I get:
Name "Our_package::my_variable" used only once: possible
typo at scope.pl line 41. for

print "4) \$Our_package::my_variable NOT DEFINED\n"
 if not (defined $Our_package::my_variable);
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Shouldn't $Our_package::my_variable be something?
I'm looking for a typo but ...

You're right! I get the warning, too, but I let this happen on purpose. This generates a warning because I purposely refer to a variable declared 'my my_variable' in the other package. Since it's declared with 'my', it is (let's see if I get this right) lexically scoped only to the other package, so the calling program can't see it. As I understand it, a variable with lexical scoping means that it only exists within a particular textual area of code, in this case, the package "Our_package". I guess a solution to this would be for me to change the "#!/usr/bin/perl -w" to "#!/usr/bin/perl". Or maybe print a disclaimer about the warning. The point is, the user should learn from this that a 'my' variable in a package is not visible from outside that package.