| This chapter presents a simple Tcl program that computes a Web page. The chapter provides a brief background to HTML and the CGI interface to Web servers. This chapter presents a complete, but simple guestbook program that computes an HTML document, or Web page, based on the contents of a simple database. The basic idea is that a user with a Web browser visits a page that is computed by the program. The details of how the page gets from your program to the user with the Web browser vary from system to system. The Tcl Web Server described in Chapter 18 comes with this guestbook example already set up. You can also use these scripts on your own Web server, but you will need help from your Webmaster to set things up. The chapter provides a very brief introduction to HTML and CGI programming. HTML is a way to specify text formatting, including hypertext links to other pages on the World Wide Web. CGI is a standard for communication between a Web server that delivers documents and a program that computes documents for the server. There are many books on these subjects alone. CGI Developers Resource, Web Programming with Tcl and Perl by John Ivler (Prentice Hall, 1997) is a good reference for details that are left unexplained here. A guestbook is a place for visitors to sign their name and perhaps provide other information. We will build a guestbook that takes advantage of the World Wide Web. Our guests can leave their address as a Universal Resource Location (URL). The guestbook will be presented as a page that has hypertext links to all these URLs so that other guests can visit them. The program works by keeping a simple database of the guests, and it generates the guestbook page from the database. The Tcl scripts described in this chapter use commands and techniques that are described in more detail in later chapters. The goal of the examples is to demonstrate the power of Tcl without explaining every detail. If the examples in this chapter raise questions, you can follow the references to examples in other chapters that do go into more depth. | 
