def digest_sha1(*files)
      files.flatten.collect { |file| 
        File.exists?(file) ? Digest::SHA1.hexdigest(File.read(file)) : nil
      }
    end
def digest_sha1(*files)
      files.flatten.collect { |file| 
        File.exists?(file) ? Digest::SHA1.hexdigest(File.read(file)) : nil
      }
    end
* +files+ An Array of file paths
 Returns an Array of SH1 digests for each of the given files