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
Credits
About the Author
Acknowledgment
About the Reviewers
www.PacktPub.com
Preface

Controlling flow with the if statement


The if command evaluates a condition and if the condition evaluates to true, the actions are performed. The condition must be Boolean. With the addition of the else and elseif keywords, multiple conditions may be evaluated and numerous actions can be performed.

How to do it…

In the following recipe, we will create a Tcl script to be called from the command line that evaluates the argument passed, and based on the argument provided, perform an action.

Create a text file named if.tcl that contains the following commands:

# Set the variable x to the argument
set x [lindex $argv 0]
# Test for condition 1
if {$x == 1} {
puts "Condition 1 - You entered: $x"
# Test for condition 1
} elseif {$x == 2} {
puts "Condition 2 - You entered: $x"
# If neither condition is met perform the default action
} else {
puts "$x is not a valid argument"
}

Now invoke the script using the following command line:

tclsh85 if.tcl 1
Condition 1 - You entered: 1

How it works…

The if command...