Two things: First, depending on the server configuration, the script may or may not be executing in the directory in which the file is installed. It's not where the script is installed that matters, but the current directory of the Perl process that's executing your script.

Second, more importantly: if you depend on a particular path, don't assume you're starting there, chdir to that directory explicitly. It guarantees your paths and has negligible overhead. If you're worried about spelling out the directory name in your script, read it in from the environment or some such. But don't assume your script will always execute in the same place.