Perl/Tutorial/Tk

Perl/Tk Tutorial - Create GUI with Perl's Tk Module

Introduction

Perl Programming Republic. Perl/Tk Tutorial - Create GUI with Perl's Tk Module

Perl/Tk (also known as pTk) is a collection of modules and code that attempts to wed the easily configured Tk 8 widget toolkit to the powerful lexigraphic, dynamic memory, I/O, and object-oriented capabilities of Perl 5. In other words, it is an interpreted scripting language for making widgets and programs with Graphical User Interfaces (GUI).

Perl or Practical Extraction and Report Language is described by Larry Wall, Perl's author, as follows: "Perl is an interpreted language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for any system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal)." The perlintro man page has this to say.

Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, web development, network programming, GUI development, and more.

Tk, the extension(or module) that makes GUI programming in perl possible, is taken from Tcl/Tk. Tcl(Tool Command Language) and Tk(ToolKit) was created by Professor John Ousterhout of the University of California, Berkeley. Tcl is a scripting language that runs on Windows, UNIX and Macintosh platforms. Tk is a standard add-on to Tcl that provides commands to quickly and easily create user interfaces. Later on Tk was used by a lot of other scripting languages like Perl, Python, Ruby etc.

Applications

Perl has been used since the early days of the web to write CGI scripts, and is now a component of the popular LAMP (Linux/Apache/MySQL/Perl) platform for web development. Perl has been called "the glue that holds the web together". Large systems written in Perl include Slashdot, and early implementations of Wikipedia and PHP.

Perl finds many applications as a glue language, tying together systems and interfaces that were not specifically designed to interoperate. Systems administrators use Perl as an all-purpose tool; short Perl programs can be entered and run on a single command line.

Philosophy

Perl has several mottos that convey aspects of its design and use. One is There's more than one way to do it (TMTOWTDI - usually pronounced 'Tim Toady'). Another is Perl: the Swiss Army Chainsaw of Programming Languages. A stated design goal of Perl is to "make easy tasks easy and difficult tasks possible".

Perl is free software, and may be distributed under either the Artistic or the GPL License. It is available for most operating systems but is particularly prevalent on Unix and Unix-like systems (such as Linux, FreeBSD, and Mac OS X), and is growing in popularity on Microsoft Windows systems.

Hello World

Let us begin, as all other tutorials begin, with the "Hello World" program. Create a file called "Hello.pl" and enter the following into it.

#!/usr/local/bin/perl
use Tk;
# Main Window
my $mw = new MainWindow;
my $label = $mw -> Label(-text=>"Hello World") -> pack();
my $button = $mw -> Button(-text => "Quit", 
		-command => sub { exit })
	-> pack();
MainLoop;

1. The first line - #!/usr/local/bin/perl is not needed in windows. In Linux, it tells the name of the script language processor. In our case it is perl. Don't understand what that means? Don't worry your gray cells over it. Just put it at the top of the file.
2. The second line - use Tk; tells the interpreter that our program will use the Tk module. This line is an absolute must in all GUI programs you make using perl. When the interpreter encounters this line, it will load the Tk components that we will be using to create our program.
3. The third line - This is a comment. Any line that starts with a '#' char is a comment. Comments are not of any use in the program. It is used by programmer to talk to themselves. A programmer cannot be expected to remember every thing a script does. So he uses a comment to write it down. Next time he edits the script, he can read the comment and understand what the program is for. It is good practice to make as much comments as possible.
4. The fourth line, my $mw = new MainWindow;, will create a window into which the GUI elements will be placed. The variable $mw is a object of type 'MainWindow'. We will have to use this element when we want to place any widget inside it.
5. The fifth line - $mw -> Label(-text=>"Hello World") -> pack(); makes a label and writes "Hello world" in it. You can change the text to any thing you like. Note the structure of the command '-'

Widget

A widget is a user interface object in X graphical user interfaces. Confused? Lets just say that it is the name of the object that appears on screen. There are many types widgets. If you want to display a button, you use the button widget. For text, you use the text widget. For entry, you guessed it, the entry widget. Syntax: my $WidgetVariable = $Window -> WidgetType(?Option 1=>Value 1, ?Option 2=>Value 2 ...??) -> pack();

Three things need to be said about widgets. First is the widget variable. This I have explained earlier. The widget variable of all widgets must be unique and will be used whenever that widget needs to be accessed. Second is the options. Each widget has some options which can be used to configure it. This is usually done when the widget is declared, but it can be done afterward also. The final thing is commands. Each widget has some commands which also can be used to configure it or make it do some thing.

But before we begin, we need to know a little about the pack command. I have explained this earlier but just doing it one more time so that you don't have to push the back button. Pack is a geometry manager. Another geometry manager is 'grid' - we will explore that latter. Pack is much more simpler than grid. The line $hello -> pack; tells the interpreter to pack the widget called "$hello".

Button

This will make a button. It can be configured to execute some code when the button is pushed. This will usually refer to a function so when the button is pushed, the function will run. An button is shown below. This button is created using HTML input tag.

Some Options

• -text=>"TEXT": TEXT will be the text displayed on the button
• -command=>CALLBACK: CALLBACK will be the code that is called when the button is pushed

#!/usr/local/bin/perl
use Tk;

# Main Window
my $mw = new MainWindow;

my $but = $mw -> Button(-text => "Push Me", 
		-command =>\&push_button);
$but -> pack();

MainLoop;

#This is executed when the button is pressed 
sub push_button {
	... whatever ...
}

You may have noticed that I used a slash(\) in the command callback (-command =>\&push_button);). Make sure that the slash stays there - to see why, go to the Most common mistakes by Perl/Tk beginners.

Entry

An entry is a widget that displays a one-line text string and allows the user to input and edit text in it. When an entry has the input focus it displays an insertion cursor to indicate where new characters will be inserted. An entry element is shown using HTML.

Some Options

• -width=>NUMBER: Width of the input field. NUMBER should be an integer.
• -textvariable=>\$VARIABLE: The contents of the variable VARIABLE will be displayed in the widget. If the text in the widget is edited, the variable will be edited automatically.
• -state=>STATE: The state of the input field. It can be normal, disabled, or readonly. If it is readonly the text can't be edited.

Some Commands

• $widget -> get();: The text inside input field can be taken by this command $name = $ent -> get();
• $widget -> delete(FIRST?,LAST?);: Delete one or more elements of the entry. FIRST is the index of the first character to delete, and LAST is the index of the character just after the last one to delete. If last isn't specified it defaults to FIRST+1, i.e. a single character is deleted. This command returns an empty string. $ent -> delete(0,'end');
• $widget -> insert(index,"STRING");: Insert the characters of STRING just before the character indicated by index. Index is 0 for the first character. The word "end" can be used for the last character $ent -> insert('end',"Hello");

Example

#!/usr/local/bin/perl
use Tk;

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my $ent = $mw -> Entry() -> pack();
my $but = $mw -> Button(-text => "Push Me", 
		-command =>\&push_button);
$but -> pack();

MainLoop;

#This is executed when the button is pressed 
sub push_button {
	$ent -> insert('end',"Hello");
}

Label

This widget display text messages. Some Options

• -text => "TEXT": TEXT will be the text displayed on the button
• -font => FONT: Specifies the font to use when drawing text inside the widget. You can specify just the font or you can give it in this format "FONTNAME SIZE STYLE". The STYLE can be bold, normal etc.

Example

#!/usr/local/bin/perl
use Tk;

my $mw = new MainWindow; # Main Window

my $lab = $mw -> Label(-text=>"Enter name:") -> pack();
my $ent = $mw -> Entry() -> pack();
my $but = $mw -> Button(-text => "Push Me", 
		-command =>\&push_button);
$but -> pack();

MainLoop;

#This is executed when the button is pressed
sub push_button {
	$ent -> insert(0,"Hello, ");
}

• $label - This variable assigned to that particular widget. Ever widget must have a UNIQUE variable. This name will be used when ever that widget must be accessed.
• $mw - $mw</nowiki> is the MainWindow's object. We will be placing our label widget inside this window.
• Label(-text=>"Hello World") - 'Label' is the name of the widget. A widget is a user interface object in X graphical user interfaces. Confused? Lets just say that it is the name of the object that appears on screen. There are many other widgets too. If you want to display a button, you use the button widget. For text, you use the text widget. For entry, you guessed it, the entry widget. If you want, you can see more about widgets.
• -text=>"Hello World" - The option for this widget. This option says that this widget must be given the text "Hello World". Options change according to the widgets - a button widget will not have all the options of the label widget and vise versa. But there will be many common ones.

Please note that operator used here is '=>' as opposed to the one used earlier '->' in $mw ->. One uses the minus(-) sign while the other uses the equals(=) sign. Do not confuse between these two. You can keep writing other options can also be written here. For example, let us make a label for showing the text "Hello World". The other lines are same as the Hello World program. $mw -> Label(-text=>"Hello World",-font=>"courierfont",-relief=>"raised") -> pack();

In this example, a lot more options are used. The font option is used to tell which font must be used to make the text and the relief option tells whether the text should appear raised, sunken, flat etc. To know all the options for a particular widget, read the manual that comes with Perl. It lists every widget and every option they have. If you are going to program in Perl, you will find your self peeking into the manual every few minutes. The most important and most commonly used options are listed here.

All options must separated by a comma. But as you have noted, this line is a little difficult to read. As the number of options increase, the more difficult to read it. So a more readable version is...

$mw -> Label(-text=>"Hello World",
		-font=>"courierfont",
		-relief=>"raised") 
	-> pack();

Next comes the -> pack();. This will pack the widget '$label' into the window '$mw'. 'pack' is a geometry manager. Another geometry manager is 'grid'. Personally, I like grid better. Once again, putting all this in one line is an eye sore - so you can put this part in the next line.

my $label = $mw -> Label(-text=>"Hello World")
	-> pack();

In this case, pack has no options within it. But that is not always the case.

my $label = $mw -> Label(-text=>"Hello World")
	-> pack(-side=>"left",
		-anchor=>'w');

You don't have to pack the widget in the same line of creating it - but it is convenient in small programs. You can pack the widget later using the widget's variable. For example...

my $label = $mw -> Label(-text=>"Hello World"); #We created the widget
$label -> pack(-side=>"left", -anchor=>'w'); #We pack it in another line

So we have the final syntax of how to create and display a widget... my $WidgetVariable = $Window -> WidgetType(?Option 1=>Value 1, ?Option 2=>Value 2 ...??) -> pack();

The next three lines...

my $button = $mw -> Button(-text => "Quit", 
		-command => sub { exit })
	-> pack();

will create and display a button. Here the widget variable is '$button'. When we look at the options, we will find two options - 'text' and 'command'. The given text is Quit - so the button will have the text "Quit" on it. The command option determines what should happen when the user click on the button. You can specify a function to execute when the user clicks on the button. In this case the program will exit when this button is pressed. One can also call functions that you have created from here...

#!/usr/local/bin/perl

use Tk;
# Main Window
my $mw = new MainWindow;
my $label = $mw -> Label(-text=>"Hello World") -> pack();
my $button = $mw -> Button(-text => "Quit", 
		-command =>\&exitProgam)
	-> pack();
MainLoop;

sub exitProgam {
 	$mw->messageBox(-message=>"Goodbye");
	exit;
}

The next line - MainLoop; is the Main Loop or the Event Loop. Its job is to invoke callbacks in response to events such as button presses or timer expirations. If this line is missing, the program will run and exit with out waiting for the user to do any thing. This is another one of those 'absolute musts' of Perl/Tk programming.

Now Perl puritans will raise a great hue and cry and say that this is not the way to print "Hello World". The "pure" method is the following...

#!/usr/local/bin/perl
print "Hello World"

Putting things in perspective, I am teaching Perl/Tk - not Perl. The above is the Perl method of doing it. My method is the pTk method of doing it.

Frame

A frame is a simple widget. Its primary purpose is to act as a spacer or container for complex window layouts. The only features of a frame are its background color and an optional 3-D border to make the frame appear raised or sunken. Frame can be created just like any other widget - my $frm = $mw -> Frame(); To place other widgets in this frame, you should use the frame widget variable as its parent. Normally the parent is '$mw' or the MainWindow. But if we wish to put a widget inside a frame, use the frame variable('$frm' in this case) in place of '$mw'. Like this... my $lab = $frm_name -> Label(-text=>"Name:") -> pack(); Some Options

• -relief=>STYLE: Specifies the 3-D effect desired for the widget. Acceptable values are raised, sunken, flat, ridge, solid, and groove. The value indicates how the interior of the widget should appear relative to its exterior; for example, raised means the interior of the widget should appear to protrude from the screen, relative to the exterior of the widget.

Example

#!/usr/local/bin/perl
use Tk;

my $mw = new MainWindow; # Main Window

my $frm_name = $mw -> Frame() -> pack(); #New Frame
my $lab = $frm_name -> Label(-text=>"Name:") -> pack();
my $ent = $frm_name -> Entry() -> pack();

my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button) -> pack();

MainLoop;

#This function will be executed when the button is pushed
sub push_button {
	$ent -> insert(0,"Hello, ");
}

Text

A text widget displays one or more lines of text and allows that text to be edited. Similar to the entry widget but a larger version of it.

Some Options

• -xscrollcommand => COMMAND: This is to enable communication between a text widget and a scroll bar widget. There is a -yscrollcommand similler to this one.
• -font => FONTNAME: Specifies the font to use when drawing text inside the widget.
• -width => NUMBER: Specifies the width of the widget
• -height => NUMBER: Specifies the, you guessed it, height of the widget

Some Commands

• $widget -> get(index1, ?index2 ...?);: Return a range of characters from the text. The return value will be all the characters in the text starting with the one whose index is index1 and ending just before the one whose index is index2 (the character at index2 will not be returned). If index2 is omitted then the single character at index1 is returned.
  Note that the index of text is different from that of the entry widget. The index of text widget is in the form LINE_NO.CHARECTER_NO. This means that 1.0 means the first character in the first line. $contents = $txt -> get(1.0,'end');
• $widget -> insert(index,DATA);: Inserts all of the chars arguments just before the character at index. If index refers to the end of the text (the character after the last newline) then the new text is inserted just before the last newline instead. $txt -> inset('end',"Hello World");

Example

#!/usr/local/bin/perl
use Tk;

my $mw = new MainWindow; # Main Window

my $frm_name = $mw -> Frame() -> pack();
my $lab = $frm_name -> Label(-text=>"Name:") -> pack();
my $ent = $frm_name -> Entry() -> pack();

my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button) -> pack();
#Text Area
my $txt = $mw -> Text(-width=>40, -height=>10) -> pack();

MainLoop;

#This function will be executed when the button is pushed
sub push_button {
	my $name = $ent -> get();
	$txt -> insert('end',"Hello, $name.");
}

Scrollbar

A scroll bar is a widget that displays two arrows, one at each end of the scroll bar, and a slider in the middle portion of the scroll bar. It provides information about what is visible in an associated window that displays an document of some sort (such as a file being edited or a drawing). The position and size of the slider indicate which portion of the document is visible in the associated window. For example, if the slider in a vertical scroll bar covers the top third of the area between the two arrows, it means that the associated window displays the top third of its document. It is made to work with other widgets like text.

Some Options

• -orient=>DIRECTION: For widgets that can lay themselves out with either a horizontal or vertical orientation, such as scroll bars, this option specifies which orientation should be used. DIRECTION must be either horizontal or vertical or an abbreviation of one of these.
• -command => COMMAND: This command gets executed when the scroll bar is moved. This option almost always has a value such as .t xview or .t yview, consisting of the name of a widget and either xview (if the scroll bar is for horizontal scrolling) or yview (for vertical scrolling). All scrollable widgets have xview and yview commands that take exactly the additional arguments appended by the scroll bar.

Example

#!/usr/local/bin/perl
use Tk;

my $mw = new MainWindow; # Main Window

my $frm_name = $mw -> Frame();
my $lab = $frm_name -> Label(-text=>"Name:");
my $ent = $frm_name -> Entry();

my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button);

my $textarea = $mw -> Frame(); #Creating Another Frame
my $txt = $textarea -> Text(-width=>40, -height=>10);
my $srl_y = $textarea -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $textarea -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y], 
		-xscrollcommand=>['set',$srl_x]);

$lab -> grid(-row=>1,-column=>1);
$ent -> grid(-row=>1,-column=>2);
$frm_name -> grid(-row=>1,-column=>1,-columnspan=>2);

$but -> grid(-row=>4,-column=>1,-columnspan=>2);

$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$textarea -> grid(-row=>5,-column=>1,-columnspan=>2);

MainLoop;

#This function will be executed when the button is pushed
sub push_button {
	my $name = $ent -> get();
	$txt -> insert('end',"Hello, $name.");
}

grid

As you can see I have used 'grid' here. Grid is NOT a widget. It is a geometry manager like pack but more advanced. Lets take a closer look at the commands - $widget -> grid(-row=>1, -column=>1); This line will tell the interpreter to put the widget called '$txt' in the first row of the first column of its parent widget. The below digram will help you understand.

	Column 1	Column 2
Row 1	$txt widget will be here	$srl_y widget's place
Row 2	$srl_x widget's position

Some Options

• -sticky => STYLE: This option may be used to position (or stretch) the widget within its cell. STYLE is a string that contains zero or more of the characters n, s, e or w. Each letter refers to a side (north, south, east, or west) that the slave will "stick" to. If both n and s (or e and w) are specified, the slave will be stretched to fill the entire height (or width) of its cavity.
• -ipadx => AMOUNT: The AMOUNT specifies how much horizontal internal padding to leave on each side of the slave(s). This is space is added inside the slave(s) border.
• -ipady => AMOUNT: The AMOUNT specifies how much vertical internal padding to leave on each side of the slave(s). Options same as -ipadx
• -padx => AMOUNT: The amount specifies how much horizontal external padding to leave on each side of the slave(s), in screen units. AMOUNT may be a list of two values to specify padding for left and right separately.
• -pady => AMOUNT: The amount specifies how much vertical external padding to leave on the top and bottom of the slave(s), in screen units. Options same as -padx.
• -row => N : Insert the slave so that it occupies the Nth row in the grid. Row numbers start with 0. If this option is not supplied, then the slave is arranged on the same row as the previous slave specified on this call to grid, or the first unoccupied row if this is the first slave.
• -column => N: Insert the slave so that it occupies the N'th column in the grid. Options same as -row
• -rowspan => N: Insert the slave so that it occupies N rows in the grid. The default is one row.
• -columnspan => N: Insert the slave so that it occupies N columns in the grid.

Using grid requires a bit of experience - but if you know HTML it would help a lot. The rows and columns are just like those in HTML tables - although the codes are very different.

Scale

Makes a slider that can be adjusted by the user to input a variable.

Some Options

• -from => NUMBER: Starting Number
• -to => NUMBER: Ending Number
• -tickinterval => NUMBER: Determines the spacing between numerical tick marks displayed below or to the left of the slider.
• -varable => NAME: Specifies the name of a global variable to link to the scale. Whenever the value of the variable changes, the scale will update to reflect this value. Whenever the scale is manipulated interactively, the variable will be modified to reflect the scale's new value.

Some Commands

• $widget -> get();: Get the current value of the scale my $age = $scl -> get();
• $widget -> set(value);: Give the scale a new value. $scl -> set(20);

Example

#!/usr/local/bin/perl
use Tk;

#Global Variables
my $age = 10;

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my $frm_name = $mw -> Frame();
my $lab = $frm_name -> Label(-text=>"Name:");
my $ent = $frm_name -> Entry();
#Age
my $scl = $mw -> Scale(-label=>"Age :",
	 -orient=>'v',	 	-digit=>1,
	 -from=>10,		-to=>50,
	 -variable=>\$age,	-tickinterval=>10);

my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button);

#Text Area
my $textarea = $mw -> Frame();
my $txt = $textarea -> Text(-width=>40, -height=>10);
my $srl_y = $textarea -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $textarea -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y], 
		-xscrollcommand=>['set',$srl_x]);

#Geometry Management
$lab -> grid(-row=>1,-column=>1);
$ent -> grid(-row=>1,-column=>2);
$scl -> grid(-row=>2,-column=>1);
$frm_name -> grid(-row=>1,-column=>1,-columnspan=>2);

$but -> grid(-row=>4,-column=>1,-columnspan=>2);

$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$textarea -> grid(-row=>5,-column=>1,-columnspan=>2);

MainLoop;

## Functions
#This function will be exected when the button is pushed
sub push_button {
	my $name = $ent -> get();
	$txt -> insert('end',"$name is $age years old.");
}

Now our little example is becoming more and more like a program. We have added the comments to it as it has grown big and is difficult to understand. Now we have added a slider with which age can be inputed.

Radiobutton

Radiobutton is an input where any one of many choices MUST be chosen. If one is chosen and another button is clicked, the last chosen will lose its state and the clicked button will be chosen. A graphic example(in HTML) is given below. Choices 1 | 2 | 3

Some Options

• -command=>COMMAND: Specifies a command to associate with the button. This command is typically invoked when mouse button 1 is released over the button window.
• -variable => \$VARIABLE: Specifies name of global variable to set to indicate whether or not this button is selected.
• -value => VALUE: Specifies value to store in the button's associated variable whenever this button is selected.

Some Commands

• $widget -> deselect();: Deselects the checkbutton and sets the associated variable to its "off" value. $rdb_m -> deselect();
• $widget -> select(): Selects the checkbutton and sets the associated variable to its "on" value. $rdb_m -> select();

Example

#!/usr/local/bin/perl
use Tk;

#Global Variables
my $age = 10;
my $gender = "Male";

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my $frm_name = $mw -> Frame();
my $lab = $frm_name -> Label(-text=>"Name:");
my $ent = $frm_name -> Entry();
#Age
my $scl = $mw -> Scale(-label=>"Age :",
	 -orient=>'v',	 	-digit=>1,
	 -from=>10,		-to=>50,
	 -variable=>\$age,	-tickinterval=>10);

#Gender
my $frm_gender = $mw -> Frame();
my $lbl_gender = $frm_gender -> Label(-text=>"Sex ");
my $rdb_m = $frm_gender -> Radiobutton(-text=>"Male",  
		-value=>"Male",  -variable=>\$gender);
my $rdb_f = $frm_gender -> Radiobutton(-text=>"Female",
		-value=>"Female",-variable=>\$gender);


my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button);

#Text Area
my $textarea = $mw -> Frame();
my $txt = $textarea -> Text(-width=>40, -height=>10);
my $srl_y = $textarea -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $textarea -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y],
		-xscrollcommand=>['set',$srl_x]);

#Geometry Management
$lab -> grid(-row=>1,-column=>1);
$ent -> grid(-row=>1,-column=>2);
$scl -> grid(-row=>2,-column=>1);
$frm_name -> grid(-row=>1,-column=>1,-columnspan=>2);

$lbl_gender -> grid(-row=>1,-column=>1);
$rdb_m -> grid(-row=>1,-column=>2);
$rdb_f -> grid(-row=>1,-column=>3);
$frm_gender -> grid(-row=>3,-column=>1,-columnspan=>2);

$but -> grid(-row=>4,-column=>1,-columnspan=>2);

$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$textarea -> grid(-row=>5,-column=>1,-columnspan=>2);

MainLoop;

## Functions
#This function will be executed when the button is pushed
sub push_button {
	my $name = $ent -> get();
	$txt -> insert('end',"$name\($gender\) is $age years old.");
}

This time the program is subjected to even more change - the geometry manager is fully grid now. There is no instances of pack. You will find this necessary when the layout becomes more complicated. I hope you can stay with me in such trying times.

Checkbutton

Checkbotton is a input with two options - Off or On - it has to be either one. The state can be changed by clicking on it. An example is shown below. check box

Some Options

• -offvalue=>VALUE: Specifies value to store in the button's associated variable whenever this button is deselected. Defaults to ``0.
• -onvalue=>VALUE: Specifies value to store in the button's associated variable whenever this button is selected. Defaults to ``1.
• -command=>CALLBACK: Specifies a command to associate with the button. This command is typically invoked when mouse button 1 is released over the button window.
• -variable=>\$VARABLE: Specifies name of global variable to set to indicate whether or not this button is selected.

Some Commands

• $widget -> deselect();: Deselects the checkbutton and sets the associated variable to its ``off value. $chk -> deselect();
• $widget -> select();: Selects the checkbutton and sets the associated variable to its ``on value. $chk -> select();
• $widget -> toggle();: Toggles the selection state of the button, redisplaying it and modifying its associated variable to reflect the new state. $chk -> toggle();

Example

#!/usr/local/bin/perl
use Tk;

#Global Variables
my $age = 10;
my $gender = "Male";
my $occupied = 1;

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my $frm_name = $mw -> Frame();
my $lab = $frm_name -> Label(-text=>"Name:");
my $ent = $frm_name -> Entry();
#Age
my $scl = $mw -> Scale(-label=>"Age :",
	 -orient=>'v',	 	-digit=>1,
	 -from=>10,		-to=>50,
	 -variable=>\$age,	-tickinterval=>10);
	
#Jobs
my $chk = $mw -> Checkbutton(-text=>"Occupied",
	-variable=>\$occupied);
$chk -> deselect();

#Gender
my $frm_gender = $mw -> Frame();
my $lbl_gender = $frm_gender -> Label(-text=>"Sex ");
my $rdb_m = $frm_gender -> Radiobutton(-text=>"Male",  
		-value=>"Male",  -variable=>\$gender);
my $rdb_f = $frm_gender -> Radiobutton(-text=>"Female",
		-value=>"Female",-variable=>\$gender);

my $but = $mw -> Button(-text=>"Push Me", -command =>\&push_button);

#Text Area
my $textarea = $mw -> Frame();
my $txt = $textarea -> Text(-width=>40, -height=>10);
my $srl_y = $textarea -> Scrollbar(-orient=>'v',-command=>[yview => $txt]);
my $srl_x = $textarea -> Scrollbar(-orient=>'h',-command=>[xview => $txt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y], 
		-xscrollcommand=>['set',$srl_x]);

#Geometry Management
$lab -> grid(-row=>1,-column=>1);
$ent -> grid(-row=>1,-column=>2);
$frm_name -> grid(-row=>1,-column=>1,-columnspan=>2);

$scl -> grid(-row=>2,-column=>1);
$chk -> grid(-row=>2,-column=>2,-sticky=>'w');

$lbl_gender -> grid(-row=>1,-column=>1);
$rdb_m -> grid(-row=>1,-column=>2);
$rdb_f -> grid(-row=>1,-column=>3);
$frm_gender -> grid(-row=>3,-column=>1,-columnspan=>2);

$but -> grid(-row=>4,-column=>1,-columnspan=>2);

$txt -> grid(-row=>1,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$textarea -> grid(-row=>5,-column=>1,-columnspan=>2);

MainLoop;

## Functions
#This function will be executed when the button is pushed
sub push_button {
	my $name = $ent -> get();
	$txt -> insert('end',"$name\($gender\) is $age years old.");
}