perlsyn.pod says:
Truth and Falsehood
The number 0, the strings ’0’ and ’’, the empty list "()", and "undef" are all false in a boolean context. All other values are true. Negation of a true value by "!" or "not" returns a special false value. When evaluated as a string it is treated as ’’, but as a number, it is treated as 0.

In reply to Re^3: printing true false values by tinita
in thread printing true false values by HarshaHegde

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