
time.sleep(5)
kill(pid)

def kill(pid, signal=signal.SIGTERM):
    print "trying to kill pid...", pid
    os.kill(pid, signal)
    os.waitpid(pid, 0)
    print "Killed %d"%pid
"""

The ping command is executed but the part where it must put the replies 
in the file is not recognized. How do I use the addisional arguments to 
be seen?

Thanks,

Johan
Hugo González Monteverde wrote:

> In UNIX, you use the fork() exec() technique for starting a new 
> process,  from the very first process(init) onwards. The os.system() 
> uses  a shell
> to do that, or you may do it yourself (in your script)
>
> A "command" is just an executable file running(process), unless you've 
> got a library function that does just that, then you could do what you 
> must without creating a new process.
>
> Probably your best bet would be to use the subprocess module. It was 
> designed around the limitations of the previous methods.
>
> Take a look at what oyu can do with it at:
>
> http://www.python.org/doc/2.4.2/lib/module-subprocess.html
>
> For example, the pid of the command would be available at the pid 
> atribute of a subprocess instance.
>
> p.pid
>
> Hugo   
>
> Johan Geldenhuys wrote:
>
>> Sorry for the late reply,
>> But is it necessary to use a child process? I don't want to execute 
>> the command in another process. What happens with the parent process 
>> and how do I execute my command in the parent process?
>>
>> Thanks
>>
>> Hugo González Monteverde wrote:
>>
>>> Hi,
>>>
>>> os.system will return the errorval of the application. You need to
>>>
>>> 1) get the pid of the child process
>>> 2) kill it using os.kill(os.SIGTERM)
>>> 3) reap the killed process
>>>
>>> This is all in unix/linux, of course.
>>>
>>> what I do (untested, please check order of args and correct usage of 
>>> exec):
>>>
>>> pid = os.fork()
>>>
>>> if pid == 0: #child process
>>>     os.execvp("tcpdump", "tcpdump", "-n",  "-i",  "eth0")
>>>
>>> else:   #parent
>>>     time.sleep(5)
>>>     os.kill(pid, os.SIGTERM)
>>>     os.waitpid(pid, 0)   #wait for process to end
>>>
>>>
>>>
>>> Johan Geldenhuys wrote:
>>>
>>>> I have script that calls a system command that I want to run for 5 
>>>> minutes.
>>>> """
>>>> import os
>>>> cmd = 'tcpdump -n -i eth0'
>>>> os.system(cmd)
>>>> """
>>>>
>>>> I can start a timer after the cmd is issued, but I don't know how 
>>>> to send a control signal to stop the command after I issued it. 
>>>> This is normally from the shell  ^c.
>>>>
>>>> This cmd my run in more than one thread on different interfaces and 
>>>> I don't whant all of then stopped at once. I think the best way is 
>>>> to make a thread for each interface where the cmd can be issued and 
>>>> stopped without the danger of stopping he wrong thread.
>>>>
>>>> Can anybody help?
>>>>
>>>> Thanks
>>>>
>>>> Johan
>>>> _______________________________________________
>>>> Tutor maillist  -  Tutor at python.org
>>>> http://mail.python.org/mailman/listinfo/tutor
>>>>
>>>
>>
>