IomSpace:

If the lines are truly duplicates, and you don't care about the ordering, then I think I'd leverage the sort utility to remove duplicates and just open^[1] the file with:

open(my $in, '-|', "sort -u /Users/mydir/Desktop/CCDS.current.txt") or
+ die " Can't open file: $!";
[download]

Then your code can be considerably shorter/simpler.

Note: [1] From my reading, I think this is how to use an input pipe with the three-argument form of open, but I've not used it before.

...roboticus

When your only tool is a hammer, all problems look like your thumb.