From: mike@... (Mike Stok)
Date: 2004-01-28T01:59:55+09:00
Subject: Re: checksum with ruby, how?

In article <40168bd4$0$322$ba620e4c@news.skynet.be>,
shasckaw  <shasckaw@skynet.be> wrote:
>Hello there, I need help.
>I'm searching for checksum funtionality to use with ruby,
>it seems that I have all I need with digest/md5 but I can't find any 
>documentation about how to use it (searched on ruby-doc and RAA)
>
>Can someone help me?

To set a baseline, I used md5sum to checksum "hello there\n"

[mike@won mike]$ echo "hello there" > test.txt
[mike@won mike]$ md5sum test.txt
2d01d5d9c24034d54fe4fba0ede5182d  test.txt

I used irb and some guesswork to figure out its methods, the guess being
that Digest::MD5 was the right package:

[mike@ratdog mike]$ irb
>> require 'digest/md5'
=> true
>> d = Digest::MD5.new
=> d41d8cd98f00b204e9800998ecf8427e
>> d.methods - Object.methods
=> ["<<", "digest", "hexdigest", "update"]

So now I see what I can do, let's try updating the empty digest, pick
one of update or << ...

>> d << "hello there\n"
=> 2d01d5d9c24034d54fe4fba0ede5182d

Looks familiar :-)

>> hex = d.hexdigest
=> "2d01d5d9c24034d54fe4fba0ede5182d"

So you can use ruby's reflection to get a crude handle on things, but
documentation would say whether you can add content in the constructor:

>> d2 = Digest::MD5.new("hello there\n")
=> 2d01d5d9c24034d54fe4fba0ede5182d

It seems that you can initialise it with any String, so

>> File.open('/etc/passwd') do |f|
?>    puts Digest::MD5.new(f.read).hexdigest
>> end
f087dea38c54a8b40d3dbc8b0becfb4c
=> nil

or 

>> d3 = Digest::MD5.new
=> d41d8cd98f00b204e9800998ecf8427e
>> File.new('/etc/passwd').each_line { |l| d3 << l }
=> #<File:/etc/passwd>
>> d3.hexdigest
=> "f087dea38c54a8b40d3dbc8b0becfb4c"

are reasonable ways to checksum a file (at least on linux where I don't
care about binary mkode...)

Hope this helps,

Mike
-- 
mike@stok.co.uk                    |           The "`Stok' disclaimers" apply.
http://www.stok.co.uk/~mike/       | GPG PGP Key      1024D/059913DA 
mike@exegenix.com                  | Fingerprint      0570 71CD 6790 7C28 3D60
http://www.exegenix.com/           |                  75D2 9EC4 C1C0 0599 13DA