For some combinations of base character and modifiers, there are
I<precomposed> characters. There is a single character equivalent, for
-example, to the sequence C<LATIN CAPITAL LETTER A> followed by
+example, for the sequence C<LATIN CAPITAL LETTER A> followed by
C<COMBINING ACUTE ACCENT>. It is called C<LATIN CAPITAL LETTER A WITH
ACUTE>. These precomposed characters are, however, only available for
some combinations, and are mainly meant to support round-trip
otherwise used blocks. Secondly, there are special Unicode control
characters that do not represent true characters.
-A common myth about Unicode is that it is "16-bit", that is,
-Unicode is only represented as C<0x10000> (or 65536) characters from
-C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July
+When Unicode was first conceived, it was thought that all the world's
+characters could be represented using a 16-bit word; that is a maximum of
+C<0x10000> (or 65536) characters from C<0x0000> to C<0xFFFF> would be
+needed. This soon proved to be false, and since Unicode 2.0 (July
1996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>),
-and since Unicode 3.1 (March 2001), characters have been defined
-beyond C<0xFFFF>. The first C<0x10000> characters are called the
-I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode
-3.1, 17 (yes, seventeen) planes in all were defined--but they are
-nowhere near full of defined characters, yet.
-
-Another myth is about Unicode blocks--that they have something to
-do with languages--that each block would define the characters used
-by a language or a set of languages. B<This is also untrue.>
+and Unicode 3.1 (March 2001) defined the first characters above C<0xFFFF>.
+The first C<0x10000> characters are called the I<Plane 0>, or the
+I<Basic Multilingual Plane> (BMP). With Unicode 3.1, 17 (yes,
+seventeen) planes in all were defined--but they are nowhere near full of
+defined characters, yet.
+
+When a new language is being encoded, Unicode generally will choose a
+C<block> of consecutive unallocated code points for its characters. So
+far, the number of code points in these blocks has always been evenly
+divisible by 16. Extras in a block, not currently needed, are left
+unallocated, for future growth. But there have been occasions when
+a later release needed more code points than the available extras, and a
+new block had to allocated somewhere else, not contiguous to the initial
+one, to handle the overflow. Thus, it became apparent early on that
+"block" wasn't an adequate organizing principal, and so the C<Script>
+property was created. (Later an improved script property was added as
+well, the C<Script_Extensions> property.) Those code points that are in
+overflow blocks can still
+have the same script as the original ones. The script concept fits more
+closely with natural language: there is C<Latin> script, C<Greek>
+script, and so on; and there are several artificial scripts, like
+C<Common> for characters that are used in multiple scripts, such as
+mathematical symbols. Scripts usually span varied parts of several
+blocks. For more information about scripts, see L<perlunicode/Scripts>.
The division into blocks exists, but it is almost completely
-accidental--an artifact of how the characters have been and
-still are allocated. Instead, there is a concept called I<scripts>, which is
-more useful: there is C<Latin> script, C<Greek> script, and so on. Scripts
-usually span varied parts of several blocks. For more information about
-scripts, see L<perlunicode/Scripts>.
+accidental--an artifact of how the characters have been and still are
+allocated. (Note that this paragraph has oversimplified things for the
+sake of this being an introduction. Unicode doesn't really encode
+languages, but the writing systems for them--their scripts; and one
+script can be used by many languages. Unicode also encodes things that
+aren't really about languages, such as symbols like C<BAGGAGE CLAIM>.)
The Unicode code points are just abstract numbers. To input and
output these abstract numbers, the numbers must be I<encoded> or
variable length encoding that encodes Unicode characters as 1 to 6
bytes. Other encodings
include UTF-16 and UTF-32 and their big- and little-endian variants
-(UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2
+(UTF-8 is byte-order independent). The ISO/IEC 10646 defines the UCS-2
and UCS-4 encoding forms.
For more information about encodings--for instance, to learn what
=head2 Perl's Unicode Support
-Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode
-natively. Perl 5.8.0, however, is the first recommended release for
+Starting from Perl v5.6.0, Perl has had the capacity to handle Unicode
+natively. Perl v5.8.0, however, is the first recommended release for
serious Unicode work. The maintenance release 5.6.1 fixed many of the
problems of the initial Unicode implementation, but for example
regular expressions still do not work with Unicode in 5.6.1.
-Perl 5.14.0 is the first release where Unicode support is
+Perl v5.14.0 is the first release where Unicode support is
(almost) seamlessly integrable without some gotchas (the exception being
-some differences in L<quotemeta|perlfunc/quotemeta>). To enable this
+some differences in L<quotemeta|perlfunc/quotemeta>, which is fixed
+starting in Perl 5.16.0). To enable this
seamless support, you should C<use feature 'unicode_strings'> (which is
automatically selected if you C<use 5.012> or higher). See L<feature>.
(5.14 also fixes a number of bugs and departures from the Unicode
standard.)
-Before Perl 5.8.0, the use of C<use utf8> was used to declare
+Before Perl v5.8.0, the use of C<use utf8> was used to declare
that operations in the current block or file would be Unicode-aware.
This model was found to be wrong, or at least clumsy: the "Unicodeness"
is now carried with the data, instead of being attached to the
operations.
-Starting with Perl 5.8.0, only one case remains where an explicit C<use
+Starting with Perl v5.8.0, only one case remains where an explicit C<use
utf8> is needed: if your Perl script itself is encoded in UTF-8, you can
use UTF-8 in your identifier names, and in string and regular expression
literals, by saying C<use utf8>. This is not the default because
strings of Unicode characters. The general principle is that Perl tries
to keep its data as eight-bit bytes for as long as possible, but as soon
as Unicodeness cannot be avoided, the data is transparently upgraded
-to Unicode. Prior to Perl 5.14, the upgrade was not completely
+to Unicode. Prior to Perl v5.14.0, the upgrade was not completely
transparent (see L<perlunicode/The "Unicode Bug">), and for backwards
compatibility, full transparency is not gained unless C<use feature
'unicode_strings'> (see L<feature>) or C<use 5.012> (or higher) is
characters regardless of the numeric value, use C<pack("U", ...)>
instead of C<\x..>, C<\x{...}>, or C<chr()>.
-You can also use the C<charnames> pragma to invoke characters
+You can invoke characters
by name in double-quoted strings:
- use charnames ':full';
my $arabic_alef = "\N{ARABIC LETTER ALEF}";
And, as mentioned above, you can also C<pack()> numbers into Unicode
Note that Perl considers grapheme clusters to be separate characters, so for
example
- use charnames ':full';
- print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
+ print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"),
+ "\n";
will print 2, not 1. The only exception is that regular expressions
have C<\X> for matching an extended grapheme cluster. (Thus C<\X> in a
must always be specified exactly like that; it is I<not> subject to
the loose matching of encoding names. Also note that currently C<:utf8> is unsafe for
input, because it accepts the data without validating that it is indeed valid
-UTF8; you should instead use C<:encoding(UTF-8)> (unfortunately this
-specification needs to be in all upper-case with the dash to get the
-safety checking; C<:encoding(utf-8)>, for example, doesn't do the
-checking).
+UTF-8; you should instead use C<:encoding(utf-8)> (with or without a
+hyphen).
See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
L<Encode::PerlIO> for the C<:encoding()> layer, and
You can switch encodings on an already opened stream by using
C<binmode()>; see L<perlfunc/binmode>.
-The C<:locale> does not currently (as of Perl 5.8.0) work with
+The C<:locale> does not currently work with
C<open()> and C<binmode()>, only with the C<open> pragma. The
C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
C<binmode()>, and the C<open> pragma.
bug, or explicitly opening also the F<file> for input as UTF-8.
B<NOTE>: the C<:utf8> and C<:encoding> features work only if your
-Perl has been built with the new PerlIO feature (which is the default
-on most systems).
+Perl has been built with L<PerlIO>, which is the default
+on most systems.
=head2 Displaying Unicode As Text
displayed as C<\x..>, and the rest of the characters as themselves:
sub nice_string {
- join("",
- map { $_ > 255 ? # if wide character...
- sprintf("\\x{%04X}", $_) : # \x{...}
- chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
- sprintf("\\x%02X", $_) : # \x..
- quotemeta(chr($_)) # else quoted or as themselves
- } unpack("W*", $_[0])); # unpack Unicode characters
+ join("",
+ map { $_ > 255 # if wide character...
+ ? sprintf("\\x{%04X}", $_) # \x{...}
+ : chr($_) =~ /[[:cntrl:]]/ # else if control character...
+ ? sprintf("\\x%02X", $_) # \x..
+ : quotemeta(chr($_)) # else quoted or as themselves
+ } unpack("W*", $_[0])); # unpack Unicode characters
}
For example,
sections on case mapping in the L<Unicode Standard|http://www.unicode.org>.
As of Perl 5.8.0, the "Full" case-folding of I<Case
-Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them.
+Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them,
+mostly fixed by 5.14, and essentially entirely by 5.18.
=item *
Unicode does define several other decimal--and numeric--characters
besides the familiar 0 to 9, such as the Arabic and Indic digits.
Perl does not support string-to-number conversion for digits other
-than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
+than ASCII C<0> to C<9> (and ASCII C<a> to C<f> for hexadecimal).
To get safe conversions from any Unicode string, use
L<Unicode::UCD/num()>.
Sometimes you might really need to know the byte length of a string
instead of the character length. For that use either the
-C<Encode::encode_utf8()> function or the (deprecated) C<bytes> pragma
+C<Encode::encode_utf8()> function or the C<bytes> pragma
and the C<length()> function:
my $unicode = chr(0x100);
print length($unicode), "\n"; # will print 1
require Encode;
- print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
- use bytes; # DEPRECATED!
+ print length(Encode::encode_utf8($unicode)),"\n"; # will print 2
+ use bytes;
print length($unicode), "\n"; # will also print 2
# (the 0xC4 0x80 of the UTF-8)
no bytes;
How Do I Find Out What Encoding a File Has?
-Try L<Encode::Guess>.
+You might try L<Encode::Guess>, but it has a number of limitations.
=item *
How Does Unicode Work With Traditional Locales?
-In Perl, not very well. Avoid using locales through the C<locale>
-pragma. Use only one or the other. But see L<perlrun> for the
-description of the C<-C> switch and its environment counterpart,
-C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
-for example by using locale settings.
+If your locale is a UTF-8 locale, starting in Perl v5.20, Perl works
+well for all categories except C<LC_COLLATE> dealing with sorting and
+the C<cmp> operator.
+
+For other locales, starting in Perl 5.16, you can specify
+
+ use locale ':not_characters';
+
+to get Perl to work well with them. The catch is that you
+have to translate from the locale character set to/from Unicode
+yourself. See L</Unicode IE<sol>O> above for how to
+
+ use open ':locale';
+
+to accomplish this, but full details are in L<perllocale/Unicode and
+UTF-8>, including gotchas that happen if you don't specify
+C<:not_characters>.
=back
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