From: Rob Biedenharn <Rob@...>
Date: 2008-06-26T11:38:57+09:00
Subject: Re: how to write in the middle of a file

On Jun 25, 2008, at 8:59 PM, Roger Pack wrote:

> Greetings all.  For some reason the answer to this stumps me.
> Say I have an existing file, 1K long, and I want to write something
> right in the middle of it, without changing the file size.

meaning you want to OVERWRITE something in the middle, yes?

>
> I would have thought that
> a = File.open 'file', 'a+'
> a.seek 500
> a.write 'abc'
> a.close
>
> would work but doesn't seem to.  Thoughts?
> -R

Try a mode of 'r+'.  The 'a' part says you want all the writes to go  
the the end-of-file (whatever that happens to be at the time).

File.open 'file', 'w' do |f| f.write 'x'*1024 end

a = File.open 'file', 'r+'
a.seek 500
a.write 'abc'
a.close

all = File.read('file')

irb> puts all.size
1024
=> nil
irb> puts all.index('abc')
500
=> nil

You can puts(all) yourself if you want ;-)

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com