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From: Xavier Noria on 22 Jul 2010 10:33
Check the elif gem, by James Edward Gray II.

It is a port of File::ReadBackwards, whose documentation explains the approach:

http://search.cpan.org/~uri/File-ReadBackwards-1.04/ReadBackwards.pm#DESIGN

-- fxn

From: Urabe Shyouhei on 22 Jul 2010 11:36
(2010/07/22 23:33), Xavier Noria wrote:
> Check the elif gem, by James Edward Gray II.
>
> It is a port of File::ReadBackwards, whose documentation explains the approach:
>
> http://search.cpan.org/~uri/File-ReadBackwards-1.04/ReadBackwards.pm#DESIGN

And says nothing about multiligualization because M17N cannot be achieved by
the approach, theoretically.

Maybe that's OK for Ted. I'm living in a different world than you perhaps.

From: James Edward Gray II on 22 Jul 2010 11:42
On Jul 22, 2010, at 10:36 AM, Urabe Shyouhei wrote:

> (2010/07/22 23:33), Xavier Noria wrote:
>> Check the elif gem, by James Edward Gray II.
>>
>> It is a port of File::ReadBackwards, whose documentation explains the approach:
>>
>> http://search.cpan.org/~uri/File-ReadBackwards-1.04/ReadBackwards.pm#DESIGN
>
> And says nothing about multiligualization because M17N cannot be achieved by the approach, theoretically.

Yes, I wrote it before Ruby 1.9's m17n engine. I only use it on ASCII logs, where it works fine. I would not recommend it for encoded data.

James Edward Gray II
From: Xavier Noria on 22 Jul 2010 12:04
On Thu, Jul 22, 2010 at 5:36 PM, Urabe Shyouhei <shyouhei(a)ruby-lang.org> wrote:

> And says nothing about multiligualization because M17N cannot be achieved by
> the approach, theoretically.

So in general you can't detect character boundaries going backwards?
You can always have cut characters and still have a valid buffer?

From: Robert Klemme on 22 Jul 2010 14:04
On 22.07.2010 16:22, Urabe Shyouhei wrote:
> (2010/07/22 22:06), Robert Klemme wrote:
>>> Then how about:
>>>
>>> File.open(f).each_line.inject(nil){|x,y|y}
>>>
>>> Slower than my first answer though.

>> A solution that is efficient for large files will
>> use File#seek to move position to the end of the file and go backwards
>> from there.
>
> No, that can't work -- or that works only when you are sticking on the ASCII
> character set. Multibyte encodings are not safe to read backwards
> (sometimes). The only safe way is to read the whole content from the
> beginning, at least one time.

Good point. Although pragmatically for fixed width and UTF-8 encoded
files it will work and the performance gains for large files are
significant enough to warrant this approach.

Cheers

robert


--
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