If you plan on using that directory as part of a filename, you could always give File::Spec a try. Not only will it do what you want by converting C:/windows to C:\windows, it helps you write portable code.

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

my $dir = 'c:/temp';
my $file = 'tempfile';

my $path = File::Spec->catfile($dir, $file);
print $path, "\n";
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Which will output C:\temp\tempfile