SaltyCrane Blog

Notes on Python, Django, and web development on Ubuntu Linux

How to use python and popen4 to capture stdout and stderr from a command

Date: March 12, 2007 | Tags: processes, python

You can use popen to capture stdout from a command:

import os
stdout = os.popen("dir asdkfhqweiory")
print stdout.read()

And your output will be something like:

>>> ================================ RESTART ================================
 >>> 
  Volume in drive C has no label.
  Volume Serial Number is XXXXXXXX
 
  Directory of C:\Python25
 
 
 >>>

If you wanted the error message, popen won't give it to you. To capture both stdout and stderr, use popen4:

import os

(dummy, stdout_and_stderr) = os.popen4("dir asdkfhqweiory")
print stdout_and_stderr.read()

This will give you the following output (which includes the error message):

>>> ================================ RESTART ================================
 >>> 
  Volume in drive C has no label.
  Volume Serial Number is XXXXXXXX
 
  Directory of C:\Python25
 
 File Not Found
 
 >>>

See http://docs.python.org/lib/os-newstreams.html for more information.

How to use the bash shell with Python's subprocess module instead of /bin/sh — posted 2011-04-13
How to capture stdout in real-time with Python — posted 2009-10-12
How to get stdout and stderr using Python's subprocess module — posted 2008-09-23

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