'download and convert' - script - PERL

We need a small Perl Script to download a file, unzip it and changing some of the contents of the files in the archive. 3 search and replace functions in all files and changing the contents of one file by creating single values from given intervals. This is a very easy script for an experienced perl programmer. It's very important to us, that the script doesn't need too much memory. There is no error handling necessary except stopping the script in case of an error. The script will be run from cron under Debian Linux every four months.