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 cax | grep something` 

as in shell script?

Answer 1

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.

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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')) 

Answer 2

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.