Perl one-liner for only printing lines of standard in that are unique

Only print lines if they have never been seen on standard in:

perl -ne 'if (not defined %d) { %d = ();} if (not exists $d{$_}) { $d{$_} = 1; print $_}'

Used like:

printf "hi\nhi\nbye\n" | \
  perl -ne 'if (not defined %d) { %d = ();} if (not exists $d{$_}) { $d{$_} = 1; print $_}'
hi
bye