use File::Spec;
use Cwd qw(cwd);

my $dir = cwd;
my $f = File::Spec->catfile($dir, 'admin', 'project.txt');

print "$f\n";                           # ...\admin\project.txt on Windows
print "$f\n";                           # .../admin/project.txt on Linux
use File::Spec::Functions;

my $f = catfile($dir, 'admin', 'project.txt');