# 1.)
scalar grep defined, values %$hash;

# 2.)
undef $_ for values %$hash;

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At 2.), I interpreted your question as in just emptying all slots, without removing their keys.

Makeshifts last the longest.

In reply to Re: One liner to Check and undef hash elements by Aristotle
in thread One liner to Check and undef hash elements by Anonymous Monk

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