Use StringIO as stdin with Popen

Question

I have the following shell script that I would like to write in Python (of course grep . is actually a much more complex command):

#!/bin/bash

(cat somefile 2>/dev/null || (echo 'somefile not found'; cat logfile)) \
| grep .

I tried this (which lacks an equivalent to cat logfile anyway):

#!/usr/bin/env python

import StringIO
import subprocess

try:
    myfile = open('somefile')
except:
    myfile = StringIO.StringIO('somefile not found')

subprocess.call(['grep', '.'], stdin = myfile)

But I get the error AttributeError: StringIO instance has no attribute 'fileno'.

I know I should use subprocess.communicate() instead of StringIO to send strings to the grep process, but I don't know how to mix both strings and files.

Answer 1

p = subprocess.Popen(['grep', '...'], stdin=subprocess.PIPE, 
                                      stdout=subprocess.PIPE)
output, output_err = p.communicate(myfile.read())