1

I am using Python( OSX Python 2.7.10) to ssh into a Debian box ( Python 2.7.9), then I run a bash script (./capture). The bash script contains some tcpdump commands. The problem I cant figure out is how to display the live results from the running bash script on the terminal. 

#!/usr/bin/env python3
import subprocess, os
output = subprocess.run(["ssh", "ju@192.168.199.125", "sudo ./capture"])
print(output)

I am able to ssh , and run the script successfully, but I get no output. When I hit CTRL C I get the following trace:

**^CTraceback (most recent call last):
  File "/Users/junesjoseph/run.py", line 3, in <module>
    output = subprocess.run(["ssh", "junes@192.168.199.125", "sudo ./capture"])
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/subprocess.py", line 405, in run
    stdout, stderr = process.communicate(input, timeout=timeout)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/subprocess.py", line 835, in communicate
    self.wait()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/subprocess.py", line 1457, in wait
    (pid, sts) = self._try_wait(0)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/subprocess.py", line 1404, in _try_wait
    (pid, sts) = os.waitpid(self.pid, wait_flags)
KeyboardInterrupt**

Any help is greatly appreciated. thanks

Gilles Quénot
  • 173,512
  • 41
  • 224
  • 223
cbr654
  • 11
  • 2

1 Answers1

2

The object returned by subprocess.run is a CompletedProcess object which has attributes which contain the stdout and stderr of the completed process. You don't want to print it directly, but you can use it to fetch the attribute you want to print.

import subprocess  # no reason to import os
subssh = subprocess.run(["ssh", "ju@192.168.199.125", "sudo ./capture"],
    # Set up for capturing stdout and stderr
    stdout=subprocess.PIPE, stderr=subprocess.PIPE,
    # Add commonly useful attributes
    check=True, universal_newlines=True)
print(subssh.output)

If you really only want the output to be displayed on standard output, capturing it so you can print it is basically superfluous. Just set it up to display directly, simply by not setting stdout or stderr to anything:

subssh = subprocess.run(["ssh", "ju@192.168.199.125", "sudo ./capture"],
    # Don't set up for capturing -- leave stdout and stderr alone
    check=True, universal_newlines=True)

Perhaps see also Running Bash commands in Python where I have posted a more detailed answer about common problems with subprocess.

tripleee
  • 175,061
  • 34
  • 275
  • 318