From: Melissa Silas <beingthexemplarylists@...>
Date: 2007-06-19T00:17:38+09:00
Subject: Re: healp reading / writing binary strings.

Robert Klemme wrote:
> On 18.06.2007 03:52, Melissa Silas wrote:
>> 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


Thanks that helps.. Couple more questions..

for this example:
s = "\t\001"
puts s[0] -> 9
How does \t come out as 9? Is that the tab char which in turn is the 
number 9 in ascii table?

for this example:
s = "\001"
Ok so now I know this is octal, does the octal value I supply correspond 
to the ascii table as well?

for this example:
s = "\x01"
for hex, does the hex value I supply correspond to the ascii table as 
well?

Thanks for the help. This is helping me understand this a bunch..

-Melissa

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