Hi. I got some code from this site that demonstrates "-textvariable" usage. However, there are some basic questions I have about it's operation. The code is; 

 
#!/usr/bin/perl

use strict;
use warnings;

use Tk;
use POSIX;

my $red;
my $green;
my $blue;

my $mw = MainWindow->new;
$mw->geometry('300x100');   # x amount then y amount
$mw->title('Raw Renamer');

# A frame for labels on the left hand size
my $left_frame = $mw->Frame (-borderwidth => 2, -relief => 'groove')
                            ->pack(-side   => 'left',
                                   -anchor => 'n',
                                   -expand => 1);
                                   
my $text_label = $left_frame->Label->pack(-side => 'left',       # Why
+ this ?
                                          -anchor => 'n',
                                          -expand => 1);

$text_label->Label(-text =>"Red")->pack(  -side   => 'top',
                                          -anchor => 'w');
$text_label->Label(-text =>"Green")->pack(-side   => 'top',
                                          -anchor => 'w');
$text_label->Label(-text =>"Blue")->pack( -side   => 'top',
                                          -anchor => 'w');

# Another frame for the ($red $green $blue) variables
my $variable_frame = $mw->Frame (-borderwidth => 4, -relief => 'groove
+')
                               ->pack(-side   => 'left',
                                      -anchor => 'n',
                                      -expand => 1);

my $red_label   = $variable_frame->Label(-textvariable =>\$red)  ->pac
+k(-side => 'top');
my $green_label = $variable_frame->Label(-textvariable =>\$green)->pac
+k(-side => 'top');
my $blue_label  = $variable_frame->Label(-textvariable =>\$blue) ->pac
+k(-side => 'top');

Intialize();                # How is this infinite loop bypassed ?
MainLoop;

sub Intialize
{
    print "Str";
    while(1)
    { 
        print ".";
        $red  = floor(50*rand());
        $red_label->update;
        sleep 2;
        
        $green = floor(50*rand()+50);
        $green_label->update;
        sleep 2;
        
        $blue = floor(50*rand()+100);
        $blue_label->update;
        sleep 2;
    }
}

[download]

The line "my $text_label" seems to be half a declaration that is used in an anonymous fashion in the subsequent 3 labels. Is this the case ?. I tried removing the "pack" part expecting that this is not required. But it is required.

Next, the call "Intialize();" should get stuck in an infinite loop. But it does not and the program runs OK? and the "MainLoop;" gives a display screen.

Regard JC.......

In reply to Basic questions of Tk programming by jmClifford

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