My experience is that all the -X file operators work on Windows and FreeBSD. You could try

@files = grep { -s and -f} @files;
[download]

I would make sure that it's actually a file; directories on *ix-ish systems have non-zero size. It would probably also make sense to check to see if you have the required permissions for copying the file into another location, e.g. on *ix, you need write access in the target directory.

Copying files can be done with File::Copy or system,

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...kudos to blazar for his observation about _ and the -X operators.