From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-07-18T22:00:39+09:00
Subject: Re: Reading total lines of file then displaying in reverse?

On Mon, 18 Jul 2005, Tristan Knowles wrote:

> How would I use File or IO to read all the lines of a
> file, then display the contents in reverse?
>
> Its for a simple log reading script, which I would
> like to have read the total lines, then display with
> the latest entries first, and show x amount of log
> entries per page.
>
> I'm currently just dumping the whole, or part of the
> log with:
>
> ======
> IO.readlines("my.log")[1..49].each_with_index do
> |line, index|
> ======
>
> I guess I would have to count all lines, then assign a
> variable to the last number it counts, and then work
> in reverse from this variable...  hmmm.  I'm not
> sure:P
>
> Any ideas?

if i understand you correctly:

   harp:~ > cat a.txt
   42
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10


   harp:~ > cat a.rb

   lines = IO::readlines(ARGV.shift)

   page_separator = '=' * 79
   page_size = 5
   length = $.
   n_pages = (length / page_size) + 1

   catch('done') do
     n_pages.times do
       page_size.times do
         throw 'done' if lines.empty?
         print lines.pop
       end
       puts page_separator
     end
   end



   harp:~ > ruby a.rb a.txt
   10
   9
   8
   7
   6
   ===============================================================================
   5
   4
   3
   2
   1
   ===============================================================================
   42


'$.' is always the number of lines read after an IO::readlines.

hth.


-a
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