Python `tee` stdout of child process

Is there a way in Python to do the equivalent of the UNIX command line tee? I'm doing a typical fork/exec pattern, and I'd like the stdout from the child to appear in both a log file and on the stdout of the parent simultaneously without requiring any buffering.

In this python code for instance, the stdout of the child ends up in the log file, but not in the stdout of the parent.

pid = os.fork()
logFile = open(path,"w")
if pid == 0:
  os.dup2(logFile.fileno(),1)  
  os.execv(cmd)

edit: I do not wish to use the subprocess module. I'm doing some complicated stuff with the child process that requires me call fork manually.

python file-io

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1 Answer

In the following, SOMEPATH is the path to the child executable, in a format suitable for subprocess.Popen (see its docs).

import sys, subprocess


f = open('logfile.txt', 'w')
proc = subprocess.Popen(SOMEPATH, stdout=subprocess.PIPE)

while True:
    out = proc.stdout.read(1)
    if out == '' and proc.poll() != None:
        break
    if out != '':
        # CR workaround since chars are read one by one, and Windows interprets
        # both CR and LF as end of lines. Linux only has LF
        if out != '\r': f.write(out)
        sys.stdout.write(out)
        sys.stdout.flush()

answered 2011-07-01T07:04:12.050

Python `tee` stdout of child process

1 Answer

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