Does $UploadDir == "/var/www/web/tmp/output/nu98382139012783/" ? If so, that's why the tar file is storing the full path.

To avoid this, you need to change the current working directory of where you are calling tar from, to the value of $UploadDir, and eliminate $UploadDir from the tar command, so it will operate on the local directory.

Is that what you want tar to do?

Check out the perl function "chdir" to effect that change within your script.