> Is there a perl's built-in way to get a reference of the parent,

No these data structures hold only references (only a "is_child" relation if you want), and like choroba already pointed out many "parents" can have the same "child".

> Or the only ways to do it is iteratively search an entire complex variable or indexing it and searching the index?

Many more possibilities:

• you pass a path ['key_of_arr',3] instead of a sub-ref "somewhere"
• you keep the needed reference to the interesting parents in deeper nested structures. (beware of circular references and the risk of memory leaks then)
• you keep the string "key_of_arr" inside deeper nested structures. (no risk of memory leaks then)

The best strategy depends on the details (which we don't know). Most probably you just need to redesign your data.

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