$ perl -wle '$_ = 1; ($_ |= 9) ^= 4; print'
13
$ perl -wle '$_ = "HI"; ($_ |= "") ^= " " x 2; print'
hi
$ perl -wle 'use feature qw(bitwise); $_ = 1; ($_ |= 9) ^= 4; print'
Can't modify numeric bitwise or (|) in numeric bitwise xor (^) at -e line 1, near "4;"
Execution of -e aborted due to compilation errors.
$ perl -wle 'use feature qw(bitwise); $_ = "HI"; ($_ |.= "") ^.= " " x 2; print'
Can't modify string bitwise or (|.) in string bitwise xor (^.) at -e line 1, near "2;"
Execution of -e aborted due to compilation errors.

$ perl -wle '$_ = 1; ($_ |= 9) ^= 4; print'
13
$ perl -wle '$_ = "HI"; ($_ |= "") ^= " " x 2; print'
hi
$ perl -wle 'use feature qw(bitwise); $_ = 1; ($_ |= 9) ^= 4; print'
13
$ perl -wle 'use feature qw(bitwise); $_ = "HI"; ($_ |.= "") ^.= " " x 2; print'
hi