Of course, in your case, $c is still holding carangaBoomBANG!, so your grep will still find it.

And there are also many other ways in which a value can be copied around, for example, when the memory for the string part of a scalar has to be reallocated in a different region, the old, now unused memory is not cleared in any way.

In short, I don't see much hope for you to erase "sensitive" data from memory within Perl unless you can confine the handling to very short places and control every step of handling.

Personally, I would rely on the security features of the OS, especially that only the superuser (if at all) has read rights to /dev/mem, and no other script is run as the current user which could peek the sensitive data from memory.