=head1 DESCRIPTION
This document gives a general idea of Unicode and how to use Unicode
-in Perl.
+in Perl. See L</Further Resources> for references to more in-depth
+treatments of Unicode.
=head2 Unicode
Unicode is a character set standard which plans to codify all of the
writing systems of the world, plus many other symbols.
-Unicode and ISO/IEC 10646 are coordinated standards that provide code
-points for characters in almost all modern character set standards,
-covering more than 30 writing systems and hundreds of languages,
+Unicode and ISO/IEC 10646 are coordinated standards that unify
+almost all other modern character set standards,
+covering more than 80 writing systems and hundreds of languages,
including all commercially-important modern languages. All characters
in the largest Chinese, Japanese, and Korean dictionaries are also
encoded. The standards will eventually cover almost all characters in
more than 250 writing systems and thousands of languages.
-Unicode 1.0 was released in October 1991, and 4.0 in April 2003.
+Unicode 1.0 was released in October 1991, and 6.0 in October 2010.
A Unicode I<character> is an abstract entity. It is not bound to any
particular integer width, especially not to the C language C<char>.
Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
SMALL LETTER ALPHA> and unique numbers for the characters, in this
case 0x0041 and 0x03B1, respectively. These unique numbers are called
-I<code points>.
+I<code points>. A code point is essentially the position of the
+character within the set of all possible Unicode characters, and thus in
+Perl, the term I<ordinal> is often used interchangeably with it.
The Unicode standard prefers using hexadecimal notation for the code
points. If numbers like C<0x0041> are unfamiliar to you, take a peek
by one or more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
base character and modifiers is called a I<combining character
sequence>. Some non-western languages require more complicated
-models, so Unicode created the I<grapheme cluster> concept, and then the
-I<extended grapheme cluster>. For example, a Korean Hangul syllable is
-considered a single logical character, but most often consists of three actual
+models, so Unicode created the I<grapheme cluster> concept, which was
+later further refined into the I<extended grapheme cluster>. For
+example, a Korean Hangul syllable is considered a single logical
+character, but most often consists of three actual
Unicode characters: a leading consonant followed by an interior vowel followed
by a trailing consonant.
Whether to call these extended grapheme clusters "characters" depends on your
point of view. If you are a programmer, you probably would tend towards seeing
-each element in the sequences as one unit, or "character". The whole sequence
-could be seen as one "character", however, from the user's point of view, since
-that's probably what it looks like in the context of the user's language.
-
-With this "whole sequence" view of characters, the total number of
-characters is open-ended. But in the programmer's "one unit is one
-character" point of view, the concept of "characters" is more
-deterministic. In this document, we take that second point of view:
-one "character" is one Unicode code point.
-
-For some combinations, there are I<precomposed> characters.
-C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as
-a single code point. These precomposed characters are, however,
-only available for some combinations, and are mainly
-meant to support round-trip conversions between Unicode and legacy
-standards (like the ISO 8859). In the general case, the composing
-method is more extensible. To support conversion between
-different compositions of the characters, various I<normalization
-forms> to standardize representations are also defined.
+each element in the sequences as one unit, or "character". However from
+the user's point of view, the whole sequence could be seen as one
+"character" since that's probably what it looks like in the context of the
+user's language. In this document, we take the programmer's point of
+view: one "character" is one Unicode code point.
+
+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
+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
+conversions between Unicode and legacy standards (like ISO 8859). Using
+sequences, as Unicode does, allows for needing fewer basic building blocks
+(code points) to express many more potential grapheme clusters. To
+support conversion between equivalent forms, various I<normalization
+forms> are also defined. Thus, C<LATIN CAPITAL LETTER A WITH ACUTE> is
+in I<Normalization Form Composed>, (abbreviated NFC), and the sequence
+C<LATIN CAPITAL LETTER A> followed by C<COMBINING ACUTE ACCENT>
+represents the same character in I<Normalization Form Decomposed> (NFD).
Because of backward compatibility with legacy encodings, the "a unique
number for every character" idea breaks down a bit: instead, there is
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 relase 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
=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.
-
-B<Starting from Perl 5.8.0, the use of C<use utf8> is needed only in much more restricted circumstances.> In earlier releases the C<utf8> pragma was used to declare
+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>, 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 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. 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
+operations.
+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
scripts with legacy 8-bit data in them would break. See L<utf8>.
=head2 Perl's Unicode Model
Perl supports both pre-5.6 strings of eight-bit native bytes, and
-strings of Unicode characters. The 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 (mostly) transparently upgraded
-to Unicode. There are some problems--see L<perlunicode/The "Unicode Bug">.
+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 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
+selected.
Internally, Perl currently uses either whatever the native eight-bit
character set of the platform (for example Latin-1) is, defaulting to
the C<-C> command line switch or the C<PERL_UNICODE> environment
variable, see L<perlrun> for the documentation of the C<-C> switch.
-Note that this means that Perl expects other software to work, too:
+Note that this means that Perl expects other software to work the same
+way:
if Perl has been led to believe that STDIN should be UTF-8, but then
-STDIN coming in from another command is not UTF-8, Perl will complain
-about the malformed UTF-8.
+STDIN coming in from another command is not UTF-8, Perl will likely
+complain about the malformed UTF-8.
All features that combine Unicode and I/O also require using the new
PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though:
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.
+have C<\X> for matching an extended grapheme cluster. (Thus C<\X> in a
+regular expression would match the entire sequence of both the example
+characters.)
Life is not quite so transparent, however, when working with legacy
encodings, I/O, and certain special cases:
=head2 Legacy Encodings
-When you combine legacy data and Unicode the legacy data needs
-to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
-applicable) is assumed.
+When you combine legacy data and Unicode, the legacy data needs
+to be upgraded to Unicode. Normally the legacy data is assumed to be
+ISO 8859-1 (or EBCDIC, if applicable).
The C<Encode> module knows about many encodings and has interfaces
for doing conversions between those encodings:
The matching of encoding names is loose: case does not matter, and
many encodings have several aliases. Note that the C<:utf8> layer
must always be specified exactly like that; it is I<not> subject to
-the loose matching of encoding names. Also note that C<:utf8> is unsafe for
+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.
+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.
join("",
map { $_ > 255 ? # if wide character...
sprintf("\\x{%04X}", $_) : # \x{...}
- chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
+ chr($_) =~ /[[:cntrl:]]/ ? # else if control character...
sprintf("\\x%02X", $_) : # \x..
quotemeta(chr($_)) # else quoted or as themselves
} unpack("W*", $_[0])); # unpack Unicode characters
The short answer is that by default Perl compares equivalence (C<eq>,
C<ne>) based only on code points of the characters. In the above
case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
-CAPITAL LETTER As should be considered equal, or even As of any case.
+CAPITAL LETTER A's should be considered equal, or even A's of any case.
The long answer is that you need to consider character normalization
and casing issues: see L<Unicode::Normalize>, Unicode Technical Report #15,
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.
=item *
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).
+To get safe conversions from any Unicode string, use
+L<Unicode::UCD/num()>.
=back
Very little work should be needed since nothing changes until you
generate Unicode data. The most important thing is getting input as
Unicode; for that, see the earlier I/O discussion.
+To get full seamless Unicode support, add
+C<use feature 'unicode_strings'> (or C<use 5.012> or higher) to your
+script.
=item *
How Do I Know Whether My String Is In Unicode?
-You shouldn't have to care. But you may, because currently the semantics of the
-characters whose ordinals are in the range 128 to 255 are different depending on
+You shouldn't have to care. But you may if your Perl is before 5.14.0
+or you haven't specified C<use feature 'unicode_strings'> or C<use
+5.012> (or higher) because otherwise the semantics of the code points
+in the range 128 to 255 are different depending on
whether the string they are contained within is in Unicode or not.
(See L<perlunicode/When Unicode Does Not Happen>.)
are interpreted as the (variable-length, potentially multi-byte) UTF-8 encoded
code points of the characters. Bytes added to a UTF-8 encoded string are
automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars
-are merged (double-quoted interpolation, explicit concatenation, and
+are merged (double-quoted interpolation, explicit concatenation, or
printf/sprintf parameter substitution), the result will be UTF-8 encoded
as if copies of the byte strings were upgraded to UTF-8: for example,
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 C<bytes> pragma and
-the C<length()> function:
+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($unicode)), "\n"; # will print 2
+ print length(Encode::encode_utf8($unicode)),"\n"; # will print 2
use bytes;
print length($unicode), "\n"; # will also print 2
# (the 0xC4 0x80 of the UTF-8)
=item *
+How Do I Find Out What Encoding a File Has?
+
+You might try L<Encode::Guess>, but it has a number of limitations.
+
+=item *
+
How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the C<Encode> package to try converting it.
How Does Unicode Work With Traditional Locales?
-In Perl, not very well. Avoid using locales through the C<locale>
-pragma. Use only one or the other. But see L<perlrun> for the
-description of the C<-C> switch and its environment counterpart,
-C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
-for example by using locale settings.
+Starting in Perl 5.16, you can specify
+
+ use locale ':not_characters';
+
+to get Perl to work well with tradtional locales. 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 specifiy
+C<:not_characters>.
=back
=item *
+Unicode Recommended Reading List
+
+The Unicode Consortium has a list of articles and books, some of which
+give a much more in depth treatment of Unicode:
+L<http://unicode.org/resources/readinglist.html>
+
+=item *
+
Unicode Useful Resources
L<http://www.unicode.org/unicode/onlinedat/resources.html>
=head1 AUTHOR, COPYRIGHT, AND LICENSE
-Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
+Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
This document may be distributed under the same terms as Perl itself.
https://perl5.git.perl.org / perl5.git / blobdiff