How to use `subprocess` command with pipes

Question

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

Answer 1

Using subprocess.run

import subprocess

ps = subprocess.run(['ps', '-A'], check=True, capture_output=True)
processNames = subprocess.run(['grep', 'process_name'], input=ps.stdout)
print(processNames.stdout)

Answer 2

You can try the pipe functionality in sh.py:

import sh
print sh.grep(sh.ps("-ax"), "process_name")

Answer 3

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)
ps.wait()

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

Answer 4

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]
print(output)

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

Answer 5

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

Answer 6

After Python 3.5 you can also use:

    import subprocess

    f = open('test.txt', 'w')
    process = subprocess.run(['ls', '-la'], stdout=subprocess.PIPE, universal_newlines=True)
    f.write(process.stdout)
    f.close()

The execution of the command is blocking and the output will be in process.stdout.