popen help

[exarkun at intarweb.us]

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')
> sub.tochild.write('runthis\n')
> sub.tochild.close()
> 
> 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