ken@ganymede: ~/tmp
$ perl -Mstrict -Mwarnings -MO=Deparse,-p -E '
> my $message = "Congrats" unless not defined $reward;
> '
Global symbol "$reward" requires explicit package name at -e line 2.
-e had compilation errors.
use warnings;
use strict 'refs';
BEGIN {
    $^H{'feature_unicode'} = q(1);
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
((not defined(${'reward'})) or (my $message = 'Congrats'));
ken@ganymede: ~/tmp
$