Any time you call a Tk script for example, your original script will continue to run after the MainLoop is destroyed. So you can just make your own little password popup like this:

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

my $mw = new MainWindow();

my $password = '';

my $entry = $mw->Entry(
  -show=>'*',
  -relief=>'ridge',
  -textvariable=>\$password
)->pack;

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

# when the MainLoop is destroyed, the calling script can continue
MainLoop; 

sub somesub {
    $password = $entry->get;
    print "password ->$password\n";
    $mw->destroy;
 }

print "you can continue on here\n"; 
<>; #wait for keypress to exit;
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