Normally, in these types of apps, if you destroy the main window ( eventloop) the script will continue on and you can do what you want. I don't do Wx, but here is a simple Tk version

#!/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;
MainLoop;

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

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

#process your password here and continue with your script
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