This is a FAQ, found in Perl FAQ 8.

I {changed directory, modified my environment} in a perl
script.  How come the change disappeared when I exited
the script?  How do I get my changes to be visible?

Unix
  In the strictest sense, it can't be done--the script
  executes as a different process from the shell it was
  started from.  Changes to a process are not reflected
  in its parent--only in any children created after the
  change.  There is shell magic that may allow you to
  fake it by eval()ing the script's output in your shell;
  check out the comp.unix.questions FAQ for details.