I once write a large, complicated shell/awk/isql program, of
about 2500 lines. I developed it on Solaris, but it had to
run under Windows NT, and HP-UX as well. We had a Unix toolkit
running on Windows, and the entire scripted needed a single
change to run under Windows: the location of the tmp directory. Getting it to run under HP-UX required more changes, most of them due to different switches of tools like
grep.
So, my limited experience says that if you have a good Unix
toolkit, porting shouldn't be much of a problem. Read perlport, and remember that the main difference between Perl
under Unix and Perl under Windows is that the latter doesn't
support everything the former does. Although you might increase your changes if you compile Perl on Windows using
Unix emulation libraries.
Abigail