There is no cwd module. The module is named Cwd and is a core module, so it is available with both, Windows and Unix (and likely, every other OS you get a Perl for).

Most likely what trips you up is that Perl on Windows happily loads the file cwd.pm even if the real name is Cwd.pm.

In my experience, writing your scripts on Windows and then using them on Unix works in most parts, asa long as you use forward slashes (/) to separate your directory names and take a look at File::Spec before you do the directory manipulation yourself.