From: Mike Stok <mike@...>
Date: 2006-03-22T08:59:42+09:00
Subject: Re: Newbie: Better way to check a magic number on a file?


On 21-Mar-06, at 6:46 PM, Wes Gamble wrote:

> All,
>
> I am trying to determine if I am dealing with an Excel file that I
> upload to a Web server.
>
> Here is the first test - to verify the magic number of the file that I
> have:
>
> #Check the magic number first to see if it's even an Office file
>
>     magic_number = nil
>     File.open(path_to_file, "r") do |f|
>       magic_number = f.read(6)
>     end
>     return false unless
> magic_number.unpack('H*').to_s().eql?('d0cf11e0a1b1')
>
> This seems a little bit less than optimal.  I have to unpack my string
> into an array and then reconvert it back to a string to compare it?
>
> Surely there is a simpler way?
>
> Should magic_number.eql?('d0cf11e0a1b1') work?

There are a number of simpler ways, one might be

   EXCEL_FILE_MAGIC_NUMBER = ['d0cf11e0a1b1'].pack('H*')

   # later

   magic_number == EXCEL_FILE_MAGIC_NUMBER # => true or false

or you can use octal or hex escapes to have a string literal to  
compare against e.g.

irb(main):006:0> "\320\317\021\340\241\261" == "\xd0\xcf\x11\xe0\xa1 
\xb1"
=> true

Maybe there are good bits of the Pickaxe (Programming Ruby) or some  
on-line tutorials which can help you see some of the more ruby-ish  
ways to do things.

Hope this helps,

Mike

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.