From: Ghislain Mary <nospam@...>
Date: 2005-04-19T18:32:23+09:00
Subject: Re: Modifying content in a file

Robert Klemme a 辿crit :
> You can do that easier:
> 
> to_file.puts( /^caption:/ =~ line ? caption : line )
> 

In fact, I am doing several substitution, but I forgot to tell it.

> 
> Depends on your file's sizes.  If they are moderately sized you can slurp
> the whole thing in, modify contents in mem with a single gsub and then
> write them in one go.
> 

Thanks. Since the file can be quite large, I continue using something
like before but with a Tempfile now. That gives something like:

require 'tempfile'
require 'fileutils'
include FileUtils

def clean_file(filename)
   # Define the new caption
   caption = "caption: my caption"

   # Process the content of the file
   begin
     tf = Tempfile.new(filename)
     File.open(filename) do |from_file|
       from_file.each do |line|
         case
           when line =~ /^caption:/: line.sub!($&, caption)
           # Other substitutions...
         end
         tf.print line
       end
     end
   ensure
     tf.close unless tf.nil?
   end

   # Replace the previous file with the new.
   cp(tf.path, filename)
end


But can't we open a file in read-write mode and directly do
substitutions in it without using an auxiliary file?

Ghislain