strange subprocess behavior when calling ps

[James Mills]

On Wed, Nov 17, 2010 at 12:33 PM, Roger Davis <rbd at hawaii.edu> wrote:
> Hi all,
>
> I have encountered a strange problem with some code I am writing to
> search the system process list for certain running processes. I am
> using subprocess.Popen() to call '/bin/ps -e'. When I save my code to
> the file pid.py (whose first line is #!/usr/bin/python) and run it
> with the command
>
> % ./pid.py
>
> it works perfectly fine, retrieving lines from my pipe to the /bin/ps
> output which look exactly as if I had typed the command '/bin/ps -e'
> myself into a shell window. Here is a sample line from that output:
>
>  1891 ttys000    0:00.12 -tcsh
>
> Now for the weird part -- when I run this code using the command
>
> % python pid.py
>
> I get entirely different output. It only prints out a very few
> processes instead of the entire table, and each line also has lots of
> environment variable values displayed. Here is the line from that
> output which corresponds to the line immediately above:
>
>  1891 s000  S+     0:00.12 -tcsh PATH=/usr/bin:/bin:/usr/sbin:/sbin
> TMPDIR=/var/folders/3e/3e-TyTQIG-aOa4x37pbTbk++-H6/-Tmp-/ SHELL=/bin/
> tcsh HOME=/Users/hmrgsoft USER=hmrgsoft LOGNAME=hmrgsoft DISPLAY=/tmp/
> launch-c1YZNr/org.x:0 SSH_AUTH_SOCK=/tmp/launch-AJ9xbl/Listeners
> Apple_PubSub_Socket_Render=/tmp/launch-BsRx5Y/Render
> COMMAND_MODE=unix2003 __CF_USER_TEXT_ENCODING=0x532:0:0
> TERM_PROGRAM=Apple_Terminal TERM_PROGRAM_VERSION=273 LANG=en_US.UTF-8
> TERM=xterm-color
>
> It's like it's calling up an entirely different ps, or passing it
> different command arguments. In both cases, however, I am explicitly
> calling /bin/ps with the same -e argument, and there appear to be no
> other ps commands on my system, neither do I appear to have any ps
> builtin command in any shell.
>
> I am running 2.6.6 under MacOS 10.6.4 on a MacBook Pro Intel. I have
> appended the code below. I am running both commands directly in a
> Terminal window running tcsh.
>
> Can anyone explain this? Thanks!
>
> Roger Davis
>
> ##### code follows
>
> #!/usr/bin/python
> import sys
> import subprocess
>
> def main():
>
>        psargs= ["/bin/ps", "-e"]
>        try:
>                ps= subprocess.Popen(psargs, stdout=subprocess.PIPE, close_fds=True)
>                psout= ps.communicate()[0]
>                pslines= psout.splitlines()
>                for line in pslines:
>                        print "%s" % line
>        except KeyboardInterrupt:
>                print "Keyboard interrupt received -- terminating."
>                sys.stdout.flush()
>                sys.exit(-1)
>        except:
>                print "%s: unexpected error in generation of system process list" %
> prognm
>                sys.stdout.flush()
>                sys.exit(-1)
>
> main()

Roger, why not use the nicely written and documented psutil module ?

http://pypi.python.org/pypi/psutil/0.2.0
http://code.google.com/p/psutil/

cheers
James

-- 
-- James Mills
--
-- "Problems are solved by method"