I installed cygwin and activeperl

Since you have cygwin, you could just run 'ls' in cygwin's bash shell ... and use cygwin's perl (in the same shell) instead of ActivePerl.

But if you want to use ActivePerl, and still be able to run 'ls', then just add C:\cygwin\bin to the end of the path environment variable. (That's assuming you've installed Cygwin into C:\cygwin - otherwise amend accordingly.)

Cheers,
Rob