I had to replace one PHP script with a Perl CGI script not too long ago. PHP changed the data it presents to it's scripts that describe the filename of uploaded files (via a form input). The old behaviour was to provide the whole path to the file. The new behaviour provides only the filename (ie no path). This happened in a dot release and I could not find mention of it in the changelog. This is one of the main reasons I stopped developing in PHP.

Now I had a customer who had a Java program written to upload directories at a time via HTTP POST. His clients used it and logged in to his site which kept track of the uploads via PHP's session cookies. I had to fix it ASAP and I was not about to hack away at the PHP source or keep a custom patch to PHP for all future upgrades.

I needed to get Perl to read PHP's session files to keep track of who was uploading what files. PHP::Session made this really easy. I did however have to change a variable in the code. (save_path in Session.pm).