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pythongreppipesubprocesshead

Using subprocess to get output of grep piped through head -1

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.

Solution

  • 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()