[Fwd: Re: [Tutor] What am I missing?]

[Brian van den Broek]

Tom,

glad you felt helped!

It's a bit past my bed-time, so I've fwd'ed your reply to the tutor list 
-- if you send your replies there, you have a much better chance of 
getting help. (I'm pretty new at programming, too.)

But a couple of things:

Are you sure you need regular expressions for your task? I'm not very 
familiar with the re module, so my response didn't consider if you were 
using it correctly. But for simple searches, you can use string methods. 
(Also, rather than import string in the code below, you should use the 
string methods -- the string module, as I understand it, is still there 
for backwards compatibility, but it is not the preferred technique.)

Best,

Brian vdB


-------- Original Message --------
Subject: Re: [Tutor] What am I missing?
Date: Mon, 27 Sep 2004 01:03:40 -0400
From: Tom Tucker <tktucker at gmail.com>
Reply-To: Tom Tucker <tktucker at gmail.com>
To: Brian van den Broek <bvande at po-box.mcgill.ca>
References: <2a278ffe040926205866e40963 at mail.gmail.com> 
<415797EE.1010401 at po-box.mcgill.ca>

Brain,
Thanks for the help.  I APPRECIATE IT!
  I think, I understand.  I have to zero out or empty the "found"
variable.  Below is the /var/log/messages log, the Python script, and
the script output when executed.

If you notice, my search criteria is based on the word 'CROND', my log
(/var/log/messages) does NOT contain that word.  WIth that being said,
when the script is excuted, technically nothing should be printed to
STDOUT.  Correct?


/var/log/messages
###########
root at loki ttucker/Python/isalog # cat /var/log/messages
Sep 27 00:49:46 loki syslogd 1.4.1: restart.
Sep 27 00:49:46 loki kernel: klogd 1.4.1, log source = /proc/kmsg started.
Sep 27 00:49:46 loki kernel: Inspecting 
/boot/System.map-2.6.3-7mdk-i686-up-4GB
Sep 27 00:49:46 loki kernel: Loaded 29391 symbols from
/boot/System.map-2.6.3-7mdk-i686-up-4GB.
Sep 27 00:49:46 loki kernel: Symbols match kernel version 2.6.3.
Sep 27 00:49:46 loki kernel: No module symbols loaded - kernel modules
not enabled.
Sep 27 00:50:03 loki su(pam_unix)[21569]: session opened for user root
by (uid=0)
root at loki ttucker/Python/isalog #

Test Script (HAS CHANGED)
########
import os, re, string

findme = re.compile('CROND')
logfile = os.system('tail -f /var/log/messages')
for line in logfile:
         found = re.search(findme, line)
         if found:
                 print line,
                 found = ''
         else:
                 print "not found"
                 found = ''

SCRIPT OUTPUT
###############
root at loki ttucker/Python/isalog # ./newv5.py
Sep 27 00:49:46 loki syslogd 1.4.1: restart.
Sep 27 00:49:46 loki kernel: klogd 1.4.1, log source = /proc/kmsg started.
Sep 27 00:49:46 loki kernel: Inspecting 
/boot/System.map-2.6.3-7mdk-i686-up-4GB
Sep 27 00:49:46 loki kernel: Loaded 29391 symbols from
/boot/System.map-2.6.3-7mdk-i686-up-4GB.
Sep 27 00:49:46 loki kernel: Symbols match kernel version 2.6.3.
Sep 27 00:49:46 loki kernel: No module symbols loaded - kernel modules
not enabled.
Sep 27 00:50:03 loki su(pam_unix)[21569]: session opened for user root
by (uid=0)




On Mon, 27 Sep 2004 00:32:46 -0400, Brian van den Broek
<bvande at po-box.mcgill.ca> wrote:
> Tom Tucker said unto the world upon 2004-09-26 23:58:
> 
> 
> > Good evening! Any thoughts on this one?
> >
> > The goal is to 'tail -f /var/log/messages' and if the line contains
> > "CROND" for example, then print that line.  The below script does a
> > great job of tailing and printing, but it prints EVERYTHING.
> >
> > ##################
> > #!/usr/bin/python
> >
> > import os, re
> >
> > findme = re.compile('CROND')
> > logfile = os.system('tail -f /var/log/messages')
> > for line in logfile:
> >         found = re.search(findme, line)
> >         if found:
> >                 print line,
> >         else:
> >                 print "not found"
> > ####################
> >
> >
> > Thanks,
> >
> > Tom
> 
> Hi Tom,
> 
> with the line:
> 
>  >         found = re.search(findme, line)
> 
> you assign found a value which evaluates as True.
> 
> Then, for each subsequent line through the for loop you are testing if
> found evaluates as True. And it does, because you made it so. ;-)
> 
> One fix would be to say this instead:
> 
>         if found:
>                 print line,
>                 found = ''  # or [], (), None, etc. Anything that
>                             # evaluates as False will do.
> 
> Then, next time through, your if test will fail (unless of course your
> re.search matched again).
> 
> I'm not sure of your intent; if you want "not found" to be printed only
> when you had no matches, you will need to add a bit more.
> 
> HTH,
> 
> Brian vdB
>