带有顶部的Python Popen空标准输出

Question

I try to measure CPU usage via top and python:

#!/usr/bin/python
import subprocess
from subprocess import PIPE, Popen

proc = subprocess.Popen("top -c -b -n 1 | grep /usr/local/bin/wineserver | grep -v grep | awk '{print $9}'", shell=True, stdout=PIPE, stderr=PIPE)
stdout, stderr = proc.communicate()

print len(stdout)
print len(stderr)

Output:

0

0

If I run the cmd via shell I get:

54

It seems the piping is the issue but I am not sure.

Solution:

os.system("top -c -b -n 1 | grep /usr/local/bin/wineserver | grep -v grep | awk '{print $9}' > top")

stdout = open("top").read().strip("\n")

Answer 1

When run interactively, top limits its display to your screen width. When run through Popen with stdout=PIPE , top is not running in a terminal and reverts to its default column width. This can be changed with an environment variable.

You could ditch the shell completely and process with python:

#!/usr/bin/python
import subprocess
from subprocess import PIPE, Popen
import os

myenv = os.environ.copy()
myenv["COLUMNS"] = "512"
proc = subprocess.Popen(["top", "-c", "-b", "-n", "1"], stdout=PIPE, stderr=PIPE, env=myenv)
for line in proc.stdout:
    columns = print line.strip().split()
    if columns[-1] == '/usr/local/bin/wineserver':
        print columns
proc.wait()

Alternately, you can get CPU information through ps and use its filtering and output format specifiers to just grab the information you want. Below I use filters to display CPU and command line for "wineserver" only.

#!/usr/bin/python
import subprocess
from subprocess import PIPE, Popen

proc = subprocess.Popen(["ps", "-ww", "--no-headers", "-C", "wineserver", "-o", "pcpu args"], 
    stdout=PIPE, stderr=PIPE, env=myenv)
for line in proc.stdout:
    pcpu, command = print line.strip().split(" ", 1)
    print pcpu, command
proc.wait()