Python How to get stdout after running os system

Question

I want to get the stdout in a variable after running the os system call   Lets take this line as an example    batcmd  dir  result   os system batcmd    result will contain the error code  stderr 0 under Windows or 1 under some linux for the above example    How can I get the stdout for the above command without using redirection in the executed command

User · Answer

import subprocess string  echo Hello world  result subprocess getoutput string  print  result      result

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commands also works   import commands batcmd    dir  result   commands getoutput batcmd  print result   It works on linux  python 2 7

User · Answer

I had to use os system  since subprocess was giving me a memory error for larger tasks  Reference for this problem here  So  in order to get the output of the os system command I used this workaround   import os  batcmd    dir  result code   os system batcmd      gt  output txt   if os path exists  output txt        fp   open  output txt    r       output   fp read       fp close       os remove  output txt       print output

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I would like to expand on the Windows solution  Using IDLE with Python 2 7 5  When I run this code from file Expts py   import subprocess r   subprocess check output  cmd exe dir  shell False   print r      in the Python Shell  I ONLY get the output corresponding to  cmd exe   the  dir  part is ignored  HOWEVER  when I add a switch such as  K or  C      import subprocess r   subprocess check output  cmd exe  K dir  shell False   print r      then in the Python Shell  I get all that I expect including the directory listing  Woohoo    Now  if I try any of those same things in DOS Python command window  without the switch  or with the  K switch  it appears to make the window hang because it is running a subprocess cmd exe and it awaiting further input - type  exit  then hit  enter  to release  But with the  K switch it works perfectly and returns you to the python prompt  Allrightee then   Went a step further   I thought this was cool   When I instead do this in Expts py   import subprocess r   subprocess call  cmd exe dir  shell False   print r      a new DOS window pops open and remains there displaying only the results of  cmd exe  not of  dir   When I add the  C switch  the DOS window opens and closes very fast before I can see anything  as expected  because  C terminates when done   When I instead add the  K switch  the DOS window pops open and remain  AND I get all the output I expect including the directory listing   If I try the same thing  subprocess call instead of subprocess check output  from a DOS Python command window  all output is within the same window  there are no popup windows  Without the switch  again the  dir  part is ignored  AND the prompt changes from the python prompt to the DOS prompt  since a cmd exe subprocess is running in python  again type  exit  and you will revert to the python prompt   Adding the  K switch prints out the directory listing and changes the prompt from python to DOS since  K does not terminate the subprocess  Changing the switch to  C gives us all the output expected AND returns to the python prompt since the subprocess terminates in accordance with  C   Sorry for the long-winded response  but I am frustrated on this board with the many terse  answers  which at best don t work  seems because they are not tested - like Eduard F s  response above mine which is missing the switch  or worse  are so terse that they don t help much at all  e g    try subprocess instead of os system      yeah  OK  now what      In contrast  I have provided solutions which I tested  and showed how there are subtle differences between them  Took a lot of time but    Hope this helps

User · Answer

These answers didn t work for me  I had to use the following   import subprocess p   subprocess Popen   pwd    stdout subprocess PIPE  out   p stdout read   print out   Or as a function  using shell True was required for me on Python 2 6 7 and check output was not added until 2 7  making it unusable here    def system call command       p   subprocess Popen  command   stdout subprocess PIPE  shell True      return p stdout read

User · Answer

If all you need is the stdout output  then take a look at subprocess check output     import subprocess  batcmd  dir  result   subprocess check output batcmd  shell True    Because you were using os system    you d have to set shell True to get the same behaviour  You do want to heed the security concerns about passing untrusted arguments to your shell   If you need to capture stderr as well  simply add stderr subprocess STDOUT to the call   result   subprocess check output  batcmd   stderr subprocess STDOUT    to redirect the error output to the default output stream   If you know that the output is text  add text True to decode the returned bytes value with the platform default encoding  use encoding       instead if that codec is not correct for the data you receive

[python] Python: How to get stdout after running os.system?

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