How to run “ ps cax | grep something ” in Python?

Question

How do I run a command with a pipe | in it?

The subprocess module seems complex...

Is there something like

output,error = `ps ca         


        

Answer 1

Drop that 'ps' subprocess and back away slowly! :)

Use the psutil module instead.

Answer 2

import subprocess

process = subprocess.Popen("ps cax | grep something",
                             shell=True,
                             stdout=subprocess.PIPE,
                           )
stdout_list = process.communicate()[0].split('\n')

Answer 3

import os

os.system('ps -cax|grep something')

If you wanna replace grep argument with some variable:

os.system('ps -cax|grep '+your_var)

Answer 4

You've already accepted an answer, but:

Do you really need to use grep? I'd write something like:

import subprocess
ps = subprocess.Popen(('ps', 'cax'), stdout=subprocess.PIPE)
output = ps.communicate()[0]
for line in output.split('\n'):
    if 'something' in line:
        ...

This has the advantages of not involving shell=True and its riskiness, doesn't fork off a separate grep process, and looks an awful lot like the kind of Python you'd write to process data file-like objects.

Answer 5

See Replacing shell pipeline:

import subprocess

proc1 = subprocess.Popen(['ps', 'cax'], stdout=subprocess.PIPE)
proc2 = subprocess.Popen(['grep', 'python'], stdin=proc1.stdout,
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE)

proc1.stdout.close() # Allow proc1 to receive a SIGPIPE if proc2 exits.
out, err = proc2.communicate()
print('out: {0}'.format(out))
print('err: {0}'.format(err))

PS. Using shell=True can be dangerous. See for example the warning in the docs.

---

There is also the sh module which can make subprocess scripting in Python a lot more pleasant:

import sh
print(sh.grep(sh.ps("cax"), 'something'))