What is Tcl?

Tcl is a programming system developed by John Ousterhout at the University of California, Berkeley. (Dr. Ousterhout is now at Sun Microsystems.) According to Dr. Ousterhout:

Tcl is a simple scripting language for controlling and extending applications; its name stands for "tool command language". Tcl provides generic programming facilities, such as variables and loops and procedures, that are useful in a variety of applications. Furthermore, Tcl is embedable. Its interpreter is a library of C procedures that can easily be incorporated into applications, and each application can extend the core Tcl features with additional commands for that application.

When you write AOLserver extensions in Tcl, you use the core functionality of Tcl as well as a set of AOLserver-specific Tcl functions. For example, there is an AOLserver Tcl function called ns_conn that allows your Tcl script to obtain information about the current connection. In addition, functions are available for returning results to Web clients, accessing databases, and managing the permissions (access control) system.

This book describes the two different methods for extending AOLserver with Tcl, using AOLserver Dynamic Pages (Chapter 2) and Tcl libraries (see Chapter 3), plus general information on using Tcl with either method (see Chapter 4). It also provides a reference for AOLserver's Tcl API (see Chapter 5) and for the Tcl language (see Chapter 6).

Recommended Reading

For more information on the Tcl language, we recommend the following sources:

• Practical Programming in Tcl and Tk, by Brent B. Welch (Prentice Hall PTR, 1995)

• Tcl and the Tk Toolkit, by John K. Ousterhout (Addison-Wesley, 1994)

• Philip Greenspun's web site, http://www-swiss.ai.mit.edu/wtr/dead-trees/, which includes chapters from his book, Database Backed Web Sites, The Thinking Person's Guide to Web Publishing, and numerous examples of AOLserver Tcl database applications.

• The web site: http://www.yahoo.com/Computers_and_Internet/Programming_Languages/Tcl_Tk