Just as an adjunct to what you have there, length returns FALSE for a zero-length EXPR and also an undefined EXPR. The latter behaviour was introduced in 5.12.0 (perl5120delta: Other potentially incompatible changes).

Interestingly, given the general discussion here, the FALSE value returned for a zero-length EXPR is 0, while the FALSE value returned for an undefined EXPR is undef.

— Ken

In reply to Re^2: methods for dealing with zero '0' as a string or char by kcott
in thread methods for dealing with zero '0' as a string or char by boleary

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