Bzzzt! Crash! This is the sound of the cross-platform compatibility police knocking at your door!

I feel obliged to point out that there is a module that encapsulates the concept of parent directory. Thus your code becomes:

use strict;
use warnings;
use Cwd;
use File::Spec;

print Cwd::realpath(File::Spec->updir);
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When code begins to involve both Cwd and File::Spec, you know it's time to look at Path::Class (see elsewhere in this thread).