How can I tail a log file in Python?

by

Non Blocking

If you are on linux (as windows does not support calling select on files) you can use the subprocess module along with the select module.

import time
import subprocess
import select

f = subprocess.Popen(['tail','-F',filename],\
        stdout=subprocess.PIPE,stderr=subprocess.PIPE)
p = select.poll()
p.register(f.stdout)

while True:
    if p.poll(1):
        print f.stdout.readline()
    time.sleep(1)

This polls the output pipe for new data and prints it when it is available. Normally the time.sleep(1) and print f.stdout.readline() would be replaced with useful code.

Blocking

You can use the subprocess module without the extra select module calls.

import subprocess
f = subprocess.Popen(['tail','-F',filename],\
        stdout=subprocess.PIPE,stderr=subprocess.PIPE)
while True:
    line = f.stdout.readline()
    print line

This will also print new lines as they are added, but it will block until the tail program is closed, probably with f.kill().

More Related Contents:

  1. Get last n lines of a file, similar to tail
  2. How to implement a pythonic equivalent of tail -F?
  3. Head and tail in one line
  4. Convert a 3D array to RGB valued array [closed]
  5. How do I merge two dictionaries in a single expression (take union of dictionaries)?
  6. IndentationError: unindent does not match any outer indentation level
  7. Verify host key with pysftp
  8. Python: Find in list
  9. How to use subprocess popen Python [duplicate]
  10. dynamically add field to a form
  11. Most efficient way of making an if-elif-elif-else statement when the else is done the most?
  12. how to run python script without typing ‘python …’
  13. What do I use for a max-heap implementation in Python?
  14. How do I implement option buttons and change the button color in PyGame?
  15. Why are python strings and tuples are made immutable?
  16. Can I use a multiprocessing Queue in a function called by Pool.imap?
  17. How to change the tables’ fontsize with matplotlib.pyplot
  18. Convert fraction to float?
  19. ‘virtualenv’ won’t activate on Windows
  20. figure of imshow() is too small
  21. Turn Pandas Multi-Index into column
  22. Get root path of Flask application
  23. Loading UTF-8 file in Python 3 using numpy.genfromtxt
  24. Why switching to alert through selenium is not stable?
  25. What does ** (double star/asterisk) and * (star/asterisk) do for parameters in Python?
  26. How to get the return value of a function passed to multiprocessing.Process?
  27. How to connect a progress bar to a function?
  28. Dump stacktraces of all active Threads
  29. run python script directly from command line
  30. How to click on Load More button within Google Trends and print all the titles through Selenium and Python

Leave a Comment