zip?(file)
Checks if file is a zip file in disguise. Signatures from http://www.garykessler.net/library/file_sigs.html
# File lib/rdoc/parser.rb, line 93 def self.zip? file zip_signature = File.read file, 4 zip_signature == "PK\x03\x04" or zip_signature == "PK\x05\x06" or zip_signature == "PK\x07\x08" rescue false end