Unbale to fetch output from grep with pipe using python subprocess

Question

I am using the following command to fetch the CPU usage along with date and time. But I am getting only the CPU usage as output.

My code:

import subprocess
for i in range(3):
    cpu = (subprocess.Popen('top -bn2 -d1 | grep "Cpu\|average" ', shell=True, stdout=subprocess.PIPE).stdout)
    print(cpu, '----')

output:

  %Cpu(s):  7.3 us,  1.2 sy,  0.1 ni, 88.8 id,  2.5 wa,  0.0 hi,  0.1 si,  0.0 st
  %Cpu(s):  1.5 us,  0.2 sy,  0.0 ni, 98.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  --------
  %Cpu(s):  7.3 us,  1.2 sy,  0.1 ni, 88.8 id,  2.5 wa,  0.0 hi,  0.1 si,  0.0 st
  %Cpu(s):  2.7 us,  1.0 sy,  0.0 ni, 93.8 id,  2.5 wa,  0.0 hi,  0.0 si,  0.0 st
  --------
  %Cpu(s):  7.3 us,  1.2 sy,  0.1 ni, 88.8 id,  2.5 wa,  0.0 hi,  0.1 si,  0.0 st
  %Cpu(s):  3.8 us,  0.5 sy,  0.0 ni, 95.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

Expected Output:

 top - 12:58:07 up  2:37,  1 user,  load average: 0.61, 0.72, 0.58
  %Cpu(s):  7.3 us,  1.2 sy,  0.1 ni, 88.9 id,  2.5 wa,  0.0 hi,  0.1 si,  0.0 st
  top - 12:58:08 up  2:37,  1 user,  load average: 0.61, 0.72, 0.58
  %Cpu(s): 12.7 us,  2.0 sy,  0.0 ni, 78.3 id,  7.0 wa,  0.0 hi,  0.0 si,  0.0 st

Lê Tư Thành · Accepted Answer · 2019-11-08 08:45:06Z

Add read() and decode() like this, you will have what you want.

import subprocess
for i in range(3):
    cpu = (subprocess.Popen('top -bn2 -d1 | grep "Cpu\|average" ', shell=True, stdout=subprocess.PIPE).stdout)
    print(cpu.read().decode('utf-8'), '\n----')

output:

top - 15:43:00 up  7:36,  1 user,  load average: 0,97, 0,95, 1,28
%Cpu(s): 12,4 us,  3,1 sy,  0,0 ni, 84,1 id,  0,0 wa,  0,0 hi,  0,3 si,  0,0 st
top - 15:43:01 up  7:36,  1 user,  load average: 0,97, 0,95, 1,28
%Cpu(s):  5,9 us,  1,5 sy,  0,0 ni, 92,5 id,  0,0 wa,  0,0 hi,  0,2 si,  0,0 st

----
top - 15:43:01 up  7:36,  1 user,  load average: 0,97, 0,95, 1,28
%Cpu(s): 12,4 us,  3,1 sy,  0,0 ni, 84,1 id,  0,0 wa,  0,0 hi,  0,3 si,  0,0 st
top - 15:43:02 up  7:36,  1 user,  load average: 0,89, 0,94, 1,27
%Cpu(s):  2,1 us,  0,8 sy,  0,0 ni, 96,9 id,  0,0 wa,  0,0 hi,  0,2 si,  0,0 st

----
top - 15:43:02 up  7:36,  1 user,  load average: 0,89, 0,94, 1,27
%Cpu(s): 12,4 us,  3,1 sy,  0,0 ni, 84,1 id,  0,0 wa,  0,0 hi,  0,3 si,  0,0 st
top - 15:43:03 up  7:36,  1 user,  load average: 0,89, 0,94, 1,27
%Cpu(s):  4,1 us,  0,8 sy,  0,0 ni, 94,9 id,  0,0 wa,  0,0 hi,  0,2 si,  0,0 st

----

Pavan Skipo · Accepted Answer · 2019-11-08 08:59:20Z

0

The output of the stdout is of type BufferedReader, you need to either add .read() method or .communicate() to get proper string output, like :

cpu = (subprocess.Popen('top -bn2 -d1 | grep "Cpu\|average" ', shell=True, stdout=subprocess.PIPE).stdout).read()

or using communicate ( here you will also get errors )

cpu, err = subprocess.Popen('top -bn2 -d1 | grep "Cpu\|average" ', shell=True, stdout=subprocess.PIPE).communicate()

here is the output :

print(cpu.decode('utf-8'))
'top - 14:22:27 up  4:24,  1 user,  load average: 1.40, 1.72, 1.80\n%Cpu(s): 12.6 us,  3.2 sy,  1.8 ni, 59.9 id, 22.3 wa,  0.0 hi,  0.2 si,  0.0 st\ntop - 14:22:28 up  4:24,  1 user,  load average: 1.45, 1.72, 1.80\n%Cpu(s):  3.0 us,  2.5 sy,  0.0 ni, 83.6 id, 10.9 wa,  0.0 hi,  0.0 si,  0.0 st\n'

more info at docs : here

edited Nov 8, 2019 at 8:59

answered Nov 8, 2019 at 8:54

Pavan Skipo

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1 Comment

Dharshini Over a year ago

Thanks for clarifying my doubt

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