From: Lloyd Zusman <ljz@...>
Date: 2002-10-05T15:38:40+09:00
Subject: Re: Ruby to approximate 'file'?

> Is there a file-type detection script available for Ruby, similar to 
> the unix 'file' program? At a minimum, is there a way in Ruby to 
> reliably tell the difference between a binary file format and a text 
> file format?

Here's something in Ruby that I wrote to do that.  It's based on the
algorithm that Perl uses to determine "textness" and "binariness":

 module FileTest

 private

   def self.isText(block)
      return (block.count("^ -~", "^\b\f\t\r\n") < (block.size / 3.0) &&
              block.count("\x00") < 1)
   end

 public

   # The textfile? and binaryfile? methods are not inverses of each
   # other.  Both return false if the item is not a file, or if the
   # item is a zero-length file.  The "textness" or "binariness" of
   # an item can only be determined if it's a file that contains at
   # least one byte.

   def self.textfile?(item)
     size = self.size(item)
     blksize = File.stat(item).blksize
     if size < 1 then
       return false
     end
     begin
       open(item) {
         |file|
         block = file.read(blksize < size ? blksize : size)
         return self.isText(block)
       }
     rescue
       return false
     end
   end

   def self.binaryfile?(item)
     size = self.size(item)
     blksize = File.stat(item).blksize
     if size < 1 then
       return false
     end
     begin
       open(item) {
         |file|
         block = file.read(blksize < size ? blksize : size)
         return !self.isText(block)
       }
     rescue
       return false
     end
   end
 end


> [ ... ]

-- 
 Lloyd Zusman
 ljz@asfast.com