In this lesson, I've given you the basics of I/O and of managing file systems; the lessons you learn here should apply to all your basic Perl programs that need to use files and command-line arguments. On Day 17 we'll explore how to handle aspects of the file system itself. In this lesson's Going Deeper, I'll try and point you to a number of other places to look for more information and details about advanced input and output and handling filesystem features.
All the built-in Perl functions, as I've noted before, are documented in the perlfunc man page. Also of some use may be the FAQ on files and formats contained in the perlfaq man page.
A few other shortcuts and features of the open function: