The chapters in this section of the book, Chapters 8 through 14, are a functional reference. They describe how each PHP function works: what arguments are expected, what value is returned, and how they ought to be used. The functions are grouped generally by what they do.
Chapter 8 is concerned with communication with the browser. In addition to printing text, this chapter covers pregenerated variables and HTTP headers.
Chapter 9 discusses interaction with the operating system, including the local filesystem. There are functions for running other programs, functions for reading and writing files, and a collection of functions to help you debug your scripts.
Chapter 10 describes networking functions. There are functions ...