Subprocess: get stdout from sigle line

Question

Being a Python noob I need to run a third party application (which writes its stdout into single line, they probably use something like skip_eol=True), from within my python script and display the app's stdout live.

This

process = subprocess.Popen(cmd, stdout=subprocess.PIPE)
for line in iter(process.stdout.readline, b''):
    print line.rstrip()

only allows me to get the stdout once the child process completed. I don't clearly understand how do I catch the entire stdout?

Are you sure the output of your `cmd` is a binary file? – Riccardo Petraglia Nov 15 '16 at 06:52 — Riccardo Petraglia, Nov 15 '16 at 06:52

Riccardo Petraglia · Answer 1 · 2016-11-15T13:20:10.740

0

Try like that:

#!/usr/bin/env python2

import subprocess
import shlex

process = subprocess.Popen(shlex.split('./bash_1_line_per_second.sh'), stdout=subprocess.PIPE)

while process.poll() is None:
    print 'reading' # Just to understand better what is happening
    print process.stdout.read(1)

This reads one character at time... is the output of cmd binary? In that case this probably wont work...

If you provide the output of cmd I can be more precise! In particular, if you need help to rebuild the line from the single characters.

This is the bash script I used to test:

#!/bin/bash

counter=0
while [[ "a" == "a" ]]; do
  echo -n "This is the line number $counter"
  let counter+=1
  sleep 1
  if [[ $counter -eq 5 ]]; then 
      exit 0
  fi
done

edited Nov 15 '16 at 13:20

answered Nov 15 '16 at 06:51

Riccardo Petraglia

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it still waits until the child process finishes – hdf Nov 15 '16 at 07:10
@hdf I edited the example to work as you required (I think) – Riccardo Petraglia Nov 15 '16 at 14:56
I'm getting `OSError: [Errno 13] Permission denied` so far trying to run the Python script you've provided. Looking for what might be causing it. Thanks. – hdf Nov 15 '16 at 17:54
Are you running your command or my bash script as subprocess? – Riccardo Petraglia Nov 15 '16 at 18:56
running your script – hdf Nov 15 '16 at 21:14
1

Then it is quite probably you did not make the script "executable". Use `chmod +x ` – Riccardo Petraglia Nov 15 '16 at 21:47
yeah, that was the case :) Now, however, I'm getting `AttributeError: 'list' object has no attribute 'read'` for `process = subprocess.Popen(shlex.split(cmd), stdout=subprocess.PIPE)` – hdf Nov 16 '16 at 06:23
could you post your `cmd`? If without `shlex.split` it works then do not use it... (it is only to create the list to use as command). Otherwise post all the error... – Riccardo Petraglia Nov 16 '16 at 07:04
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/128278/discussion-between-riccardo-petraglia-and-hdf). – Riccardo Petraglia Nov 16 '16 at 16:56

Subprocess: get stdout from sigle line

1 Answers1