This short programme demonstrates how to change font size. I hope it can help you. 
#!/usr/bin/perl
use warnings;
use strict;

use Tk;
use Tk::Font;

sub change {
    my ($size_ref, $change, $l) = @_;
    $$size_ref += $change;
    $l->configure(-font => $l->fontCreate(-size => $$size_ref));
}


my $mw    = 'MainWindow'->new(-title => 'Scalable');

my $size  = 12;
my $font  = $mw->fontCreate(-size => $size);
my $l     = $mw->Label(-text => 'Some text', -font => $font)->pack;

my $f     = $mw->Frame->pack;
my $plus  = $f->Button(-text => '+', -command => [\&change, \$size,  1
+, $l])->pack(-side => 'left');
my $minus = $f->Button(-text => '-', -command => [\&change, \$size, -1
+, $l])->pack(-side => 'right');

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

MainLoop();

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: how to change the font of a perl tk gui by choroba
in thread how to change the font of a perl tk gui by ghosh123

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