In general, Windows is sufficiently different from Unix that no single simple rule will cover all of the changes you're going to have to make if you're using system(). If you can find ways to do things in pure Perl, without relying on external commands, that will be much more portable. As others have pointed out, mkdir exists as a Perl builtin. Other things can be done with modules (although getting CPAN working on Windows can be non-trivial, so you may want to constrain yourself to modules that ship with a particular Perl distribution for Windows).