The C<use utf8> pragma tells the Perl parser to allow UTF-8 in the
program text in the current lexical scope (allow UTF-EBCDIC on EBCDIC based
-platforms). The C<no utf8> pragma tells Perl to switch back to treating
+platforms). The C<no utf8> pragma tells Perl to switch back to treating
the source text as literal bytes in the current lexical scope.
This pragma is primarily a compatibility device. Perl versions
Bytes in the source text that have their high-bit set will be treated
as being part of a literal UTF-8 character. This includes most
-literals such as identifiers, string constants, constant regular
-expression patterns and package names. On EBCDIC platforms characters
-in the Latin 1 character set are treated as being part of a literal
-UTF-EBCDIC character.
+literals such as identifier names, string constants, and constant
+regular expression patterns.
+
+On EBCDIC platforms characters in the Latin 1 character set are
+treated as being part of a literal UTF-EBCDIC character.
=back
=head2 Utility functions
-The following functions are defined in the C<utf8::> package by the perl core.
+The following functions are defined in the C<utf8::> package by the
+Perl core. You do not need to say C<use utf8> to use these and in fact
+you should not unless you really want to have UTF-8 source code.
=over 4
=item * $num_octets = utf8::upgrade($string);
-Converts internal representation of string to the Perl's internal
-I<UTF-X> form. Returns the number of octets necessary to represent
-the string as I<UTF-X>.
-
-=item * utf8::downgrade($string[, CHECK])
-
-Converts internal representation of string to be un-encoded bytes.
+Converts (in-place) internal representation of string to Perl's
+internal I<UTF-X> form. Returns the number of octets necessary to
+represent the string as I<UTF-X>. Can be used to make sure that the
+UTF-8 flag is on, so that C<\w> or C<lc()> work as expected on strings
+containing characters in the range 0x80-0xFF (oon ASCII and
+derivatives). Note that this should not be used to convert a legacy
+byte encoding to Unicode: use Encode for that. Affected by the
+encoding pragma.
+
+=item * utf8::downgrade($string[, FAIL_OK])
+
+Converts (in-place) internal representation of string to be un-encoded
+bytes. Returns true on success. On failure dies or, if the value of
+FAIL_OK is true, returns false. Can be used to make sure that the
+UTF-8 flag is off, e.g. when you want to make sure that the substr()
+or length() function works with the usually faster byte algorithm.
+Note that this should not be used to convert Unicode back to a legacy
+byte encoding: use Encode for that. B<Not> affected by the encoding
+pragma.
=item * utf8::encode($string)
-Converts (in-place) I<$string> from logical characters to octet sequence
-representing it in Perl's I<UTF-X> encoding.
+Converts (in-place) I<$string> from logical characters to octet
+sequence representing it in Perl's I<UTF-X> encoding. Returns
+nothing. Same as Encode::encode_utf8(). Note that this should not be
+used to convert a legacy byte encoding to Unicode: use Encode for
+that.
=item * $flag = utf8::decode($string)
Attempts to convert I<$string> in-place from Perl's I<UTF-X> encoding
-into logical characters.
+into logical characters. Returns nothing. Same as Encode::decode_utf8().
+Note that this should not be used to convert Unicode back to a legacy
+byte encoding: use Encode for that.
+
+=item * $flag = utf8::is_utf8(STRING)
+
+Test whether STRING is in UTF-8. Same as Encode::is_utf8().
+
+=item * $flag = utf8::valid(STRING)
+
+[INTERNAL] Test whether STRING is in a consistent state regarding
+UTF-8. Will return true is well-formed UTF-8 and has the UTF-8 flag
+on B<or> if string is held as bytes (both these states are 'consistent').
+Main reason for this routine is to allow Perl's testsuite to check
+that operations have left strings in a consistent state. You most
+probably want to use utf8::is_utf8() instead.
=back
-C<utf8::encode> is like C<utf8::upgrade> but the UTF8 flag does not
-get turned on. See L<perlunicode> for more on the UTF8 flag and the C
-API functions C<sv_utf8_upgrade>, C<sv_utf8_downgrade>,
-C<sv_utf8_encode>, C<sv_utf8_decode> that are wrapped by the Perl
-functions C<utf8::upgrade>, C<utf8::downgrade>, C<utf8::encode> and
-C<utf8::decode>.
+C<utf8::encode> is like C<utf8::upgrade>, but the UTF8 flag is
+cleared. See L<perlunicode> for more on the UTF8 flag and the C API
+functions C<sv_utf8_upgrade>, C<sv_utf8_downgrade>, C<sv_utf8_encode>,
+and C<sv_utf8_decode>, which are wrapped by the Perl functions
+C<utf8::upgrade>, C<utf8::downgrade>, C<utf8::encode> and
+C<utf8::decode>. Note that in the Perl 5.8.0 implementation the
+functions utf8::is_utf8, utf8::valid, utf8::encode, utf8::decode,
+utf8::upgrade, and utf8::downgrade are always available, without a
+C<require utf8> statement-- this may change in future releases.
+
+=head1 BUGS
+
+One can have Unicode in identifier names, but not in package/class or
+subroutine names. While some limited functionality towards this does
+exist as of Perl 5.8.0, that is more accidental than designed; use of
+Unicode for the said purposes is unsupported.
+
+One reason of this unfinishedness is its (currently) inherent
+unportability: since both package names and subroutine names may need
+to be mapped to file and directory names, the Unicode capability of
+the filesystem becomes important-- and there unfortunately aren't
+portable answers.
=head1 SEE ALSO
https://perl5.git.perl.org / perl5.git / blobdiff