Quick way of doing it with PerlTk:

use strict ;
use Tk ;

my($mw) = new MainWindow(-title => "Enter Username:") ;

my($str) = "usernam_" ;
my($endSub) = sub { destroy $mw } ;

my($entry) = $mw->Entry(-textvariable => \$str)->pack(-side => 'left',
+ -fill => 'x', -expand => 1) ;
$mw->Button(-text => "Ok", -command => $endSub)->pack(-side => 'left')
+ ;
$mw->Button(-text => "Cancel", -command => sub { exit })->pack(-side =
+> 'left') ;

$entry->focus ;
$entry->icursor('end') ;
$entry->bind('<Return>', $endSub) ;

MainLoop ;

print "result = $str\n" ;
[download]

User can press 'Enter' or the OkButton.