can't save text string

[branko316]

Hi, I'm working in the FreeBSD OS environment and using Python version 3.6.8.

I'm essentially trying to run a script that does the equivalent of the following FreeBSD command:
sysctl -a | grep "group level=\"2\"" -A 1

So, a sysctl command and then piping it to a grep command. Then, I'd like to parse the remaining output (text/string), capture it (in a variable?) and make decisions on it.

Below is my code where the first subprocess.Popen executes the FreeBSD sysctl command, and I pass the output to "p2" and then "grep it" and pass that to p3 and get the expected output text -- see below.

But, I can't save this text/string to a variable so to parse it further.

So, first here is sysctl run at the FreeBSD command line and the associated output...
# sysctl -a | grep "group level=\"2\"" -A 1
<group level="2" cache-level="3">
<cpu count="8" mask="ff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7</cpu>
--
<group level="2" cache-level="3">
<cpu count="8" mask="ff00,0,0,0">8, 9, 10, 11, 12, 13, 14, 15</cpu>

Then, here's my Python code:

def sysctl_command():
   p1 = subprocess.Popen(['sysctl','-a'], stdout=subprocess.PIPE)
   p2 = subprocess.Popen(['grep', 'group level="2"', "-A 1"], stdin=p1.stdout, stdout=subprocess.PIPE)
   p3 = subprocess.Popen(['grep', 'cpu count'], stdin=p2.stdout)
   p1.stdout.close()
   p2.stdout.close()
   output, err  = p3.communicate()
   return output

#sysctl_command()
out = sysctl_command()
print (out)

and output...

Output:
# python ./mlnx_tune_freebsd.py
    <cpu count="8" mask="ff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7</cpu>
    <cpu count="8" mask="ff00,0,0,0">8, 9, 10, 11, 12, 13, 14, 15</cpu>
None

You'll notice that I tried to print 'out' variable and get "None" as opposed to the text string that is displayed to the screen.

Any thoughts as so what I might be doing wrong?

Thanks!