popen help

Jason Zheng jzheng at jpl.nasa.gov
Fri Nov 12 21:19:08 CET 2004

exarkun at intarweb.us wrote:
> On Fri, 12 Nov 2004 11:29:46 -0800, Jason Zheng <jzheng at jpl.nasa.gov> wrote:
>>I'm trying to open a subshell to run some csh commands, and I want to 
>>connect the stdout of the subshell to the main stdout:
>>sub = Popen4('csh -f')
>>sub.tochild.write('source source.me\n')
>>for x in sub.fromchild.readlines():
>>   print x
>>>>import os, time
>>>>for x in iter(os.popen('for x in `seq 3`; do echo $x; sleep 1; done').readline, ''):
> ...     print time.time(), x,
> ... 
> 1100290304.55 1
> 1100290305.56 2
> 1100290306.56 3
>   The difference is that readline() returns one line whereas readlines() returns all of the lines.  Since you cannot know what all the lines are until you have read all of the data, it cannot return until the child process exits.
>   Jp

I doubt that's gonna resolve the problem I have tho. Suppose I send one 
command which doesn't not have the 'sleep' but prints some output line 
periodically, wouldn't I have to wait till the end of the execution to 
see any output?

Can I just connect sys.stdout to the stdout of the subshell?


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