Handling String Expressions | Tcl/Tk 8.5 Programming Cookbook

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Tcl/Tk 8.5 Programming Cookbook

3 (7)

Tcl/Tk 8.5 Programming Cookbook

3 (7)

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.

Tcl/Tk 8.5 Programming Cookbook

Tcl/Tk 8.5 Programming Cookbook

Credits

Credits

About the Author

About the Author

Acknowledgment

Acknowledgment

About the Reviewers

About the Reviewers

www.PacktPub.com

www.PacktPub.com

Preface

Preface

Free Chapter

The Tcl Shell

The Tcl Shell

Introduction

The Tcl shell

Writing to the Tcl console

Mathematical expressions

Tcl expr operands

Mathematical functions

Computing mathematical expressions

Referencing files in Tcl

Variables

Command line arguments

Using the Building Blocks Control Constructs

Using the Building Blocks Control Constructs

Introduction

Controlling flow with the if statement

Looping with for

Looping with foreach

Looping with while

Continuing a procedure

Breaking out of a procedure

Nested looping

Error Handling

Error Handling

Introduction

Using the catch command

Using the eval command

Using the error command

Error handling procedure

Handling String Expressions

Handling String Expressions

Introduction

Appending to a string

Formatting a string

Matching a regular expression within a string

Performing character substitution on a string

Parsing a string using conversion specifiers

Determining the length of a string

Comparing strings

Comparing a string of characters

Locating the first instance of a character

Locating the index of a character

Determining the class of a string

Locating the last instance of a string

Determining the size of a string

Replacing values within a string

Locating a pattern within a string

Returning a range of characters from a string

Creating a string of repeated characters

Replacing ranges of characters contained within a string

Creating a reverse string

Converting a string to lowercase

Converting a string to title

Converting a string to uppercase

Trimming a string

Trimming leading whitespace

Trimming trailing whitespace

Locating the word end

Locating the word start

Performing variable substitution

Expanding String Functionality Using Lists

Expanding String Functionality Using Lists

Introduction

Creating a list

Joining two lists

Joining list elements

Appending list elements

Assigning list elements to variables

Retrieving an element from a list

Inserting elements into a list

Determining the number of elements

Getting a list element

Repeating elements

Replacing elements

Reversing elements

Searching a list

Editing a list

Sorting a list

Splitting a string into a list

The Tcl Dictionary

The Tcl Dictionary

Introduction

Creating a dictionary

Appending to a dictionary

Determining if a key exists

Filtering a dictionary

Searching a dictionary

Getting a record

Incrementing a value

Getting the dictionary structure

Getting a list of keys

Appending to an existing record

Merging two dictionaries

Creating a blank dictionary structure

Updating variables from a dictionary

Determining the size of a dictionary

Getting all records

Assigning values

File Operations

File Operations

Introduction

Opening a file

Configuring a file

Opening a command pipeline

Writing a file

Reading a file

Closing a file

File handling

Tk GUI Programming with Tcl/Tk

Tk GUI Programming with Tcl/Tk

Introduction

Creating a widget

Writing to the console

Setting the attributes of the window through window manager

Creating an additional window

Configuring and Controlling Tk Widgets

Configuring and Controlling Tk Widgets

Introduction

Creating a frame widget

Creating a label widget

Creating an entry widget

Creating a button widget

Creating a listbox widget

Creating an image

Creating a simple form

Geometry Management

Geometry Management

Introduction

Controlling layout with the pack command

Controlling layout with the grid command

Combining pack and grid

Creating an address book interface

Using Tcl Built-in Dialog Windows

Using Tcl Built-in Dialog Windows

Introduction

Displaying a message box

Displaying a confirmation dialog

Displaying the color picker

Displaying the directory dialog

Displaying the file selection dialog

Selecting a directory and file

Creating and Managing Menus

Creating and Managing Menus

Introduction

Creating a menu

Adding menu buttons

Displaying a pop-up menu

Data entry application

Creating the Address Book Application

Creating the Address Book Application

Introduction

Creating the Address Book application

Adding a record

Navigating records

Deleting a record

Finding a record

Full listing

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:

Switch	Description
`-nobackslashes`	No backslash substitution will be performed.
`-nocommands`	No command substitution will be performed.
`-novariables`	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...

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