lc
See the current Perl documentation for lc.
Here is our local, out-dated (pre-5.6) version:
lc - return lower-case version of a string
lc EXPR
lc
Returns an lowercased version of
EXPR. This is the internal function implementing the \L escape in double-quoted strings. Respects current LC_CTYPE locale if use locale in force. See the perllocale manpage.
If
EXPR is omitted, uses $_.