use strict;
use warnings;
use Tk;

my $t     = time;
my $ts    = update_time($t);
my $mw    = MainWindow->new();
my $label = $mw->Label( -textvariable => \$ts, )
  ->grid( -row => 1, -column => 1, -columnspan => 3, );

my %button;
# Fixed    - will display time when button was created
# Variable - will display current time
$button{fixed} = $mw->Button(
    -text    => q{Fixed},
    -command => [ \&update_time, $t, ],
)->grid( -row => 2, -column => 1, );
$button{variable} = $mw->Button(
    -text    => q{Variable},
    -command => sub { $t = time; &update_time( $t, ); },
)->grid( -row => 2, -column => 2, );
$button{exit} = $mw->Button(
    -text    => q{Exit},
    -command => sub { exit; },
)->grid( -row => 2, -column => 3, );

MainLoop;

# subroutines
sub update_time {
    my $ct = shift @_;
    $ts = sprintf qq{%s}, scalar localtime $ct;
}