| In this chapter, we moved away from the design of traditional HTML pages and looked at what we could do with server-side programming. You saw the differences between client-side programming, using JavaScript or Flash, and server-side programming using CGI or an application server. You also learned about the situations in which it is appropriate to use each technology. By understanding the way that the common gateway interface (CGI) works, you can see how potentially powerful it can be. By learning to program the way the server responds to users, you can give different responses to different users, based on the type of browser they are using, the way they fill in forms on your Web site, and even depending on the time of day! Different languages can be used to create CGI programs, but the most common is Perl. You looked at Perl quickly so that you would be able to understand the basics of a Perl program, even if you are unable to write a full program yourself. Many Web sites provide prewritten Perl programs for you to use. To show how this can be achieved very easily, you downloaded a prewritten Perl script for a guest book, modified it for your own server setup, and installed it on your Web site. You also looked at Java, a programming language which straddles the divide between client-side and server-side programming. Java is a complicated language to learn, although potentially very powerful. However, you can use Java programs that others have written and make available for use often for free. You used a small, client-side Java program, called an applet, to provide a chat room on your Web site. | 
