You aren't telling us if the directory exists or not. Perl only gives you a helpfull warning, just in case you are trying to stat a file/directory with a newline in it - which would be a common programming error.

If you want to avoid the warning, just use

{ no warnings 'newline';
  next if -d "$dir/$current_filename";
};
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A bare block is a loop construct, so that next won't propagate out. Quick demonstration:

$ perl -le 'for (1..10) { { next if 1 }; print }'
1
2
3
4
5
6
7
8
9
10
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Not sure why the existence of the directory would matter. Most of the time, it doesn't exist.

user@host:/home
# perl -w
print "OK" if -d 'I_swear_this_file_aint_here';
print "See, I told you.\n"
<CTRL+D>
See, I told you.
user@host:/home
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I see no special output if the tested for file doesn't exist. It just silently fails.

But...

Thanks for the warnings info! That looks to be what I need, I'll bet.