From: Robert Klemme <shortcutter@...>
Date: 2009-11-29T21:10:11+09:00
Subject: Re: Ruby byte access to disk sectors like dd does

On 29.11.2009 01:25, Gary Hasson wrote:
> Thank you all for your guidance. I am now able to do with Ruby what I 
> previously need dd for.
> 
> However, I am not able to cleanly test for the end of file due to the 
> following error:
> 
> until file_1.eof?
>   file_1_byte = file_1.sysread( 1 )
> end
> 
> ERROR MSG:
> /Ruby_file_test.rb:23:in `sysread': sysread for buffered IO (IOError)
>   from ./Ruby_file_test.rb:23
> 
> All of my file accesses are sysread, syswrite, and sysseek, which are 
> not compatible with IO#eof.
> 
> Using the file size to prevent hitting the EOF does not work for 
> /dev/sdb.
> 
> So, I just let it generate an EOF error and then rescue it.
> 
> It seems like there ought to be a working EOF function for IO#sys...

Question is why do you use #sysread in the first place?  As far as I can 
see there is no advantage of using #sysread here.

Also, reading a single byte at a time might be easier for the 
implementation but it is almost inevitably dramatically slower than 
reading in chunks.  *If* you use #sysread you should definitively read 
in chunks because #sysread does not buffer IIRC.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/