perl-doc 5.22.1-9ubuntu0.6 / usr / share / perl / 5.22.1 / utf8.pod

=head1 NAME

utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code

=head1 SYNOPSIS

 use utf8;
 no utf8;

 # Convert the internal representation of a Perl scalar to/from UTF-8.

 $num_octets = utf8::upgrade($string);
 $success    = utf8::downgrade($string[, $fail_ok]);

 # Change each character of a Perl scalar to/from a series of
 # characters that represent the UTF-8 bytes of each original character.

 utf8::encode($string);  # "\x{100}"  becomes "\xc4\x80"
 utf8::decode($string);  # "\xc4\x80" becomes "\x{100}"

 # Convert a code point from the platform native character set to
 # Unicode, and vice-versa.
 $unicode = utf8::native_to_unicode(ord('A')); # returns 65 on both
                                               # ASCII and EBCDIC
                                               # platforms
 $native = utf8::unicode_to_native(65);       # returns 65 on ASCII
                                              # platforms; 193 on EBCDIC

 $flag = utf8::is_utf8($string); # since Perl 5.8.1
 $flag = utf8::valid($string);

=head1 DESCRIPTION

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
the source text as literal bytes in the current lexical scope.

B<Do not use this pragma for anything else than telling Perl that your
script is written in UTF-8.> The utility functions described below are
directly usable without C<use utf8;>.

Because it is not possible to reliably tell UTF-8 from native 8 bit
encodings, you need either a Byte Order Mark at the beginning of your
source code, or C<use utf8;>, to instruct perl.

When UTF-8 becomes the standard source format, this pragma will
effectively become a no-op.  For convenience in what follows the term
I<UTF-X> is used to refer to UTF-8 on ASCII and ISO Latin based
platforms and UTF-EBCDIC on EBCDIC based platforms.

See also the effects of the C<-C> switch and its cousin, the
C<PERL_UNICODE> environment variable, in L<perlrun>.

Enabling the C<utf8> pragma has the following effect:

=over 4

=item *

Bytes in the source text that have their high-bit set will be treated
as being part of a literal UTF-X sequence.  This includes most
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

Note that if you have bytes with the eighth bit on in your script
(for example embedded Latin-1 in your string literals), C<use utf8>
will be unhappy since the bytes are most probably not well-formed
UTF-X.  If you want to have such bytes under C<use utf8>, you can disable
this pragma until the end the block (or file, if at top level) by
C<no utf8;>.

=head2 Utility functions

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 say that unless you really want to have UTF-8 source code.

=over 4

=item * C<$num_octets = utf8::upgrade($string)>

Converts in-place the internal representation of the string from an octet
sequence in the native encoding (Latin-1 or EBCDIC) to I<UTF-X>. The
logical character sequence itself is unchanged.  If I<$string> is already
stored as I<UTF-X>, then this is a no-op. 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 Unicode on strings containing characters in the range 0x80-0xFF
(on ASCII and derivatives).

B<Note that this function does not handle arbitrary encodings.>
Therefore Encode is recommended for the general purposes; see also
L<Encode>.

=item * C<$success = utf8::downgrade($string[, $fail_ok])>

Converts in-place the internal representation of the string from
I<UTF-X> to the equivalent octet sequence in the native encoding (Latin-1
or EBCDIC). The logical character sequence itself is unchanged. If
I<$string> is already stored as native 8 bit, then this is a no-op.  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.

Fails if the original I<UTF-X> sequence cannot be represented in the
native 8 bit encoding. On failure dies or, if the value of I<$fail_ok> is
true, returns false. 

Returns true on success.

B<Note that this function does not handle arbitrary encodings.>
Therefore Encode is recommended for the general purposes; see also
L<Encode>.

=item * C<utf8::encode($string)>

Converts in-place the character sequence to the corresponding octet
sequence in I<UTF-X>. That is, every (possibly wide) character gets
replaced with a sequence of one or more characters that represent the
individual I<UTF-X> bytes of the character.  The UTF8 flag is turned off.
Returns nothing.

 my $a = "\x{100}"; # $a contains one character, with ord 0x100
 utf8::encode($a);  # $a contains two characters, with ords (on
                    # ASCII platforms) 0xc4 and 0x80

B<Note that this function does not handle arbitrary encodings.>
Therefore Encode is recommended for the general purposes; see also
L<Encode>.

=item * C<$success = utf8::decode($string)>

Attempts to convert in-place the octet sequence encoded as I<UTF-X> to the
corresponding character sequence. That is, it replaces each sequence of
characters in the string whose ords represent a valid UTF-X byte
sequence, with the corresponding single character.  The UTF-8 flag is
turned on only if the source string contains multiple-byte I<UTF-X>
characters.  If I<$string> is invalid as I<UTF-X>, returns false;
otherwise returns true.

 my $a = "\xc4\x80"; # $a contains two characters, with ords
                     # 0xc4 and 0x80
 utf8::decode($a);   # On ASCII platforms, $a contains one char,
                     # with ord 0x100.   On EBCDIC platforms, $a
                     # is unchanged and the function returns FALSE.

(C<"\xc4\x80"> is not a valid sequence of bytes in any UTF-8-encoded
character(s) in the EBCDIC code pages that Perl supports, which is why the
above example returns failure on them.  What does decode into C<\x{100}>
depends on the platform.  It is C<"\x8C\x41"> in IBM-1047.)

B<Note that this function does not handle arbitrary encodings.>
Therefore Encode is recommended for the general purposes; see also
L<Encode>.

=item * C<$unicode = utf8::native_to_unicode($code_point)>

(Since Perl v5.8.0)
This takes an unsigned integer (which represents the ordinal number of a
character (or a code point) on the platform the program is being run on) and
returns its Unicode equivalent value.  Since ASCII platforms natively use the
Unicode code points, this function returns its input on them.  On EBCDIC
platforms it converts from EBCDIC to Unicode.

A meaningless value will currently be returned if the input is not an unsigned
integer.

Since Perl v5.22.0, calls to this function are optimized out on ASCII
platforms, so there is no performance hit in using it there.

=item * C<$native = utf8::unicode_to_native($code_point)>

(Since Perl v5.8.0)
This is the inverse of C<utf8::native_to_unicode()>, converting the other
direction.  Again, on ASCII platforms, this returns its input, but on EBCDIC
platforms it will find the native platform code point, given any Unicode one.

A meaningless value will currently be returned if the input is not an unsigned
integer.

Since Perl v5.22.0, calls to this function are optimized out on ASCII
platforms, so there is no performance hit in using it there.

=item * C<$flag = utf8::is_utf8($string)>

(Since Perl 5.8.1)  Test whether I<$string> is marked internally as encoded in
UTF-8.  Functionally the same as Encode::is_utf8().

=item * C<$flag = utf8::valid($string)>

[INTERNAL] Test whether I<$string> is in a consistent state regarding
UTF-8.  Will return true if it is well-formed UTF-8 and has the UTF-8 flag
on B<or> if I<$string> is held as bytes (both these states are 'consistent').
Main reason for this routine is to allow Perl's test suite 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 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>.  Also, the functions utf8::is_utf8, utf8::valid,
utf8::encode, utf8::decode, utf8::upgrade, and utf8::downgrade are
actually internal, and thus always available, without a C<require utf8>
statement.

=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

L<perlunitut>, L<perluniintro>, L<perlrun>, L<bytes>, L<perlunicode>

=cut