# fake_os.pl

BEGIN {
  $^O = 'Unix';
}

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

my $x = File::Spec->catfile('a', 'b', 'c');

print $x;

##</code><code>##

C:\_32\pscrpt\file-spec>perl fake_os.pl
a/b/c
C:\_32\pscrpt\file-spec>perl -MTest::Harness fake_os.pl
a\b\c