From: Andy <agunnerson@...>
Date: 2008-02-18T13:38:11+09:00
Subject: Re: Help with Writing Replacement Text to Files

Thomas,

I'm new to Ruby (only a few days) but this is something I think I can
actually help you with.  I had to do some searching and I came across
this website ..
http://pleac.sourceforge.net/pleac_ruby/fileaccess.html

Search for 'Modifying a File in Place Without a Temporary File' and
you'll find the code.  I'll paste it here though just to make it quick
and easy ..

File.open('itest', 'r+') do |f|   # open file for update
    lines = f.readlines           # read into array of lines
    lines.each do |it|            # modify lines
        it.gsub!(/foo/, 'QQQ')
    end
    f.pos = 0                     # back to start
    f.print lines                 # write out modified lines
    f.truncate(f.pos)             # truncate to new length
end                               # file is automatically closed

r+ is the mode that allows you to read and write to the file.  I made
a text file named itest with this for content ..

foo foo
bar bar
foo foo

I ran that code and the file got changed to ..

QQQ QQQ
bar bar
QQQ QQQ

That's what you're looking for isn't it?  I would suggest making a
backup of the files just in case there is a problem.  If that isn't
what you were looking for I apologize, reply back to this and I'll try
again haha.

-- 
-Andy
"I have a great faith in fools; self-confidence my friends call it." –
Edgar Allen Poe

On Feb 17, 2008 9:00 PM, Thomas Pierce <ruby@upgradeyourmind.com> wrote:
> Hello!
>
> I'm new to ruby and been reading this very active list for about a
> couple of week.
>
> I have a project at work where I need to write a simple script to
> scrub IP addresses from configuration files for classified networks we
> work in sometimes. The goal is to cleanse configuration files
> sometimes required for support of any specific network addressing
> information. Here is what I've come up with so far. While this works
> in IRB on the file object I create, I cannot figure out how to write
> the changes back in place to the actual file itself back on the regex
> I'm using:
>
>   config_file = File.open("config.txt")
>          config_txt = config_file.read
>          config_txt.gsub!(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/,
> "000.000.000.000")
>
> I do understand that the default action here is read-only. How to do I
> parse with the regex on the current file and replace matching strings
> without either appending to the file, overwriting the file, or
> creating a new file?
>
> Thanks!
>
> ~Thomas
>
>