Linux – Fast extraction of a time range from syslog logfile

Update: I've replaced the original code with an updated version with numerous improvements. Let's call this (actual?)alpha-quality.

This version includes:

• command-line option handling
• command-line date format validation
• some try blocks
• line reading moved into a function

Original text:

Well what do you know? "Seek" and ye shall find! Here is a Python program that seeks around in the file and uses a more-or-less binary search. It's considerably faster than that AWK script that other guy wrote.

It's (pre?)alpha-quality. It should have try blocks and input validation and lots of testing and could no doubt be more Pythonic. But here it is for your amusement. Oh, and it's written for Python 2.6.

New code:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# timegrep.py by Dennis Williamson 20100113
# in response to http://serverfault.com/questions/101744/fast-extraction-of-a-time-range-from-syslog-logfile

# thanks to serverfault user http://serverfault.com/users/1545/mike
# for the inspiration

# Perform a binary search through a log file to find a range of times
# and print the corresponding lines

# tested with Python 2.6

# TODO: Make sure that it works if the seek falls in the middle of
#       the first or last line
# TODO: Make sure it's not blind to a line where the sync read falls
#       exactly at the beginning of the line being searched for and
#       then gets skipped by the second read
# TODO: accept arbitrary date

# done: add -l long and -s short options
# done: test time format

version = "0.01a"

import os, sys
from stat import *
from datetime import date, datetime
import re
from optparse import OptionParser

# Function to read lines from file and extract the date and time
def getdata():
    """Read a line from a file

    Return a tuple containing:
        the date/time in a format such as 'Jan 15 20:14:01'
        the line itself

    The last colon and seconds are optional and
    not handled specially

    """
    try:
        line = handle.readline(bufsize)
    except:
        print("File I/O Error")
        exit(1)
    if line == '':
        print("EOF reached")
        exit(1)
    if line[-1] == '\n':
        line = line.rstrip('\n')
    else:
        if len(line) >= bufsize:
            print("Line length exceeds buffer size")
        else:
            print("Missing newline")
        exit(1)
    words = line.split(' ')
    if len(words) >= 3:
        linedate = words[0] + " " + words[1] + " " + words[2]
    else:
        linedate = ''
    return (linedate, line)
# End function getdata()

# Set up option handling
parser = OptionParser(version = "%prog " + version)

parser.usage = "\n\t%prog [options] start-time end-time filename\n\n\
\twhere times are in the form hh:mm[:ss]"

parser.description = "Search a log file for a range of times occurring yesterday \
and/or today using the current time to intelligently select the start and end. \
A date may be specified instead. Seconds are optional in time arguments."

parser.add_option("-d", "--date", action = "store", dest = "date",
                default = "",
                help = "NOT YET IMPLEMENTED. Use the supplied date instead of today.")

parser.add_option("-l", "--long", action = "store_true", dest = "longout",
                default = False,
                help = "Span the longest possible time range.")

parser.add_option("-s", "--short", action = "store_true", dest = "shortout",
                default = False,
                help = "Span the shortest possible time range.")

parser.add_option("-D", "--debug", action = "store", dest = "debug",
                default = 0, type = "int",
                help = "Output debugging information.\t\t\t\t\tNone (default) = %default, Some = 1, More = 2")

(options, args) = parser.parse_args()

if not 0 <= options.debug <= 2:
    parser.error("debug level out of range")
else:
    debug = options.debug    # 1 = print some debug output, 2 = print a little more, 0 = none

if options.longout and options.shortout:
    parser.error("options -l and -s are mutually exclusive")

if options.date:
    parser.error("date option not yet implemented")

if len(args) != 3:
    parser.error("invalid number of arguments")

start = args[0]
end   = args[1]
file  = args[2]

# test for times to be properly formatted, allow hh:mm or hh:mm:ss
p = re.compile(r'(^[2][0-3]|[0-1][0-9]):[0-5][0-9](:[0-5][0-9])?$')

if not p.match(start) or not p.match(end):
    print("Invalid time specification")
    exit(1)

# Determine Time Range
yesterday = date.fromordinal(date.today().toordinal()-1).strftime("%b %d")
today     = datetime.now().strftime("%b %d")
now       = datetime.now().strftime("%R")

if start > now or start > end or options.longout or options.shortout:
    searchstart = yesterday
else:
    searchstart = today

if (end > start > now and not options.longout) or options.shortout:
    searchend = yesterday
else:
    searchend = today

searchstart = searchstart + " " + start
searchend = searchend + " " + end

try:
    handle = open(file,'r')
except:
    print("File Open Error")
    exit(1)

# Set some initial values
bufsize = 4096  # handle long lines, but put a limit them
rewind  =  100  # arbitrary, the optimal value is highly dependent on the structure of the file
limit   =   75  # arbitrary, allow for a VERY large file, but stop it if it runs away
count   =    0
size    =    os.stat(file)[ST_SIZE]
beginrange   = 0
midrange     = size / 2
oldmidrange  = midrange
endrange     = size
linedate     = ''

pos1 = pos2  = 0

if debug > 0: print("File: '{0}' Size: {1} Today: '{2}' Now: {3} Start: '{4}' End: '{5}'".format(file, size, today, now, searchstart, searchend))

# Seek using binary search
while pos1 != endrange and oldmidrange != 0 and linedate != searchstart:
    handle.seek(midrange)
    linedate, line = getdata()    # sync to line ending
    pos1 = handle.tell()
    if midrange > 0:             # if not BOF, discard first read
        if debug > 1: print("...partial: (len: {0}) '{1}'".format((len(line)), line))
        linedate, line = getdata()

    pos2 = handle.tell()
    count += 1
    if debug > 0: print("#{0} Beg: {1} Mid: {2} End: {3} P1: {4} P2: {5} Timestamp: '{6}'".format(count, beginrange, midrange, endrange, pos1, pos2, linedate))
    if  searchstart > linedate:
        beginrange = midrange
    else:
        endrange = midrange
    oldmidrange = midrange
    midrange = (beginrange + endrange) / 2
    if count > limit:
        print("ERROR: ITERATION LIMIT EXCEEDED")
        exit(1)

if debug > 0: print("...stopping: '{0}'".format(line))

# Rewind a bit to make sure we didn't miss any
seek = oldmidrange
while linedate >= searchstart and seek > 0:
    if seek < rewind:
        seek = 0
    else:
        seek = seek - rewind
    if debug > 0: print("...rewinding")
    handle.seek(seek)

    linedate, line = getdata()    # sync to line ending
    if debug > 1: print("...junk: '{0}'".format(line))

    linedate, line = getdata()
    if debug > 0: print("...comparing: '{0}'".format(linedate))

# Scan forward
while linedate < searchstart:
    if debug > 0: print("...skipping: '{0}'".format(linedate))
    linedate, line = getdata()

if debug > 0: print("...found: '{0}'".format(line))

if debug > 0: print("Beg: {0} Mid: {1} End: {2} P1: {3} P2: {4} Timestamp: '{5}'".format(beginrange, midrange, endrange, pos1, pos2, linedate))

# Now that the preliminaries are out of the way, we just loop,
#     reading lines and printing them until they are
#     beyond the end of the range we want

while linedate <= searchend:
    print line
    linedate, line = getdata()

if debug > 0: print("Start: '{0}' End: '{1}'".format(searchstart, searchend))
handle.close()