How can I respond to a prompt in os.system?

Question

I'm trying to do something like this:

from subprocess import Popen
p = Popen(["vagrant", "ssh", "vmname", "-c", '"pvcreate -ff /dev/sdb"'])

But it requires user input. Also, that didn't work anyway. They give the error: bash: pvcreate -ff /dev/sdb: command not found, because it's looking for a program pvcreate -ff /dev/sdb, instead of pvcreate with arguments. I also tried this first:

p = Popen(["vagrant", "ssh", "vmname", "-c", "pvcreate", "-ff", "/dev/sdb"])

And have resorted to using this:

os.system("vagrant ssh vmname -c 'pvcreate -ff /dev/sdb'")

However I need to say yes when it prompts me. I've already tried these options as well:

os.system("yes | vagrant ssh vmname -c 'pvcreate -ff /dev/sdb'")
os.system("echo y | vagrant ssh vmname -c 'pvcreate -ff /dev/sdb'")

Is it possible to respond to a prompt using os.system?

Answer 1

I'd suggest using the list form of invocation.

import subprocess
command = ["vagrant", "ssh", "vmname", "-c", "pvcreate -ff /db/sdb"]
output,error  = subprocess.Popen(
                command, universal_newlines=True,
                stdout=subprocess.PIPE,  
                stderr=subprocess.PIPE).communicate()

This represents the set of parameters that are going to be passed and eliminates the need to mess around with shell quoting.