From: Robert Klemme <shortcutter@...>
Date: 2007-08-24T21:01:49+09:00
Subject: Re: How to append some data at the beginning of a file

2007/8/24, Uday Thokala <udaykanth_t@yahoo.co.in>:
> Ronald Fischer wrote:
> >> I am newbie to Ruby so please spare me if the question looks silly. My
> >> question is how to append data at the beginning of a file?
> >
> > This is not so much a Ruby question, since nearly no operating system
> > directly
> > allows appending data to the beginning of a file.
>
> Thanks Ronald for your comments. I am wondering may be ruby got some way
> around it.
>
> > The general solution
> > is to create a new file, putting there the data in the right order,
> > delete
> > the old file and rename the new file to the name of the old one.
> >
> > Renaming a file is done like this:
> >
> >   File.rename("oldname","newname")
>
> Yeah I implemented the above mentioned solution and it's working fine.
> The code is
>
> 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();
> newfile.close();
>
> File.delete("test");
> File.rename("test1", "test");

Just a few remarks: better return to your old habit and use the block
form of File.open (btw, you do not need to close the file, File#open
takes care of that when the block is left - even in case of an
exception).

You don't need to terminate lines with ";".

Also, you can use variables to make your life easier:

file = "test"
tmp = file + "~"

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

  File.foreach file do |line|
    out.puts line
  end
end

File.delete file
File.rename tmp, file

Kind regards

robert