Returns the casefolded version of EXPR. This is the internal function
escape in double-quoted strings.
Casefolding is the process of mapping strings to a form where case differences are erased; comparing two strings in their casefolded form is effectively a way of asking if two strings are equal, regardless of case.
Roughly, if you ever found yourself writing this
Now you can write
- fc($this) eq fc($that)
And get the correct results.
Perl only implements the full form of casefolding, but you can access
the simple folds using casefold() in Unicode::UCD and
prop_invmap() in Unicode::UCD.
For further information on casefolding, refer to
the Unicode Standard, specifically sections 3.13
Default Case Operations
, and 5.18
available at http://www.unicode.org/versions/latest/, as well as the
Case Charts available at http://www.unicode.org/charts/case/.
If EXPR is omitted, uses $_ .
This function behaves the same way under various pragmas, such as within
use feature 'unicode_strings ,
as lc does, with the single exception of
fc of LATIN CAPITAL LETTER SHARP S (U+1E9E) within the
scope of use locale . The foldcase of this character
would normally be
, but as explained in the lc
changes that cross the 255/256 boundary are problematic under locales,
and are hence prohibited. Therefore, this function under locale returns
instead the string
, which is the LATIN SMALL LETTER
LONG S. Since that character itself folds to
, the string of two
of them together should be equivalent to a single U+1E9E when foldcased.
While the Unicode Standard defines two additional forms of casefolding, one for Turkic languages and one that never maps one character into multiple characters, these are not provided by the Perl core. However, the CPAN module Unicode::Casing may be used to provide an implementation.