PeterHarding at 06:09, 19 July 2009

2009-07-19T06:09:06Z

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	[[Category:Tools]]		[[Category:Tools]]
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PeterHarding: New page: =Script=

 #!/usr/bin/python  '''A module which implements a unix-like "tail" of a file. A callback is made for every new line found in the file.  Options specify whether the existing...

2008-05-27T04:19:29Z

New page: =Script= <pre> #!/usr/bin/python '''A module which implements a unix-like "tail" of a file. A callback is made for every new line found in the file. Options specify whether the existing...

New page

=Script=

<pre>
#!/usr/bin/python

'''A module which implements a unix-like "tail" of a file.
A callback is made for every new line found in the file. Options
specify whether the existing contents of the file should be read
or ignored.

@author Sean Reifschneider <jafo@tummy.com>
@version $Revision: 1.51 $

If a file is emptied or removed, the tail will continue reading lines
which are written in the new place.

Simple example:

import tail

def callback(line):
print 'Line: "%s"' % string.rstrip(line)

tail.tail('/var/log/all', callback).mainloop()
'''

import time
import string
import os

class tail:
def __init__(self, filename, callback, tailbytes = 0):
'''Create a new tail instance.
Create a tail object which periodicly polls the specified file looking
for new data which was written. The callback routine is called for each
new line found in the file.

@return Nothing
@param filename File to read.
@param callback Function which takes one argument, called with each
line read from the file.
@param tailbytes Specifies bytes from end of file to start reading
(defaults to 0, meaning skip entire file, -1 means read full file).
'''
self.skip = tailbytes
self.filename = filename
self.callback = callback
self.fp = None
self.lastSize = 0
self.lastInode = -1
self.data = ''

def process(self):
'''Examine file looking for new lines.
When called, this function will process all lines in the file being
tailed, detect the original file being renamed or reopened, etc...
This should be called periodicly to look for activity on the file.

@return Nothing
'''
# open file if it's not already open
if not self.fp:
try:
self.fp = open(self.filename, 'r')
stat = os.stat(self.filename)
self.lastIno = stat[1]
if self.skip >= 0 and stat[6] > self.skip:
self.fp.seek(0 - (self.skip), 2)
self.skip = -1
self.lastSize = 0
except:
if self.fp: self.fp.close()
self.skip = -1 # if the file doesn't exist, we don't skip
self.fp = None
if not self.fp: return

# check to see if file has moved under us
try:
stat = os.stat(self.filename)
thisSize = stat[6]
thisIno = stat[1]
if thisSize < self.lastSize or thisIno != self.lastIno:
raise Exception
except:
self.fp.close()
self.fp = None
self.data = ''
return

# read if size has changed
if self.lastSize < thisSize:
while 1:
thisData = self.fp.read(4096)
if len(thisData) < 1:
break
self.data = self.data + thisData

# process lines within the data
while 1:
pos = string.find(self.data, '\n')
if pos < 0: break
line = self.data[:pos]
self.data = self.data[pos + 1:]
# line is line read from file
if self.callback: self.callback(line)

self.lastSize = thisSize
self.lastIno = thisIno

def mainloop(self, sleepfor = 5):
'''Loop forever processing activity on the tail object.
This routine is intended to be called in programs which do not need
to do other processing. This routine never returns.

@return Never returns
@param sleepfor Seconds between processing (default is 5 seconds).
'''
while 1:
self.process()
time.sleep(sleepfor)

if __name__ == "__main__":
def callback(line):
print 'Line: "%s"' % string.rstrip(line)

tail('/var/log/all', callback).mainloop()
</pre>

[[Category:Python]]
[[Category:Tools]]

Tail.py - Revision history

PeterHarding at 06:09, 19 July 2009

PeterHarding: New page: =Script=
#!/usr/bin/python '''A module which implements a unix-like "tail" of a file. A callback is made for every new line found in the file. Options specify whether the existing...