From: Robert Klemme <shortcutter@...>
Date: 2007-06-18T15:55:01+09:00
Subject: Re: healp reading / writing binary strings.

On 18.06.2007 03:52, Melissa Silas wrote:
> Hey, I'm looking for some help with reading / writing binary string.
> Just need some help understanding what exactly is going on..
> 
> if I have a string like:
> str = "\t\005\001\006\afoo\006\abar"
> 
> Or if I have something like:
> str =
> "\t\025\001\004\001\004\002\004\003\004\004\004\005\004\006\004\a\004\b\004\t\004\n"
> 
> What exactly kind of format is that?

Um, how can we know what format this is?  I mean, you came up with that 
string.  The definition above just uses octal escapes.  You can as well 
have hex codes:

irb(main):013:0> "\x21\x20\x40"
=> "! @"

 > How do I parse it / read binary
> data from it?

Depends on what you want to do with it.  If you want to access bytes you 
can simply do this

irb(main):014:0> s = "\t\001"
=> "\t\001"
irb(main):015:0> s[0]
=> 9
irb(main):016:0> s[1]
=> 1

If you want bits you can do

irb(main):017:0> s.unpack "b*"
=> ["1001000010000000"]
irb(main):018:0> s.unpack "b8b8"
=> ["10010000", "10000000"]
irb(main):019:0> s.unpack "b4*"
=> ["1001"]
irb(main):020:0> s.unpack "b4b4b4b4"
=> ["1001", "1000", "", ""]
irb(main):021:0> s.unpack "b4b4b"
=> ["1001", "1000", ""]
irb(main):022:0> s.unpack "b4b4"
=> ["1001", "1000"]

Please see #unpack docs for more info.

 > And how can I write the same type of string from say an
> array? ["foo","bar"]?

"Write from an array"?  I don't understand what you mean. If you want to 
put it into an array, you can simply do

irb(main):023:0> ["foo", "\tbar\n"]
=> ["foo", "\tbar\n"]

Kind regards

	robert