From: Vidar Hokstad <vidar@...>
Date: 2006-10-11T23:40:07+09:00
Subject: Re: scanning strings, backward?


Bil Kleb wrote:
> Vidar Hokstad wrote:
> > Bil Kleb wrote:
> >>   1) Goto line 1707 of the file
> >>   2) Search backward until line.match /\Wdt\W/i
> >>   3) Remove /dt/i
> >
> > For 2) Any particular reason why you need to search backwards? My
> > suggestion would be to look at String#gsub - that will help you handle
> > both 2) and 3) in one go.
>
> The problem is I only want to replace only
> the first occurrence before line 1707.

If you use IO#readlines you're working on an array of lines one by one.
So you'd do something
like this:

data = IO::readlines("test.txt")

data_to_replace.each do |r|
  (0..(r[:lineno]-1)).times { |i| data[lineno].gsub!(r[:pattern],"") }
end

Assuming "data_to_replace" contains an array of arrays each containing
:lineno => line number to stop at, and :pattern contains the pattern to
delete. If the pattern can occur multiple times per line you need to do
slightly more work, but gsub!() can take a block so you have full
control over what you do with the matches.

Vidar