You might want (at least to suppress uninitialized warnings, you do use strict and warnings, right?):

# Because of my C++ background
use constant PROJECT => (@ARGV)     ? $ARGV[0] : '';
use constant ARCHIVE => (@ARGV > 1) ? $ARGV[1] : '';
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Hmm, undef should eq '', though with a warning if warnings are enabled. Oh well, the above should fix that also if that's what you're getting.