Here's a full example that makes use of Tk::DialogBox.

use strict;
use warnings;

use Tk;
use Tk::DialogBox;

my $main = MainWindow->new();

my $popup = $main->DialogBox( 
    -title   => "myTitle", 
    -buttons => ["ok", "cancel"] 
);

my $entry = $popup->add("Entry", -width => 40)->pack();

$main->Button( 
    -text    => "Pop!",
    -command => \&pop)->pack();

MainLoop;

###

sub pop {
    my $finished;

    while (!$finished) {    
        my $whichbutton = $popup->Show; 
        if ($whichbutton eq "ok") {
            # do something
            $finished = 1; 
            
            print $entry->get; # you might be interested in this
            
        } elsif ($whichbutton eq "cancel") {
            # do something else
            $finished = 1;

        } else {
            # not finished
        }
    }
}
[download]