How can I redirect the output of python logging statements to a file at run time using redirection?
I am using python 3.7 in Debian. When I redirect the output from a python script containing a print statement to a file, I get the expected result – a file containing the output.
If I use logging.debug to create the screen output and redirect this to a file, I get the output displayed on the screen and a zero size file.
python_test.py
print('hello')
python python_test.py > test.txt more test.txt hello
python_logging_test.py
import logging
logging.basicConfig(level=logging.DEBUG, format='%(message)s')
logging.debug('from logger')
python python_logging_test.py > test2.txt from logger ls -al test2.txt -rw-r--r-- 1 bart bart 0 Mar 31 20:00 test2.txt
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Answer
logging does not use the stdout stream, it uses the stderr output stream.
Redirect the stderr stream:
method 1
python python_logging_test.py 2> test2.txt
more test2.txt from logging
method 2
Use stdbuf:
stdbuf -e L python python_logging_test.py > test2.txt
more test2.txt from logger
from stdbuf –help -e, –error=MODE adjust standard error stream buffering If MODE is ‘L’ the corresponding stream will be line buffered.