From: Jano Svitok <jan.svitok@...>
Date: 2007-08-24T20:55:01+09:00
Subject: Re: How to append some data at the beginning of a file

On 8/24/07, Ronald Fischer <ronald.fischer@venyon.com> wrote:
> > Thanks Ronald for your comments. I am wondering may be ruby
> > got some way
> > around it.
>
> It could, but I think it just happens too rare that someone
> wants to do this. In more than 2 decades of programming, I
> had this need only two or three times, for example.
>
> > newfile = File.new("test1","w")
> > newfile.puts "This line should appear at the top of each file";
> >
> > oldfile = File.open("test", "r+")
> > oldfile.each_line { |line| newfile.puts line}
> > oldfile.close();
>
> or simply
>
>   newfile.puts(File.read("test"))
>
> so you don't need the Ruby variable 'oldfile'.
>
> > newfile.close();
> >
> > File.delete("test");
> > File.rename("test1", "test");

1. it's better to use block form of File.open:

File.open("test1","w") do |newfile|
   newfile.puts "This line should appear at the top of each file"

   File.open("test", "r+") do |oldfile|
        oldfile.each_line { |line| newfile.puts line}
   end
end

File.delete("test");
File.rename("test1", "test");

The difference is that in case of an exception the file is closed
automatically. Otherwise you have to wait for garbage collector. It's
a good habit to get used to this style.

2. newfile.puts(File.read("test")) will read the entire file into
memory. Don't do this on large files - use the original way (or even
better, loop over the file with File#read(size)). For small files,
this read() is better.

3. newfile.puts(File.read("test")) will put an extra newline at the
end. Use either
 newfile << File.read("test")
or
 newfile.write(File.read("test"))