Here is a little fancier one for you, with window centering, like a real popup.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $MainWindow = MainWindow->new;
$MainWindow->title("Data Entry Form");

# hide window to prevent a double flicker
# it is raised later after it is built
$MainWindow->withdraw;


$MainWindow->fontCreate('big',
   -family=>'arial',
   -weight=>'bold',
   -size=> 18
   );

my $NameOfPerson; # global variable

$MainWindow -> Label(-justify => 'left',
                     -bg => 'white',
                     -font => 'big',
                     -text => "Name of person : ")
        ->pack(-side => 'left',-anchor => 'n');

my $entry = $MainWindow -> Entry(
             -bg => 'white',
             -font => 'big',
             -selectborderwidth => 10)
            ->pack(-side => 'top',-anchor => 'n');

$entry->bind('<Return>',[\&somesub]);
$entry->focus;


$MainWindow -> Button(-text => "OK",
                     -command => \&somesub)
         ->pack(-side => 'bottom',-anchor => 'center');


#centers window for popup
#CenterWindow($MainWindow, 300, 200);
CenterWindow($MainWindow);

# show window now
$MainWindow->deiconify();
$MainWindow->raise;

MainLoop;

#your script can continue here after Tk is done
# ie after Mainwindow destroy is run
while(1){print time."\t$NameOfPerson Your script continues here\n"; sl
+eep 1;}


sub somesub {
    $,="\n";
    $NameOfPerson = $entry -> get;
    print "\nNameOfPerson ->$NameOfPerson\n";
    $MainWindow -> destroy;
 }

sub CenterWindow {
 my($window, $width, $height) = @_;
 $window->idletasks;
 $width  = $window->reqwidth  unless $width; 
 $height = $window->reqheight unless $height;

 my $x = int(($window->screenwidth  / 2) - ($width  / 2));
 my $y = int(($window->screenheight / 2) - ($height / 2));

 $window->geometry("=${width}x${height}+${x}+${y}");

}
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