New Novice has asked for the wisdom of the Perl Monks concerning the following question:

Enlightened Ones,

I downloaded a (huge) number of webpages from the internet using a perl routine some time ago. Now I want to check if there are any files that I missed or that are new.

It is actually more complicated than this (as I have to retrieve information from a database first, open up webpages and then extract bits and pieces from the resulting pages). What it boils down to, however, is that I have a list of the files on my computer and that I can generate a list of the webpages. I can link these two by a common piece of information (there is an ID-number on the webpages, which I use to construct the file name). Now the question is, how do I create a third list that gives me all the webpages that my new search of the database returned but which I haven't downloaded yet (i.e., are not contained in the list of files). How can I compare the elements in two lists with a view to elements that are contained in one but not the other.

Go with Perl!

Many Thanks in advance!