in reply to Re^2: printing true false values
in thread printing true false values

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.