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pygtail.py
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#!/usr/bin/python -tt
# -*- coding: utf-8 -*-
# pygtail - a python "port" of logtail2
# Copyright (C) 2011 Brad Greenlee <[email protected]>
#
# Derived from logcheck <http://logcheck.org>
# Copyright (C) 2003 Jonathan Middleton <[email protected]>
# Copyright (C) 2001 Paul Slootman <[email protected]>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
from os import stat
from os.path import exists
import sys
import glob
import string
from optparse import OptionParser
__version__ = '0.2'
class Pygtail(object):
"""
Creates an iterable object that returns only unread lines.
"""
def __init__(self, filename, offset_file=None, paranoid=False):
self.filename = filename
self.paranoid = paranoid
self._offset_file = offset_file or "%s.offset" % self.filename
self._offset_file_inode = 0
self._offset = 0
self._fh = None
self._rotated_logfile = None
# if offset file exists, open and parse it
if exists(self._offset_file):
offset_fh = open(self._offset_file, "r")
(self._offset_file_inode, self._offset) = \
[string.atoi(line.strip()) for line in offset_fh]
offset_fh.close()
if self._offset_file_inode != stat(self.filename).st_ino:
# The inode has changed, so the file might have been rotated.
# Look for the rotated file and process that if we find it.
self._rotated_logfile = self._determine_rotated_logfile()
def __iter__(self):
return self
def next(self):
"""
Return the next line in the file, updating the offset.
"""
try:
line = self._filehandle().next()
except StopIteration:
# we've reached the end of the file; if we're processing the
# rotated log file, we can continue with the actual file; otherwise
# update the offset file
if self._rotated_logfile:
self._rotated_logfile = None
self._fh.close()
self._offset = 0
# open up current logfile and continue
try:
line = self._filehandle().next()
except StopIteration: # oops, empty file
self._update_offset_file()
raise
else:
self._update_offset_file()
raise
if self.paranoid:
self._update_offset_file()
return line
def readlines(self):
"""
Read in all unread lines and return them as a list.
"""
return [line for line in self]
def read(self):
"""
Read in all unread lines and return them as a single string.
"""
lines = self.readlines()
if lines:
return ''.join(lines)
else:
return None
def _filehandle(self):
"""
Return a filehandle to the file being tailed, with the position set
to the current offset.
"""
if not self._fh or self._fh.closed:
filename = self._rotated_logfile or self.filename
self._fh = open(filename, "r")
self._fh.seek(self._offset)
return self._fh
def _update_offset_file(self):
"""
Update the offset file with the current inode and offset.
"""
offset = self._filehandle().tell()
inode = stat(self.filename).st_ino
fh = open(self._offset_file, "w")
fh.write("%s\n%s\n" % (inode, offset))
fh.close()
def _determine_rotated_logfile(self):
"""
We suspect the logfile has been rotated, so try to guess what the
rotated filename is, and return it.
"""
rotated_filename = self._check_rotated_filename_candidates()
if (rotated_filename and exists(rotated_filename) and
stat(rotated_filename).st_ino == self._offset_file_inode):
return rotated_filename
else:
return None
def _check_rotated_filename_candidates(self):
"""
Check for various rotated logfile filename patterns and return the first
match we find.
"""
# savelog(8)
candidate = "%s.0" % self.filename
if (exists(candidate) and exists("%s.1.gz" % self.filename) and
(stat(candidate).st_mtime > stat("%s.1.gz" % self.filename).st_mtime)):
return candidate
# logrotate(8)
candidate = "%s.1" % self.filename
if exists(candidate):
return candidate
# dateext rotation scheme
candidates = glob.glob("%s-[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]" % self.filename)
if candidates:
candidates.sort()
return candidates[-1] # return most recent
# no match
return None
def main():
# command-line parsing
cmdline = OptionParser(usage="usage: %prog [options] logfile",
description="Print log file lines that have not been read.")
cmdline.add_option("--offset-file", "-o", action="store",
help="File to which offset data is written (default: <logfile>.offset).")
cmdline.add_option("--paranoid", "-p", action="store_true",
help="Update the offset file every time we read a line (as opposed to"
" only when we reach the end of the file).")
options, args = cmdline.parse_args()
if (len(args) != 1):
cmdline.error("Please provide a logfile to read.")
pygtail = Pygtail(args[0],
offset_file=options.offset_file,
paranoid=options.paranoid)
for line in pygtail:
sys.stdout.write(line)
if __name__ == "__main__":
main()