# after the program name
perl -s -e "print join ' ', $0, $R"  -R=OK
Unrecognized switch: -R=OK  (-h will show valid options).

# before an argument of --
perl -s -e "print join ' ', $0, $R"  -R=OK --
Unrecognized switch: -R=OK  (-h will show valid options).

# it works in the opposite way of what perlrun states
perl -s -e "print join ' ', $0, $R" -- -R=OK
-e OK