Well, you could read perldelta, and keep tracks of the reported bugs on perlbug, but that doesn't mean you detect all things that break your programs.

But there are things you can do. First is to have a testing environment, and a solid test suite. This hopefully unearth things that break. But testing only determines breakage, it doesn't resolve them.

A better approach is to have each application (or set of applications) carry its own version of Perl. That is, you package an appropriate run-time environment of perl with your application. Then, if one application needs a newer version of Perl, no other application will break. Installing newer versions of modules won't break other applications. One can easily have different 'types' (64-bit ints, threads, dynamic library) of perl as well this way.

Abigail