check output from CalledProcessError

Question

I am using subprocess check output from pythons subprocess module to execute a ping command  Here is how I am doing it   output   subprocess check output   ping   -c 2 -W 2   1 1 1 1     It is raising a CalledProcessError and says the output is one of the arguments of the function  Can anyone help me how to read that output  I would like to read the output into a string and parse it  So say for example if the ping returns      100  packet loss   I need to capture that  If there is any other better way  please suggest  Thanks

User · Answer

If you want to get stdout and stderr back (including extracting it from the CalledProcessError in the event that one occurs), use the following:

import subprocess

command = ["ls", "-l"]
try:
    output = subprocess.check_output(command, stderr=subprocess.STDOUT).decode()
    success = True 
except subprocess.CalledProcessError as e:
    output = e.output.decode()
    success = False

print(output)

This is Python 2 and 3 compatible.

If your command is a string rather than an array, prefix this with:

import shlex
command = shlex.split(command)

User · Answer

Thanx  krd  I am using your error catch process  but had to update the print and except statements  I am using Python 2 7 6 on Linux Mint 17 2   Also  it was unclear where the output string was coming from  My update   import subprocess    Output returned in error handler try      print  Ping stdout output on success  n                subprocess check output   ping    -c    2    -w    2    1 1 1 1     except subprocess CalledProcessError as e      print  Ping stdout output on error  n    e output     Output returned normally try      print  Ping stdout output on success  n                subprocess check output   ping    -c    2    -w    2    8 8 8 8     except subprocess CalledProcessError as e      print  Ping stdout output on error  n    e output    I see an output like this   Ping stdout output on error  PING 1 1 1 1  1 1 1 1  56 84  bytes of data   --- 1 1 1 1 ping statistics --- 2 packets transmitted  0 received  100  packet loss  time 1007ms   Ping stdout output on success  PING 8 8 8 8  8 8 8 8  56 84  bytes of data  64 bytes from 8 8 8 8  icmp seq 1 ttl 59 time 37 8 ms 64 bytes from 8 8 8 8  icmp seq 2 ttl 59 time 38 8 ms  --- 8 8 8 8 ping statistics --- 2 packets transmitted  2 received  0  packet loss  time 1001ms rtt min avg max mdev   37 840 38 321 38 802 0 481 ms

User · Answer

I ran into the same problem and found that the documentation has example for this type of scenario  where we write STDERR TO STDOUT and always exit successfully with return code 0  without causing catching an exception   output   subprocess check output  ping -c 2 -W 2 1 1 1 1  exit 0   stderr subprocess STDOUT  shell True    Now  you can use standard string function find to check the output string output

User · Answer

In the list of arguments  each entry must be on its own  Using  output   subprocess check output   ping    -c   2    -W   2    1 1 1 1      should fix your problem

User · Answer

This will return true only if host responds to ping  Works on windows and linux  def ping host               Returns True if host  str  responds to a ping request      NB on windows ping returns true for success and host unreachable             param    -n  if platform system   lower     windows  else  -c      result   False     try          out   subprocess check output   ping   param   1   host            ping exit code 0         if  Reply from     format host  in str out               result   True               except  subprocess CalledProcessError           ping exit code not 0             result   False      print str out       return result

User · Answer

According to the Python os module documentation os popen has been deprecated since Python 2 6   I think the solution for modern Python is to use check output   from the subprocess module   From the subprocess Python documentation      subprocess check output args     stdin None  stderr None  shell False  universal newlines False    Run command with arguments and return its output as a byte string       If the return code was non-zero it raises a CalledProcessError  The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute    If you run through the following code in Python 2 7  or later    import subprocess  try      print subprocess check output   ping    -n    2    -w    2    1 1 1 1    except subprocess CalledProcessError  e      print  Ping stdout output  n   e output   You should see an output that looks something like this   Ping stdout output   Pinging 1 1 1 1 with 32 bytes of data  Request timed out  Request timed out   Ping statistics for 1 1 1 1  Packets  Sent   2  Received   0  Lost   2  100  loss     The e output string can be parsed to suit the OPs needs    If you want the returncode or other attributes  they are in CalledProccessError as can be seen by stepping through with pdb   Pdb  dir e          class        delattr        dict        doc        format         getattribute        getitem        getslice        hash        init         module        new        reduce        reduce ex        repr         setattr        setstate        sizeof        str        subclasshook          unicode        weakref      args    cmd    message    output    returncode

[python] check output from CalledProcessError

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