re File::Copy - ok it is core so fine to use, although I admit I don't look for a module as much as I could because I can only use core modules in production, so i tend to have to reinvent the wheel a lot

re text files - undefining $/ does support text files.

re slurp into memory - the exact behaviour, whether full slurp or buffered (I would expect fixed size buffering to match i/o page size if so) is a bit off-piste here I think.

re error handling. yes of course, but error handling when done properly will be called up from some other project module - also an off-piste topic.

Never heard of "off-piste" before, but if it means irrelevant, you're wrong on both counts.