"David" <da...@abbottdavid.com> wrote
I was playing around with trying to create a python program like tail -f
as discussed on the list. i came up with this;
Some general comments first:
def tail_it(bufsize=8192, linesep=__import__('os').linesep):
No idea why you are using the import stuff, just use os.linesep
f = None
if f == None:
This is redundant. You set f to None so the if test is always
true, so you don't need it.
f = open(tail_fname, 'rb')
Where is tail_fname defined? It would be sensible to make
it an input parameter.
f.seek(0, 2)
pos, tailsize = divmod(f.tell(), bufsize)
if tailsize == 0:
pos = max(0, pos-1)
pos *= bufsize
I got confused trying to work out exactly what this was doing.
pos is initially the number of times bufsize fits in the file, but
then gets modified to zero or one less than its current value.
f.seek(pos)
lines = f.read().split(linesep)
x = len(lines)
x = x-2
print lines[x:]
Could just be print lines[-2:]
f.close()
All of the above is repeated inside your while loop so
put it into a function and call the function inside the loop.
while True:
new_time = os.stat(tail_fname).st_mtime
if new_time > old_time:
Where is old_time defined?
You could call your new function here
f = open(tail_fname, 'rb')
f.seek(0, 2)
pos, tailsize = divmod(f.tell(), bufsize)
if tailsize == 0:
pos = max(0, pos-1)
pos *= bufsize
f.seek(pos)
lines = f.read().split(linesep)
x = len(lines)
x = x-2
print lines[x:]
time.sleep(sec_to_wait)
And call this after the function
f.close()
[output]
['May 5 22:32:26 opteron su[5589]: pam_unix(su:session): session closed
for user root', '']
['May 5 22:32:26 opteron su[5589]: pam_unix(su:session): session closed
for user root', '']
['May 5 22:40:01 opteron cron[22996]: (root) CMD (test -x
/usr/sbin/run-crons && /usr/sbin/run-crons )', '']
['May 5 22:41:26 opteron ntpd[3571]: kernel time sync status change
4001', '']
['May 5 22:41:26 opteron ntpd[3571]: kernel time sync status change
4001', '']
[/output]
That was with sec_to_wait set at 30
The problem I am having is it will print something whatever sec_to_wait
is set to even if the file's st_mtime is the same. I want it to only
prine when the st_mtime has changed. I think I need to update the while
loop and make old_time = new-time and start over but I need some
direction to get started, thanks
You need to set the old time somewhere, it never changes in your code.
If you put the actual read/print code in a function (it would be better not
to have the print in there, just return the string to be printed. Then your
code would look like:
import os
def get_tail(fname, bufsize, linesep):
f = open(fname, 'rb')
f.seek(0, 2)
pos, tailsize = divmod(f.tell(), bufsize)
if tailsize == 0:
pos = max(0, pos-1)
pos *= bufsize
f.seek(pos)
lines = f.read().split(linesep)
f.close()
return lines[-2:]
def tail_it(fname, bufsize=8192, linesep=os.linesep):
while True:
new_time = os.stat(tail_fname).st_mtime
if new_time > old_time:
time.sleep(sec_to_wait)
print get_tail (fname, bufsize, linesep)
old_time = new_time
I haven't tried it but that should be close to what you want.
--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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