#!/usr/bin/python2.7
# vim:ai:et:ts=4:sw=4:wm=0:encoding=utf8:fileencoding=utf8
"""
tail.py
=======
Exports 'follow', which yields linewise the content being added
to a text file, similar to unix' "tail -f" functionality.
As a demonstration, you can run this script directly with an
argument, the filename you wish to follow. I use it to follow
my httpd logs:
$ python2.7 tail.py /var/log/httpd/access_log
....
"""
__all__ = ('follow',)
import time
def follow(stream):
"Follow the live contents of a text file."
line = ''
for block in iter(lambda:stream.read(1024), None):
if '\n' in block:
# Only enter this block if we have at least one line to yield.
# The +[''] part is to catch the corner case of when a block
# ends in a newline, in which case it would repeat a line.
for line in (line+block).splitlines(True)+['']:
if line.endswith('\n'):
yield line
# When exiting the for loop, 'line' has any remaninig text.
elif not block:
# Wait for data.
time.sleep(1.0)
# The End.
if __name__ == '__main__':
# As a simple demonstration, run it with the filename to tail.
import sys
with open(sys.argv[1], 'rt') as following:
following.seek(-64, 2)
try:
for line in follow(following):
sys.stdout.write(line)
except KeyboardInterrupt:
pass
# Fin.
