From: Robert Klemme <shortcutter@...>
Date: 2009-12-13T23:35:06+09:00
Subject: Re: Question about file management [read]

On 13.12.2009 14:37, Panagiotis Atmatzidis wrote:

> On 13 2009, at 1:20, Robert Klemme wrote:
> 
>> On 12.12.2009 21:05, Panagiotis Atmatzidis wrote:
>>> A salut to the list,
>>>
>>> I need read info from a file, extract the info that I want which is the date and IP and dump them into a database (mysql).
>>>
>>> However, this file gets constantly updated, sits on /var/log/.
>>>
>>> Until now I have used just the file.open and file.read methods. However, I feel that both ways are not suitable for what I want to do, because I will need to make a selection between old and new entries every time my script reads the file to extract info.
>>>
>>> What is the *standard* (or best) way to manage this situation?
>>>
>>> Here is the class which reads the file:
>>>
>>> class ReadIPs
>>>   def self.ip(log)
>>>     file = File.open(log)
>> Ha!  There you are not using block form of File.open and you do not have the #close in ensure! :-)
> 
> I don't understand what do you mean by 'ensure'.

There full syntax you can have with begin end blocks is

begin
rescue
else
ensure
end

See also
http://blog.rubybestpractices.com/posts/rklemme/002_Writing_Block_Methods.html
http://blog.rubybestpractices.com/posts/rklemme/001-Using_blocks_for_Robustness.html

>>>     file.each_line do |line|
>>>       if line.include?("Ban")
>>>          a = line.split(" ")
>>>          date = a[0]
>>>          ip = a[6]
>>>          puts "date: #{date} IP: #{ip}"
>>>       end
>>>     end
>>>     file.close
>>>   end
>>> end
>>>
>>> I use File.open now but I should use something like File.append or similar? Note that I will never write to this file, it's just the file that contains the info. Every time a new line appears that contains the word "Ban" I want to trigger this...
>>>
>>> Best regards
>> I can't test it right now but this might be an option.
>>
>> File.open log do |io|
>>  loop do
>>    io.each do |line|
>>      # whatever...
>>    end
>>
>>    # v2: pos = io.tell
>>    sleep 10 # whatever interval is appropriate
>>    # v1: io.seek(0, IO::SEEK_SET)
>>    # v2: io.seek(pos, IO::SEEK_CUR)
>>  end
>> end
>>
>> Maybe you have to do one of the variants to clear eof flag:
>>
>> v1: seek to offset 0 of current position
>> v2: fetch the position before the sleep and then seek to that absolute position

> Oh, this solutions, might work but I think that it's a bit overcomplicated for me. I did not used IO and "seek" yet...

#seek is not used in the simplest case.  What about reading up on #seek 
and #tell or trying out the code?  I don't see where this is 
complicated.  If that's too complicated for you then I either my 
explanation made it look more complicated that it actually is or you 
should abandon software development.  You'll encounter far more 
complicated things in the course of it.

> I found online [1] a few examples but I did not had the time to test them.
> 
> Maybe something like: 
> 
> file   = File.open(path, File::WRONLY|File::APPEND)
> 
> Will do.

Will do what?

> [1] http://pleac.sourceforge.net/pleac_ruby/fileaccess.html

I am not sure whether pleac is a proper source to enter the world of 
ruby.  AFAIK their aim is to compare languages - not to present an 
introductory read of particular languages.  There are quite a few 
tutorials and books out there for Ruby.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/