From: Bill Kelly <billk@...>
Date: 2009-11-28T09:26:36+09:00
Subject: Re: Ruby byte access to disk sectors like dd does


From: "Robert Klemme" <shortcutter@googlemail.com>
>
> 2009/11/27 Bill Kelly <billk@cts.com>:
>>
>> ruby -e 'File.open("/dev/hdb", "rb") {|io| print(io.read(512))}' | hexdump -C
> 
> Just a small remark: when using #read for reading I would prefer to
> also use #write for writing.  It is more symmetric and It may actually
> be that #print does a bit more in light of i18n support in Ruby 1.9.
> So that would be
> 
> ruby -e 'File.open("/dev/hdb", "rb") {|io|
> $stdout.write(io.read(512))}' | hexdump -C

Hmm.  From my point of view, symmetry-for-symmetry's sake can't
generally apply here, because, for example, I would expect the
following to be bad form:

  $stdout.syswrite(io.sysread(512))}' | hexdump -C

I.e., since 'io' and stdout are separate streams, I may choose
to call *only* 'sys' methods on 'io', but I can't in turn 
reasonably expect to call corresponding 'sys' methods on the
(presumably buffered) $stdout ...

However, your observation did make me curious as to how different
'print' might be from 'write' vis-a-vis m17n on ruby 1.9.x.

In the 1.9.2dev sources, it appears 'write' and 'print' are
nearly identical (rb_io_print calls rb_io_write), but, that
each argument to print will be followed by the "output record
separator" string, if it is non-nil.   ( $\ )

So if we wish to avoid the possibility of $\ contaminating our
output, we indeed should call write instead of print.


> The more fun solution would of course be to code the hex dumping in
> Ruby also. :-)

:)  Here's a stab at it... (it does work properly if the last
read returns fewer than 16 bytes.)

ruby -e 'File.open("/dev/hdb", "rb") {|io| print(io.read(512))}' |
 ruby -e 'i=0; while(x=ARGF.read(16)); puts("%08x %-32s %s" % [i, x.unpack("H*"), x.tr("^\040-\176",".")]); i+=16; end'


Regards,

Bill