Your mixed case test will not work the way you intended

/[a-zA-Z]/ matches any lower- or uppercase character, not a lower- and then an uppercase one.

And your two substitutions will not flip the case of a character because after the first substitution (i.e. s/([a-z])/\u$1/g) all characters are uppercase and will be changed to lowercase at the second substitution.

In reply to Re^2: Reversing string case by Anonymous Monk
in thread Reversing string case by perlpal

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