Widgets 1 : Button, Entry, Label

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".

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.

#!/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.

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.

#!/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");
}

This widget display text messages.

#!/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, ");
}