How to use `subprocess` command with pipes

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How to use `subprocess` command with pipes

I want to use subprocess.check_output() with ps -A | grep 'process_name'.
I tried various solutions but so far nothing worked. Can someone guide me how to do it?

Answer #1:

To use a pipe with the subprocess module, you have to pass shell=True.

However, this isn’t really advisable for various reasons, not least of which is security. Instead, create the ps and grep processes separately, and pipe the output from one into the other, like so:

ps = subprocess.Popen(('ps', '-A'), stdout=subprocess.PIPE)
output = subprocess.check_output(('grep', 'process_name'), stdin=ps.stdout)

In your particular case, however, the simple solution is to call subprocess.check_output(('ps', '-A')) and then str.find on the output.

Answered By: Taymon

Answer #2:

Or you can always use the communicate method on the subprocess objects.

cmd = "ps -A|grep 'process_name'"
ps = subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
output = ps.communicate()[0]

The communicate method returns a tuple of the standard output and the standard error.

Answered By: jkalivas

Answer #3:

See the documentation on setting up a pipeline using subprocess:

I haven’t tested the following code example but it should be roughly what you want:

query = "process_name"
ps_process = Popen(["ps", "-A"], stdout=PIPE)
grep_process = Popen(["grep", query], stdin=ps_process.stdout, stdout=PIPE)
ps_process.stdout.close()  # Allow ps_process to receive a SIGPIPE if grep_process exits.
output = grep_process.communicate()[0]
Answered By: AlcubierreDrive

Answer #4:

You can try the pipe functionality in

import sh
print sh.grep("-ax"), "process_name")
Answered By: amoffat

Answer #5:

Also, try to use 'pgrep' command instead of 'ps -A | grep 'process_name'

Answered By: Shooe

Answer #6:

JKALAVIS solution is good, however I would add an improvement to use shlex instead of SHELL=TRUE. below im grepping out Query times

import subprocess
import shlex
cmd = "dig @ +notcp|grep 'Query'"
ps = subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
output = ps.communicate()[0]
Answered By: Daniel Smith

Answer #7:


import subprocess
ps =['ps', '-A'], check=True, capture_output=True)
processNames =['grep', 'process_name'],
                              input=ps.stdout, capture_output=True)
Answered By: anaken78

Answer #8:

command = "ps -A | grep 'process_name'"
output = subprocess.check_output(["bash", "-c", command])
Answered By: Brent

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