Using subprocess to get output of grep piped throu

Question

This question already has an answer here:

• 'yes' reporting error with subprocess communicate() 3 answers
• How to use `subprocess` command with pipes 6 answers

The gist of what I'm trying to do is this:

grep -n "some phrase" {some file path} | head -1

I would like to pass the output of this into python. What I've tried so far is:

p = subprocess.Popen('grep -n "some phrase" {some file path} | head -1',shell=True,stdout=subprocess.PIPE)

I get back a lot of messages saying

"grep: writing output: Broken pipe"

I'm not very familiar with the subprocess module, I would like advice as to how to get this output, and what I am currently doing wrong.

Answer 1

The docs show you how to replace shell piping using Popen:

from subprocess import PIPE, Popen


p1 = Popen(['grep', '-n', 'some phrase', '{some file path}'],stdout=PIPE)
p2 = Popen(['head', '-1'], stdin=p1.stdout, stdout=PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
out,err = output = p2.communicate()

Answer 2

Let shell do it for you (lazy workaround):

import subprocess
p = subprocess.Popen(['-c', 'grep -n "some phrase" {some file path} | head -1'], shell=True, stdout=subprocess.PIPE)
out, err = p.communicate()
print out, err