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

Getting a list element

As we can now determine the number of elements contained within a list, it is time to retrieve one or more of those elements. To accomplish this, Tcl provides the lrange command. The syntax is as follows:

lrange list first last

How to do it…

In the following example, we will pass a list to the lrange command to retrieve the elements contained with the indices provided. Return values from the commands are provided for clarity. Enter the following command:

% lrange {John Mary Bill Fred Tom Sally} 0 1
John Mary

How it works…

The lrange command accepts a valid Tcl list and returns a new list consisting of the elements referenced in the index values provided in first and last last inclusive. If the index contained in first is less than 0, it is treated as 0. If the index contained in last is greater than or equal to the number of elements, it is treated as if it were end, as described previously, where indexes are concerned.