This exercise comes from the filehandle reference chapter. You're supposed to open files for each character and write to the correct file when you encounter a line of input. The hint from the end of the exercise is:

Hint: use a hash, keyed by the castaway name, holding IO::File objects for each output file. Create them as necessary.

The hash is for the filehandles, not the data. Give it another go, and if you need more of a hint, peek at the exercise answer. Good luck :)