You can easily test this yourself. Simply comment out the $msg->send; and insert print statements for $message and $sub.

sub mailme {

    my $message = shift;
    my $sub = shift;

    print "Message = $message\n";
    print "Sub = $sub\n";
}

mailme("this is a message", "this is a subject");

#-OUTPUT-
#Message = this is a message
#Sub = this is a subject
#
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So finally to answer the specific question, yes the shifts should work as intended.