Programming Perl, 4th Edition

lc

lc EXPR
lc

This function returns a lowercased version of EXPR. This is the internal function implementing the \L escape in double-quoted strings.

Do not use lc 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 lc 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.

Your current LC_CTYPE locale is respected if use locale is in effect, though how locales interact with Unicode is still a topic of ongoing research, as they say. See the perllocale, perlunicode, and perlfunc manpages for the most recent results.