Book Image

Tcl/Tk 8.5 Programming Cookbook

Book Image

Tcl/Tk 8.5 Programming Cookbook

Overview of this book

With Tcl/Tk, you can create full-featured cross-platform applications in a simple and easy-to-understand way without any expensive development package; the only tools required are a simple text editor and your imagination. This practical cookbook will help you to efficiently interact with editors, debuggers, and shell type interactive programs using Tcl/Tk 8. This cookbook will comprehensively guide you through practical implementation of Tcl/Tk 8.5 commands and tools. This book will take you through all the steps needed to become a productive programmer in Tcl/Tk 8. Right from guiding you through the basics to creating a stand-alone application, it provides complete explanation of all the steps along with handy tips and tricks. The book begins with an introduction to the Tcl shell, syntax, variables, and programming best practices in the language. It then explores procedures and the flow of events with control constructs followed by advanced error trapping and recovery. From Chapter 4, a detailed study of string expressions and handling enables you to handle various string functions and use lists to expand the string functionality. The book then discusses in-depth the Tcl Dictionary and how to utilize it to store and retrieve data. File operations and Tk GUI handling are covered extensively along with a developing a real-world address book application to practice the concepts learned.
Table of Contents (20 chapters)
Tcl/Tk 8.5 Programming Cookbook
About the Author
About the Reviewers

Performing variable substitution

Now that we have mapped, formatted, counted, analyzed, and generally picked our strings apart, let's look at programmatically performing variable substitution in a string. As Tcl always seems to do, we have been provided with a powerful command to simplify the task with the subst command. While you could easily invoke the set command to change the contents, subst provides the ability to alter portions of a variable by providing optional switches.

The syntax of the subst command is as follows:

subst switch string

The subst command performs variable substitution to a string. The behavior may be controlled with optional switches.

These switches are as follows:




No backslash substitution will be performed.


No command substitution will be performed.


No variable substitution will be performed.

How to do it…

In the following example, we will create a string that contains the value of a variable...