Why I am capturing subprocess output through stderr and not stdout?

Question

I am running PSExec tool through subprocess. If psexec (not the tool on the remote computer) fails to initiate, I need to break. Hence, I am capturing all the command prompt output in a file and parsing it:

logfile = file('Ocd_Log.txt','w')

try:

  process = subprocess.Popen(r'"C:\Program Files (x86)\PSTools\PsExec.exe" -s -i 1 -d -u administrator -p pwd \\10.200.20.20 cmd.exe /k "C:\Osprey_OCD_Daemon_xtensa_9.lnk"', stdout = subprocess.PIPE,stderr = subprocess.PIPE)

  for line in process.stderr:
    print ' '
    sys.stderr.write(line)
    logfile.write(line)
   process.wait()

The above code works good and captures all the command line to the logfile. But I am unable to understand why I need to capture the output through process.stderr and not process.stdout. Please let me know.

thefourtheye · Accepted Answer · 2015-03-05 12:02:20Z

1

The program choose stdout or stderr (in your case PsExec.exe, u cant fix it). In common, stderr is used for debug data, it is exactly what logfile is!

edited Mar 5, 2015 at 12:02

thefourtheye

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answered Mar 5, 2015 at 11:12

Mux

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2 Comments

ElmoVanKielmo Over a year ago

I wonder who downvoted this. This is just the truth. PsExec.exe writes to stderr and therefore the data is available on stderr only.

user3565150 Over a year ago

What I got is it depends on the process whether it will give output on stdout or stderr. For Psexec it is stderr and not stdout.

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