> date -u | perl stdin-pipe.pl --opt
$VAR1 = {
          'Initial, opt' => ''
        };

Any option argument will be abandoned; collecting STDIN ...
$VAR1 = {
          ' ...after collecting STDIN, opt' => 'Wed May  3 06:24:29 UTC 2023
'
        };

$VAR1 = {
          'Final, opt' => 'Wed May  3 06:24:29 UTC 2023
'
        };