In this chapter, you learned how to use the include() family of functions (include_once(), require(), and require_once() thrown in for good measure) to incorporate files into your documents and to execute any PHP code contained in include files. You learned how to use some of PHP's file testing functions, and explored functions for reading files by the line, by the character, and in arbitrary chunks. You learned how to write to files, by either replacing or appending to existing content. Finally, you learned how to create, remove, and read directories.
Now that you can work with the filesystem a little more, you can save and access substantial amounts of data. If you need to look up data from large files, however, such scripts begin to slow down quite considerably. When that occurs, you should look into a database system, which will be coming your way shortly!