use warnings;
use strict;
use Tk;

my $mw = MainWindow->new;

my $index = 'Line: 1  -  Column: 0';

my $txt = $mw->Scrolled('Text',
    -scrollbars          => 'se',
    -wrap                => 'none',
    -background          => 'white',
    -width               => 40,
    -height              => 30,
    -selectbackground    => 'skyblue',
    -insertwidth         => 5,
    -borderwidth         => 3,
    -highlightcolor      => 'blue',      ### after visit
    -highlightbackground => 'red',       ### default before visit
    -padx                => 5,
    -pady                => 5,
)->pack();

my $label = $mw->Label( -textvariable => \$index )->pack();

$txt->bind( '<Key>', \&update_index );

MainLoop;

sub update_index {
    my ( $line, $column ) = split( /\./, $txt->index('insert') );
    $index = "Line: $line  -  Column: $column";
}