If I read you correctly (and it is still early in the morning here), you want caller:

    caller EXPR
    caller  Returns the context of the current subroutine call. In sca
+lar
            context, returns the caller's package name if there is a c
+aller,
            that is, if we're in a subroutine or "eval" or "require", 
+and
            the undefined value otherwise. [....]
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So, unless (defined caller) { ... } will execute that code if it's being brought in as the main level of the program, rather than a module.