Programming Perl, 4th Edition

uc

uc EXPR
uc

This function returns an uppercased version of EXPR. This is the internal function implementing the \U escape in interpolated strings. For titlecase, use ucfirst instead.

Do not use uc for case-insensitive comparisons the way you may have once done in ASCII, because it gives the wrong answer for Unicode. Instead, use the fc (foldcase) function, either from the CPAN Unicode::CaseFold module or via use feature "fc" in v5.16 or later. See the section A Case of Mistaken Identity in Chapter 6 for more information.

Codepoints in the 128–256 range are ignored by uc if the string does not have Unicode semantics (and locale mode is not in effect), which can be difficult to guess. The unicode_strings feature guarantees Unicode semantics even on those codepoints. See Chapter 6.