=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, 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
+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
"at least one number for every character". The same character could
be represented differently in several legacy encodings. The
-converse is also not true: some code points do not have an assigned
+converse is not true: some code points do not have an assigned
character. Firstly, there are unallocated code points within
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 65,536) characters would be needed, from C<0x0000> to
+C<0xFFFF>. This soon proved to be wrong, 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 principle, 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
I<serialised> somehow. Unicode defines several I<character encoding
-forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a
-variable length encoding that encodes Unicode characters as 1 to 6
+forms>, of which I<UTF-8> is the most popular. UTF-8 is a
+variable length encoding that encodes Unicode characters as 1 to 4
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.
-
-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. (There are a few
+exceptions. Firstly, some differences in L<quotemeta|perlfunc/quotemeta>
+were fixed starting in Perl 5.16.0. Secondly, some differences in
+L<the range operator|perlop/Range Operators> were fixed starting in
+Perl 5.26.0. Thirdly, some differences in L<split|perlfunc/split> were fixed
+started in Perl 5.28.0.)
+
+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:
=head2 Unicode and EBCDIC
-Perl 5.8.0 also supports Unicode on EBCDIC platforms. There,
-Unicode support is somewhat more complex to implement since
-additional conversions are needed at every step.
-
-Later Perl releases have added code that will not work on EBCDIC platforms, and
-no one has complained, so the divergence has continued. If you want to run
-Perl on an EBCDIC platform, send email to perlbug@perl.org
+Perl 5.8.0 added support for Unicode on EBCDIC platforms. This support
+was allowed to lapse in later releases, but was revived in 5.22.
+Unicode support is somewhat more complex to implement since additional
+conversions are needed. See L<perlebcdic> for more information.
On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC
instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in
that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is
-"EBCDIC-safe".
+"EBCDIC-safe", in that all the basic characters (which includes all
+those that have ASCII equivalents (like C<"A">, C<"0">, C<"%">, I<etc.>)
+are the same in both EBCDIC and UTF-EBCDIC. Often, documentation
+will use the term "UTF-8" to mean UTF-EBCDIC as well. This is the case
+in this document.
=head2 Creating Unicode
-To create Unicode characters in literals for code points above C<0xFF>,
-use the C<\x{...}> notation in double-quoted strings:
+This section applies fully to Perls starting with v5.22. Various
+caveats for earlier releases are in the L</Earlier releases caveats>
+subsection below.
- my $smiley = "\x{263a}";
+To create Unicode characters in literals,
+use the C<\N{...}> notation in double-quoted strings:
-Similarly, it can be used in regular expression literals
+ my $smiley_from_name = "\N{WHITE SMILING FACE}";
+ my $smiley_from_code_point = "\N{U+263a}";
- $smiley =~ /\x{263a}/;
+Similarly, they can be used in regular expression literals
-At run-time you can use C<chr()>:
+ $smiley =~ /\N{WHITE SMILING FACE}/;
+ $smiley =~ /\N{U+263a}/;
- my $hebrew_alef = chr(0x05d0);
+At run-time you can use:
-See L</"Further Resources"> for how to find all these numeric codes.
+ use charnames ();
+ my $hebrew_alef_from_name
+ = charnames::string_vianame("HEBREW LETTER ALEF");
+ my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");
Naturally, C<ord()> will do the reverse: it turns a character into
a code point.
-Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
-and C<chr(...)> for arguments less than C<0x100> (decimal 256)
-generate an eight-bit character for backward compatibility with older
-Perls. For arguments of C<0x100> or more, Unicode characters are
-always produced. If you want to force the production of Unicode
-characters regardless of the numeric value, use C<pack("U", ...)>
-instead of C<\x..>, C<\x{...}>, or C<chr()>.
+There are other runtime options as well. You can use C<pack()>:
+
+ my $hebrew_alef_from_code_point = pack("U", 0x05d0);
+
+Or you can use C<chr()>, though it is less convenient in the general
+case:
+
+ $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
+ utf8::upgrade($hebrew_alef_from_code_point);
+
+The C<utf8::unicode_to_native()> and C<utf8::upgrade()> aren't needed if
+the argument is above 0xFF, so the above could have been written as
+
+ $hebrew_alef_from_code_point = chr(0x05d0);
+
+since 0x5d0 is above 255.
+
+C<\x{}> and C<\o{}> can also be used to specify code points at compile
+time in double-quotish strings, but, for backward compatibility with
+older Perls, the same rules apply as with C<chr()> for code points less
+than 256.
-You can also use the C<charnames> pragma to invoke characters
-by name in double-quoted strings:
+C<utf8::unicode_to_native()> is used so that the Perl code is portable
+to EBCDIC platforms. You can omit it if you're I<really> sure no one
+will ever want to use your code on a non-ASCII platform. Starting in
+Perl v5.22, calls to it on ASCII platforms are optimized out, so there's
+no performance penalty at all in adding it. Or you can simply use the
+other constructs that don't require it.
- use charnames ':full';
- my $arabic_alef = "\N{ARABIC LETTER ALEF}";
+See L</"Further Resources"> for how to find all these names and numeric
+codes.
-And, as mentioned above, you can also C<pack()> numbers into Unicode
-characters:
+=head3 Earlier releases caveats
- my $georgian_an = pack("U", 0x10a0);
+On EBCDIC platforms, prior to v5.22, using C<\N{U+...}> doesn't work
+properly.
-Note that both C<\x{...}> and C<\N{...}> are compile-time string
-constants: you cannot use variables in them. if you want similar
-run-time functionality, use C<chr()> and C<charnames::vianame()>.
+Prior to v5.16, using C<\N{...}> with a character name (as opposed to a
+C<U+...> code point) required a S<C<use charnames :full>>.
-If you want to force the result to Unicode characters, use the special
-C<"U0"> prefix. It consumes no arguments but causes the following bytes
-to be interpreted as the UTF-8 encoding of Unicode characters:
+Prior to v5.14, there were some bugs in C<\N{...}> with a character name
+(as opposed to a C<U+...> code point).
- my $chars = pack("U0W*", 0x80, 0x42);
+C<charnames::string_vianame()> was introduced in v5.14. Prior to that,
+C<charnames::vianame()> should work, but only if the argument is of the
+form C<"U+...">. Your best bet there for runtime Unicode by character
+name is probably:
-Likewise, you can stop such UTF-8 interpretation by using the special
-C<"C0"> prefix.
+ use charnames ();
+ my $hebrew_alef_from_name
+ = pack("U", charnames::vianame("HEBREW LETTER ALEF"));
=head2 Handling 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:
use Encode 'decode';
- $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
+ $data = decode("iso-8859-3", $data); # convert from legacy
=head2 Unicode I/O
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
Unicode in Perl's eyes. To do that, specify the appropriate
layer when opening files
- open(my $fh,'<:encoding(utf8)', 'anything');
+ open(my $fh,'<:encoding(UTF-8)', 'anything');
my $line_of_unicode = <$fh>;
open(my $fh,'<:encoding(Big5)', 'anything');
The I/O layers can also be specified more flexibly with
the C<open> pragma. See L<open>, or look at the following example.
- use open ':encoding(utf8)'; # input/output default encoding will be UTF-8
+ use open ':encoding(UTF-8)'; # input/output default encoding will be
+ # UTF-8
open X, ">file";
print X chr(0x100), "\n";
close X;
With the C<open> pragma you can use the C<:locale> layer
BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
- # the :locale will probe the locale environment variables like LC_ALL
+ # the :locale will probe the locale environment variables like
+ # LC_ALL
use open OUT => ':locale'; # russki parusski
open(O, ">koi8");
print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
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.
list see L<Encode::Supported>.
C<read()> reads characters and returns the number of characters.
-C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
-and C<sysseek()>.
+C<seek()> and C<tell()> operate on byte counts, as does C<sysseek()>.
+
+C<sysread()> and C<syswrite()> should not be used on file handles with
+character encoding layers, they behave badly, and that behaviour has
+been deprecated since perl 5.24.
Notice that because of the default behaviour of not doing any
conversion upon input if there is no default layer,
local $/; ## read in the whole file of 8-bit characters
$t = <F>;
close F;
- open F, ">:encoding(utf8)", "file";
+ open F, ">:encoding(UTF-8)", "file";
print F $t; ## convert to UTF-8 on output
close F;
If you run this code twice, the contents of the F<file> will be twice
-UTF-8 encoded. A C<use open ':encoding(utf8)'> would have avoided the
+UTF-8 encoded. A C<use open ':encoding(UTF-8)'> would have avoided the
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
255 are displayed as C<\x{...}>, control characters (like C<\n>) are
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
+ 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
}
For example,
which is ready to be printed.
+(C<\\x{}> is used here instead of C<\\N{}>, since it's most likely that
+you want to see what the native values are.)
+
=head2 Special Cases
=over 4
=item *
-Bit Complement Operator ~ And vec()
+Starting in Perl 5.28, it is illegal for bit operators, like C<~>, to
+operate on strings containing code points above 255.
-The bit complement operator C<~> may produce surprising results if
+=item *
+
+The vec() function may produce surprising results if
used on strings containing characters with ordinal values above
255. In such a case, the results are consistent with the internal
encoding of the characters, but not with much else. So don't do
-that. Similarly for C<vec()>: you will be operating on the
-internally-encoded bit patterns of the Unicode characters, not on
-the code point values, which is very probably not what you want.
+that, and starting in Perl 5.28, a deprecation message is issued if you
+do so, becoming illegal in Perl 5.32.
=item *
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, and essentially entirely by 5.18.
=item *
character classes that are Unicode-aware. There are dozens of them, see
L<perluniprops>.
-You can use Unicode code points as the end points of character ranges, and the
-range will include all Unicode code points that lie between those end points.
+Starting in v5.22, you can use Unicode code points as the end points of
+regular expression pattern character ranges, and the range will include
+all Unicode code points that lie between those end points, inclusive.
+
+ qr/ [ \N{U+03} - \N{U+20} ] /xx
+
+includes the code points
+C<\N{U+03}>, C<\N{U+04}>, ..., C<\N{U+20}>.
+
+This also works for ranges in C<tr///> starting in Perl v5.24.
=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()>.
=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 rules for 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,
C<$a> will stay byte-encoded.
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:
+instead of the character length. For that use 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($unicode)), "\n"; # will print 2
use bytes;
- print length($unicode), "\n"; # will also print 2
+ print length($unicode), "\n"; # will print 2
# (the 0xC4 0x80 of the UTF-8)
no bytes;
=item *
+How Do I Find Out What Encoding a File Has?
+
+You might try L<Encode::Guess>, but it has a number of limitations.
+
+=item *
+
How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the C<Encode> package to try converting it.
For example,
- use Encode 'decode_utf8';
+ use Encode 'decode';
- if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
- # $string is valid utf8
+ if (eval { decode('UTF-8', $string, Encode::FB_CROAK); 1 }) {
+ # $string is valid UTF-8
} else {
- # $string is not valid utf8
+ # $string is not valid UTF-8
}
Or use C<unpack> to try decoding it:
interpreted via a particular encoding, you can use C<Encode>:
use Encode 'from_to';
- from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
+ from_to($data, "iso-8859-1", "UTF-8"); # from latin-1 to UTF-8
The call to C<from_to()> changes the bytes in C<$data>, but nothing
material about the nature of the string has changed as far as Perl is
If you have a sequence of bytes you B<know> is valid UTF-8,
but Perl doesn't know it yet, you can make Perl a believer, too:
- use Encode 'decode_utf8';
- $Unicode = decode_utf8($bytes);
+ $Unicode = $bytes;
+ utf8::decode($Unicode);
or:
You can find the bytes that make up a UTF-8 sequence with
- @bytes = unpack("C*", $Unicode_string)
+ @bytes = unpack("C*", $Unicode_string)
and you can create well-formed Unicode with
- $Unicode_string = pack("U*", 0xff, ...)
+ $Unicode_string = pack("U*", 0xff, ...)
=item *
How Does Unicode Work With Traditional Locales?
-In Perl, not very well. Avoid using locales through the C<locale>
-pragma. Use only one or the other. But see L<perlrun> for the
-description of the C<-C> switch and its environment counterpart,
-C<$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 v5.26, Perl works
+well for all categories; before this, starting with Perl v5.20, it works
+for all categories but C<LC_COLLATE>, which deals with
+sorting and the C<cmp> operator. But note that the standard
+C<L<Unicode::Collate>> and C<L<Unicode::Collate::Locale>> modules offer
+much more powerful solutions to collation issues, and work on earlier
+releases.
+
+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
=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>
=item *
-The Unicode support files live within the Perl installation in the
-directory
-
- $Config{installprivlib}/unicore
-
-in Perl 5.8.0 or newer, and
-
- $Config{installprivlib}/unicode
-
-in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
-avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
-The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
-Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
-
- perl "-V:installprivlib"
-
You can explore various information from the Unicode data files using
the C<Unicode::UCD> module.
=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>.
+Now maintained by Perl 5 Porters.
This document may be distributed under the same terms as Perl itself.
https://perl5.git.perl.org / perl5.git / blobdiff