Track error of subprocess and failures

Question

I'm maintaining a Perforce server via a Unix executable which logs the errors in the terminal whenever something happens to it. What I would like to do is use Python to start the executable, and then have it watch for any errors being logged in the terminal window from the application it's executing.

The following code works for execution, but I have no idea how to get data back from the subprocess when it gets logged to the terminal via some form of callback.

import subprocess
subprocess.call(["./p4d"])

score 1 · Answer 1 · answered Jun 04 '17 at 17:03

1

I usually do it this way

from subprocess import Popen, PIPE
proc = Popen(["./p4d"], stdout=PIPE, stderr=PIPE)
out, err = pipe.communicate()

pipe.communicate() will hang until the process is finished and then returns stdout and stderr

answered Jun 04 '17 at 17:03

J. Darnell

519
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Will this log errors as they occur, or just when the process exits? – James Ives Jun 04 '17 at 17:32
You get all of the logs but only once the process ends. Reading stdout/stderr while the process is running is a little bit trickier. – J. Darnell Jun 04 '17 at 17:40
1

https://stackoverflow.com/questions/2804543/read-subprocess-stdout-line-by-line might be helpful – J. Darnell Jun 04 '17 at 17:41

score 0 · Answer 2 · answered Jun 04 '17 at 17:40

process.stdout and process.stdout are file-like objects that you can read from. Assuming things are logged to stdout:

proc = Popen(['./p4d'], stdout=PIPE, encoding='utf-8')  # Or whatever encoding suits
for line in proc.stdout:
    # Note that line will end in `\n`, unless it is the last line.
    line = line.rstrip('\n')

    # Do something depending on the line

Track error of subprocess and failures

2 Answers2