From: Simon Strandgaard <neoneye@...>
Date: 2004-05-20T20:33:44+09:00
Subject: Re: seraching backward in files

Patrick Gundlach wrote:
> I'd wonder if there is a simple method in searching backward in
> files. I want to read a pdf file, so I have to do the following:
> 
> 1) goto the end of file (pdffile.seek(0,IO::SEEK_END))
> 2) search backward for the string "%%EOF" within the last 1024 bytes
> 3) search backward for "startxref"
> 4) read the next bytes,.....
> 
> 
> Do I have to write my own seach backward routine or is there some
> functionality for it?

Ruby's native regexp engine cannot go backwards... thats why I
am working on my own regexp-engine. However I don't have a 
FileInputStream class yet (but I can easily add one).

The text is spelled backwards, because we want to search backwards.

# pseudo code
iterator = file.create_iterator_end.reverse
re = NewRegexp.new('(?xm) .{0,1024} FOE%% .{0,4000} ferxtrats')
matchdata = re.match(iterator)

The engine is written entirely in Ruby, so speed isn't impressive.
Its fairly compatible with Ruby1.8's builtin GNU regexp, and its
carefully tested (more than 2000 tests).
http://raa.ruby-lang.org/list.rhtml?name=regexp

-- 
Simon Strandgaard