Unpacking binary data in PHP
Working with binary files in PHP is rarely a requirement. However when needed the PHP ‘pack’ and ‘unpack’ functions can help you tremendously. To set the stage we will start with a programming problem, this will keep the discussion anchored to a relevant context. The problem is this : We want to write a function that takes a image file as an argument and tells us whether the file is a GIF image; irrelevant with whatever the extension the file may have. We are not to use any GD library functions.