C:\>perl -MO=Deparse,-p -e" my $foo = shift || die 666;"
(my $foo = (shift(@ARGV) || die(666)));
-e syntax OK

C:\>perl -MO=Deparse,-p -e" my $foo = shift or die 666;"
((my $foo = shift(@ARGV)) or die(666));
-e syntax OK

C:\>perl -e" my $foo = shift || die 666;"
666 at -e line 1.

C:\>perl -e" my $foo = shift or die 666;"
666 at -e line 1.

C:\>