#! perl -slw
use strict;
use threads;

our $GUI //= 0;

if( $GUI ) {
    require 'MyGui.pm';
    async( \&MyGui::gui )->detach;
}

while( 1 ) {
    my $in = <STDIN>;
    exit if $in =~ '!bye';
    print $in;
}

__END__
C:\test>MyGui-t
hello
hello

goodbye
goodbye

!bye