Re: Editing a text file and then replacing existing file

On 2/2/2011 9:53 AM, Bob Hatch wrote:
> I have a script that I use to find text in a file and then delete the
> line(s) the text is on. That part works. What I have been unsuccessfully
> trying to do is take the new text and overwrite the existing file that I
> did the search and delete on. Here is my existing code that finds the
> lines and deletes them:
> 
> path='c:\ruby192\my_projects\IIS_Logs\ex11012607.log'
> search_text = %r{/memberinfo/downline/tree/can.asp}
> search_text2 = %r{/memberinfo/downline/tree/disto.asp}
> search_text3 = %r{/styles/default.css}
> search_text4 = %r{/scripts/generalscript.js}
> search_text5 = %r{/memberinfo/downline/tree/upl.asp}
> search_text6 = %r{/scripts/wz_jsgraphics.js}
> search_text7 = %r{/memberinfo/downline/tree/disfo2.asp}
> search_text8 = %r{/styles/png.htc}
> File.open(path, 'a+') do |file|
>   file.each_line do |line|
>       puts(line) unless line =~ search_text ||
>   puts(line) unless line =~ search_text2 ||
>       puts(line) unless line =~ search_text3 ||
>       puts(line) unless line =~ search_text4 ||
>       puts(line) unless line =~ search_text5 ||
>       puts(line) unless line =~ search_text6 ||
>       puts(line) unless line =~ search_text7 ||
>       puts(line) unless line =~ search_text8
>    end
> file.write(line)
> file.close
> end

First of all, let's simplify this code by using a single regexp that
will match all lines of interest.  This uses the x option for the regexp
construction so that the format is a little more legible:

search_text = %r{
  /memberinfo/downline/tree/can.asp    |
  /memberinfo/downline/tree/disto.asp  |
  /styles/default.css                  |
  /scripts/generalscript.js            |
  /memberinfo/downline/tree/upl.asp    |
  /scripts/wz_jsgraphics.js            |
  /memberinfo/downline/tree/disfo2.asp |
  /styles/png.htc
}x

Beware that the x option will cause any unescaped whitespace in your
regexp to be ignored, so you need to take care if you need to match a
file path that has spaces in it.

With this regexp you would be able to use a single puts(line) call.
BTW, you should really try to avoid duplicated code like you have with
your puts lines in general.  Alarm bells should go off in your head if
you see that sort of thing.  More importantly though, you need to take a
closer look at what you're doing there with the || operator.  That's not
exactly doing what you seem to intend. ;-)

Now we get to the meat of your problem.  You can't write to the file
from which you're reading without manually maintaining at least 2
pointers into the file, one for your current read position and another
for your write position.  It's *much* easier actually create a new file
to hold the filtered data and then use that file to replace the original:

File.open(source_path) do |infile|
  File.open(temp_path, "w") do |outfile|
    infile.each_line do |line|
      outfile.write(line) unless line =~ search_text
    end
  end
end
File.rename(temp_path, source_path)

-Jeremy