Which cpan modules are the best to read and study?

I learned quite a bit (tie-ing, platform independent filesystem access, etc) by reading the code for File::chdir. It is also a very handy module to use in your scripts, I use it all the time.

I would also add to bvr's list: read the source for modules that you use frequently, since you are already familiar with their expected behavior, you can more clearly see what is being done to achieve that result.

The question is what you want to learn, but it is certainly good idea to study various modules, because you learn to read other people code and learn various tricks. Some random recommendations I can think of

• start with smaller modules with clear interface you know and are interested in
• once you feel familiar with organization of modules and basics, try something larger
• try rather newer modules
• look into test suite and into examples
• if you don't understand specific piece, try to make reduced example a play with it

It is hard to recommend something specific, but I liked my recent look into Web::Scraper module.