[Tutor] What am I missing?

[Brian van den Broek]

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