Programming Perl, 4th Edition

fc

fc EXPR
fc

New to v5.16 where it is enabled by use feature "fc", this function returns the full Unicode casefold of EXPR. This is the internal function implementing the \F escape in casefolded strings. Just as titlecase is based on uppercase but different, foldcase is based on lowercase but different. In ASCII there is a one-to-one mapping between only two cases, but in Unicode there is a one-to-many mapping and between three cases. Because that’s too many combinations to check manually each time, a fourth casemap called foldcase was invented as a common intermediary for the other three. It is not a case itself, but it is a casemap.

To compare whether two strings are the same without regard to case, do this:

fc($a) eq fc($b)

Prior to v5.16, the only reliable way to compare strings case-insensitively was with the /i pattern modifier, because Perl has always used casefolding semantics for case-insensitive pattern matches. Knowing this, you can emulate equality comparisons like this:

sub fc_eq($$) {
    my($a, $b) = @_;
    return $a =~ /\A\Q$b\E\z/i;
}

For earlier releases than v5.16, the fc function can be found in the Unicode::CaseFold module on CPAN. For comparisons that are both accent- and case-insensitive, use the eq or cmp methods with a Unicode::Collate collator object that was passed ...