=head2 Unicode
-Unicode is a character set standard with plans to cover all of the
+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 the characters in almost all modern character set standards,
+points for characters in almost all modern character set standards,
covering more than 30 writing systems and hundreds of languages,
-including all commercially important modern languages. All characters
+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.
A Unicode I<character> is an abstract entity. It is not bound to any
-particular integer width, and especially not to the C language C<char>.
-Unicode is language neutral and display neutral: it doesn't encode the
-language of the text, and it doesn't define fonts or other graphical
+particular integer width, especially not to the C language C<char>.
+Unicode is language-neutral and display-neutral: it does not encode the
+language of the text and it does not define fonts or other graphical
layout details. Unicode operates on characters and on text built from
those characters.
Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
-SMALL LETTER ALPHA>, and then unique numbers for those, hexadecimal
-0x0041 or 0x03B1 for those particular characters. Such unique
-numbers are called I<code points>.
+SMALL LETTER ALPHA> and unique numbers for the characters, in this
+case 0x0041 and 0x03B1, respectively. These unique numbers are called
+I<code points>.
The Unicode standard prefers using hexadecimal notation for the code
-points. (In case this notation, numbers like 0x0041, is unfamiliar to
-you, take a peek at a later section, L</"Hexadecimal Notation">.)
-The Unicode standard uses the notation C<U+0041 LATIN CAPITAL LETTER A>,
-which gives the hexadecimal code point, and the normative name of
-the character.
+points. If numbers like C<0x0041> are unfamiliar to you, take a peek
+at a later section, L</"Hexadecimal Notation">. The Unicode standard
+uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the
+hexadecimal code point and the normative name of the character.
Unicode also defines various I<properties> for the characters, like
-"uppercase" or "lowercase", "decimal digit", or "punctuation":
+"uppercase" or "lowercase", "decimal digit", or "punctuation";
these properties are independent of the names of the characters.
Furthermore, various operations on the characters like uppercasing,
-lowercasing, and collating (sorting), are defined.
+lowercasing, and collating (sorting) are defined.
A Unicode character consists either of a single code point, or a
I<base character> (like C<LATIN CAPITAL LETTER A>), followed by one or
more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
-a base character and modifiers is called a I<combining character
+base character and modifiers is called a I<combining character
sequence>.
-Whether to call these combining character sequences, as a whole,
-"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, one "character", but from the user viewpoint, the
-sequence as a whole is probably considered one "character", since
-that's probably what it looks like in the context of the user's
-language.
-
-With this "as a whole" view of characters, the 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, and so we
-take that point of view in this document: one "character" is one
-Unicode code point, be it a base character or a combining character.
-
-For some of the combinations there are I<precomposed> characters,
-for example C<LATIN CAPITAL LETTER A WITH ACUTE> is defined as
+Whether to call these combining character sequences "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, be it a base character or
+a combining character.
+
+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,
-often available only for some combinations, and mainly they are
+only available for some combinations, and are mainly
meant to support round-trip conversions between Unicode and legacy
-standards (like the ISO 8859), and in general case the composing
-method is more extensible. To support conversion between the
+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> are also defined.
+forms> to standardize representations are also defined.
Because of backward compatibility with legacy encodings, the "a unique
-number for every character" breaks down a bit: "at least one number
-for every character" is closer to truth. (This happens when the same
-character has been encoded in several legacy encodings.) The converse
-is also not true: not every code point has 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.
+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
+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 would be "16-bit", that is,
-0x10000 (or 65536) characters from 0x0000 to 0xFFFF. B<This is untrue.>
-Since Unicode 2.0 Unicode has been defined all the way up to 21 bits
-(0x10FFFF), and since 3.1 characters have been defined beyond 0xFFFF.
-The first 0x10000 characters are called the I<Plane 0>, or the I<Basic
-Multilingual Plane> (BMP). With the Unicode 3.1, 17 planes in all are
-defined (but nowhere near full of defined characters yet).
-
-Another myth is that the 256-character blocks have something to do
-with languages: a block per language. B<Also this is untrue.>
-The division into the blocks exists but it is almost completely
-accidental, an artifact of how the characters have been historically
-allocated. Instead, there is a concept called I<scripts>, which may
-be more useful: there is C<Latin> script, C<Greek> script, and so on.
-Scripts usually span several parts of several blocks. For further
-information see L<Unicode::UCD>.
+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
+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 that the 256-character blocks 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.>
+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 further information see L<Unicode::UCD>.
The Unicode code points are just abstract numbers. To input and
-output these abstract numbers, the numbers must be I<encoded> 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 bytes (only 4 with the currently
-defined characters). Other encodings include UTF-16 and UTF-32 and their
-big and little endian variants (UTF-8 is byteorder independent).
-The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms.
-
-For more information about encodings, for example to learn what
-I<surrogates> and I<byte order marks> (BOMs) are, see L<perlunicode>.
+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
+bytes (only 4 with the currently defined characters). 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
+and UCS-4 encoding forms.
+
+For more information about encodings--for instance, to learn what
+I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>.
=head2 Perl's Unicode Support
-Starting from Perl 5.6.0, Perl has had the capability of handling
-Unicode natively. The first recommended release for serious Unicode
-work is Perl 5.8.0, however. The maintenance release 5.6.1 fixed many
-of the problems of the initial implementation of Unicode, but for
-example regular expressions didn't really work with Unicode.
+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
+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 no longer
necessary.> In earlier releases the C<utf8> pragma 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, not attached to the operations. (There
-is one remaining case 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
-variable and subroutine names, and in your string and regular
-expression literals, by saying C<use utf8>. This is not the default
-because that would break existing scripts having legacy 8-bit data in
-them.)
+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
+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 the old, pre-5.6, model of 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
-transparently upgraded to Unicode.
+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 transparently upgraded
+to Unicode.
Internally, Perl currently uses either whatever the native eight-bit
-character set of the platform (for example Latin-1) or UTF-8 to encode
-Unicode strings. Specifically, if all code points in the string are
-0xFF or less, Perl uses the native eight-bit character set.
-Otherwise, it uses UTF-8.
-
-A user of Perl does not normally need to know nor care how Perl happens
-to encodes its internal strings, but it becomes relevant when outputting
-Unicode strings to a stream without a discipline (one with the "default
-default"). In such a case, the raw bytes used internally (the native
-character set or UTF-8, as appropriate for each string) will be used,
-and if warnings are turned on, a "Wide character" warning will be issued
-if those strings contain a character beyond 0x00FF.
+character set of the platform (for example Latin-1) is, defaulting to
+UTF-8, to encode Unicode strings. Specifically, if all code points in
+the string are C<0xFF> or less, Perl uses the native eight-bit
+character set. Otherwise, it uses UTF-8.
+
+A user of Perl does not normally need to know nor care how Perl
+happens to encode its internal strings, but it becomes relevant when
+outputting Unicode strings to a stream without a PerlIO layer -- one with
+the "default" encoding. In such a case, the raw bytes used internally
+(the native character set or UTF-8, as appropriate for each string)
+will be used, and a "Wide character" warning will be issued if those
+strings contain a character beyond 0x00FF.
For example,
- perl -w -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
+ perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
produces a fairly useless mixture of native bytes and UTF-8, as well
-as a warning.
+as a warning:
+
+ Wide character in print at ...
-To output UTF-8 always, use the ":utf8" output discipline. Prepending
+To output UTF-8, use the C<:encoding> or C<:utf8> output layer. Prepending
binmode(STDOUT, ":utf8");
-to this sample program ensures the output is completely UTF-8, and
-of course, removes the warning.
+to this sample program ensures that the output is completely UTF-8,
+and removes the program's warning.
+
+You can enable automatic UTF-8-ification of your standard file
+handles, default C<open()> layer, and C<@ARGV> by using either
+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:
+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.
+
+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:
+you can see whether yours is by running "perl -V" and looking for
+C<useperlio=define>.
-Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, the
-support is somewhat harder to implement since additional conversions
-are needed at every step. Because of these difficulties, the Unicode
-support isn't quite as full as in other, mainly ASCII-based, platforms
-(the Unicode support is better than in the 5.6 series, which didn't
-work much at all for EBCDIC platform). 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, UTF-EBCDIC is "EBCDIC-safe").
+=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. Some problems
+remain, see L<perlebcdic> for details.
+
+In any case, the Unicode support on EBCDIC platforms is better than
+in the 5.6 series, which didn't work much at all for EBCDIC platform.
+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".
=head2 Creating Unicode
-To create Unicode characters in literals for code points above 0xFF,
-use the C<\x{...}> notation in doublequoted strings:
+To create Unicode characters in literals for code points above C<0xFF>,
+use the C<\x{...}> notation in double-quoted strings:
my $smiley = "\x{263a}";
-Similarly in regular expression literals
+Similarly, it can be used in regular expression literals
$smiley =~ /\x{263a}/;
my $hebrew_alef = chr(0x05d0);
-(See L</"Further Resources"> for how to find all these numeric codes.)
+See L</"Further Resources"> for how to find all these numeric codes.
-Naturally, C<ord()> will do the reverse: turn a character to a code point.
+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 0x100 (decimal
-256) generate an eight-bit character for backward compatibility with
-older Perls. For arguments of 0x100 or more, Unicode characters are
+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()>.
You can also use the C<charnames> pragma to invoke characters
-by name in doublequoted strings:
+by name in double-quoted strings:
use charnames ':full';
my $arabic_alef = "\N{ARABIC LETTER ALEF}";
constants: you cannot use variables in them. if you want similar
run-time functionality, use C<chr()> and C<charnames::vianame()>.
+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:
+
+ my $chars = pack("U0W*", 0x80, 0x42);
+
+Likewise, you can stop such UTF-8 interpretation by using the special
+C<"C0"> prefix.
+
=head2 Handling Unicode
Handling Unicode is for the most part transparent: just use the
C<substr()> will work on the Unicode characters; regular expressions
will work on the Unicode characters (see L<perlunicode> and L<perlretut>).
-Note that Perl does B<not> consider combining character sequences
-to be characters, such for example
+Note that Perl considers combining character sequences to be
+separate characters, so for example
use charnames ':full';
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 a combining character sequence.
-When life is not quite so transparent is working with legacy
-encodings, and I/O, and certain special cases.
+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. You can override this assumption by
-using the C<encoding> pragma, for example
+applicable) is assumed.
- use encoding 'latin2'; # ISO 8859-2
-
-in which case literals (string or regular expression) and chr/ord
-in your whole script are assumed to produce Unicode characters from
-ISO 8859-2 code points. Note that the matching for the encoding
-names is forgiving: instead of C<latin2> you could have said
-C<Latin 2>, or C<iso8859-2>, and so forth. With just
-
- use encoding;
-
-first the environment variable C<PERL_ENCODING> will be consulted,
-and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed.
-
-The C<Encode> module knows about many encodings and it has interfaces
+The C<Encode> module knows about many encodings and has interfaces
for doing conversions between those encodings:
- use Encode 'from_to';
- from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
+ use Encode 'decode';
+ $data = decode("iso-8859-3", $data); # convert from legacy to utf-8
=head2 Unicode I/O
print FH $some_string_with_unicode, "\n";
produces raw bytes that Perl happens to use to internally encode the
-Unicode string (which depends on the system, as well as what
-characters happen to be in the string at the time). If any of the
-characters are at code points 0x100 or above, you will get a warning
-if you use C<-w> or C<use warnings>. To ensure that the output is
-explicitly rendered in the encoding you desire (and to avoid the
-warning), open the stream with the desired encoding. Some examples:
+Unicode string. Perl's internal encoding depends on the system as
+well as what characters happen to be in the string at the time. If
+any of the characters are at code points C<0x100> or above, you will get
+a warning. To ensure that the output is explicitly rendered in the
+encoding you desire--and to avoid the warning--open the stream with
+the desired encoding. Some examples:
- open FH, ">:ucs2", "file"
- open FH, ">:utf8", "file";
- open FH, ">:Shift-JIS", "file";
+ open FH, ">:utf8", "file";
-and on already open streams use C<binmode()>:
+ open FH, ">:encoding(ucs2)", "file";
+ open FH, ">:encoding(UTF-8)", "file";
+ open FH, ">:encoding(shift_jis)", "file";
+
+and on already open streams, use C<binmode()>:
- binmode(STDOUT, ":ucs2");
binmode(STDOUT, ":utf8");
- binmode(STDOUT, ":Shift-JIS");
-See documentation for the C<Encode> module for many supported encodings.
+ binmode(STDOUT, ":encoding(ucs2)");
+ binmode(STDOUT, ":encoding(UTF-8)");
+ binmode(STDOUT, ":encoding(shift_jis)");
+
+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
+input, because it accepts the data without validating that it is indeed valid
+UTF8.
+
+See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
+L<Encode::PerlIO> for the C<:encoding()> layer, and
+L<Encode::Supported> for many encodings supported by the C<Encode>
+module.
Reading in a file that you know happens to be encoded in one of the
-Unicode encodings does not magically turn the data into Unicode in
-Perl's eyes. To do that, specify the appropriate discipline when
-opening files
+Unicode or legacy encodings does not magically turn the data into
+Unicode in Perl's eyes. To do that, specify the appropriate
+layer when opening files
- open(my $fh,'<:utf8', 'anything');
+ open(my $fh,'<:encoding(utf8)', 'anything');
my $line_of_unicode = <$fh>;
- open(my $fh,'<:Big5', 'anything');
+ open(my $fh,'<:encoding(Big5)', 'anything');
my $line_of_unicode = <$fh>;
-The I/O disciplines can also be specified more flexibly with
-the C<open> pragma; see L<open>:
+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 ':utf8'; # input and output default discipline will be UTF-8
+ use open ':encoding(utf8)'; # input/output default encoding will be UTF-8
open X, ">file";
print X chr(0x100), "\n";
close X;
printf "%#x\n", ord(<Y>); # this should print 0x100
close Y;
-With the C<open> pragma you can use the C<:locale> discipline
+With the C<open> pragma you can use the C<:locale> layer
- $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
+ BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
# the :locale will probe the locale environment variables like LC_ALL
use open OUT => ':locale'; # russki parusski
open(O, ">koi8");
printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
close I;
-or you can also use the C<':encoding(...)'> discipline
-
- open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
- my $line_of_unicode = <$epic>;
-
These methods install a transparent filter on the I/O stream that
converts data from the specified encoding when it is read in from the
stream. The result is always Unicode.
The L<open> pragma affects all the C<open()> calls after the pragma by
-setting default disciplines. If you want to affect only certain
-streams, use explicit disciplines directly in the C<open()> call.
+setting default layers. If you want to affect only certain
+streams, use explicit layers directly in the C<open()> call.
You can switch encodings on an already opened stream by using
C<binmode()>; see L<perlfunc/binmode>.
C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
C<binmode()>, and the C<open> pragma.
-Similarly, you may use these I/O disciplines on output streams to
+Similarly, you may use these I/O layers on output streams to
automatically convert Unicode to the specified encoding when it is
written to the stream. For example, the following snippet copies the
contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
the file "text.utf8", encoded as UTF-8:
- open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
- open(my $unicode, '>:utf8', 'text.utf8');
- while (<$nihongo>) { print $unicode }
+ open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
+ open(my $unicode, '>:utf8', 'text.utf8');
+ while (<$nihongo>) { print $unicode $_ }
The naming of encodings, both by the C<open()> and by the C<open>
-pragma, is similarly understanding as with the C<encoding> pragma:
-C<koi8-r> and C<KOI8R> will both be understood.
+pragma allows for flexible names: C<koi8-r> and C<KOI8R> will both be
+understood.
Common encodings recognized by ISO, MIME, IANA, and various other
standardisation organisations are recognised; for a more detailed
-list see L<Encode>.
+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()>.
Notice that because of the default behaviour of not doing any
-conversion upon input if there is no default discipline,
+conversion upon input if there is no default layer,
it is easy to mistakenly write code that keeps on expanding a file
-by repeatedly encoding:
+by repeatedly encoding the data:
# BAD CODE WARNING
open F, "file";
local $/; ## read in the whole file of 8-bit characters
$t = <F>;
close F;
- open F, ">:utf8", "file";
+ open F, ">:encoding(utf8)", "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 ':utf8'> would have avoided the bug, or
-explicitly opening also the F<file> for input as UTF-8.
+UTF-8 encoded. A C<use open ':encoding(utf8)'> 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. Almost all
-Perl 5.8 platforms do use "perlio", though: you can see whether
-yours is by running "perl -V" and looking for C<useperlio=define>.
+Perl has been built with the new PerlIO feature (which is the default
+on most systems).
=head2 Displaying Unicode As Text
Sometimes you might want to display Perl scalars containing Unicode as
simple ASCII (or EBCDIC) text. The following subroutine converts
its argument so that Unicode characters with code points greater than
-255 are displayed as "\x{...}", control characters (like "\n") are
-displayed as "\x..", and the rest of the characters as themselves:
+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("",
sprintf("\\x{%04X}", $_) : # \x{...}
chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
sprintf("\\x%02X", $_) : # \x..
- chr($_) # else as themselves
- } unpack("U*", $_[0])); # unpack Unicode characters
+ quotemeta(chr($_)) # else quoted or as themselves
+ } unpack("W*", $_[0])); # unpack Unicode characters
}
For example,
nice_string("foo\x{100}bar\n")
-returns:
+returns the string
- "foo\x{0100}bar\x0A"
+ 'foo\x{0100}bar\x0A'
+
+which is ready to be printed.
=head2 Special Cases
Bit Complement Operator ~ And vec()
-The bit complement operator C<~> 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 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.
+The bit complement operator C<~> 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.
=item *
Normal users of Perl should never care how Perl encodes any particular
Unicode string (because the normal ways to get at the contents of a
-string with Unicode -- via input and output -- should always be via
-explicitly-defined I/O disciplines). But if you must, there are two
+string with Unicode--via input and output--should always be via
+explicitly-defined I/O layers). But if you must, there are two
ways of looking behind the scenes.
One way of peeking inside the internal encoding of Unicode characters
-is to use C<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)>
-to display the bytes:
+is to use C<unpack("C*", ...> to get the bytes of whatever the string
+encoding happens to be, or C<unpack("U0..", ...)> to get the bytes of the
+UTF-8 encoding:
# this prints c4 80 for the UTF-8 bytes 0xc4 0x80
- print join(" ", unpack("H*", pack("U", 0x100))), "\n";
+ print join(" ", unpack("U0(H2)*", pack("U", 0x100))), "\n";
Yet another way would be to use the Devel::Peek module:
perl -MDevel::Peek -e 'Dump(chr(0x100))'
-That shows the UTF8 flag in FLAGS and both the UTF-8 bytes
-and Unicode characters in PV. See also later in this document
-the discussion about the C<is_utf8> function of the C<Encode> module.
+That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes
+and Unicode characters in C<PV>. See also later in this document
+the discussion about the C<utf8::is_utf8()> function.
=back
String Equivalence
The question of string equivalence turns somewhat complicated
-in Unicode: what do you mean by equal?
+in Unicode: what do you mean by "equal"?
(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
C<LATIN CAPITAL LETTER A>?)
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 being considered equal, or even any As of any case,
-would be desirable.
+case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any
+CAPITAL LETTER As should be considered equal, or even As of any case.
The long answer is that you need to consider character normalization
-and casing issues: see L<Unicode::Normalize>, and Unicode Technical
+and casing issues: see L<Unicode::Normalize>, Unicode Technical
Reports #15 and #21, I<Unicode Normalization Forms> and I<Case
-Mappings>, http://www.unicode.org/unicode/reports/tr15/
+Mappings>, http://www.unicode.org/unicode/reports/tr15/ and
http://www.unicode.org/unicode/reports/tr21/
-As of Perl 5.8.0, regular expression case-ignoring matching
-implements only 1:1 semantics: one character matches one character.
-In I<Case Mappings> both 1:N and N:1 matches are defined.
+As of Perl 5.8.0, the "Full" case-folding of I<Case
+Mappings/SpecialCasing> is implemented.
=item *
String Collation
-People like to see their strings nicely sorted, or as Unicode
+People like to see their strings nicely sorted--or as Unicode
parlance goes, collated. But again, what do you mean by collate?
(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after
The short answer is that by default, Perl compares strings (C<lt>,
C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the
-characters. In the above case, the answer is "after", since 0x00C1 > 0x00C0.
+characters. In the above case, the answer is "after", since
+C<0x00C1> > C<0x00C0>.
The long answer is that "it depends", and a good answer cannot be
given without knowing (at the very least) the language context.
=item *
-Character Ranges
+Character Ranges and Classes
Character ranges in regular expression character classes (C</[a-z]/>)
and in the C<tr///> (also known as C<y///>) operator are not magically
Unicode-aware. What this means that C<[A-Za-z]> will not magically start
-to mean "all alphabetic letters" (not that it does mean that even for
-8-bit characters, you should be using C</[[:alpha]]/> for that).
+to mean "all alphabetic letters"; not that it does mean that even for
+8-bit characters, you should be using C</[[:alpha:]]/> in that case.
-For specifying things like that in regular expressions, you can use
-the various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>,
-in this particular case. You can use Unicode code points as the end
-points of character ranges, but that means that particular code point
-range, nothing more. For further information, see L<perlunicode>.
+For specifying character classes like that in regular expressions,
+you can use the various Unicode properties--C<\pL>, or perhaps
+C<\p{Alphabetic}>, in this particular case. You can use Unicode
+code points as the end points of character ranges, but there is no
+magic associated with specifying a certain range. For further
+information--there are dozens of Unicode character classes--see
+L<perlunicode>.
=item *
String-To-Number Conversions
-Unicode does define several other decimal (and numeric) characters
-than just the familiar 0 to 9, such as the Arabic and Indic digits.
+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).
=over 4
-=item Will My Old Scripts Break?
+=item *
+
+Will My Old Scripts Break?
Very probably not. Unless you are generating Unicode characters
-somehow, any old behaviour should be preserved. About the only
-behaviour that has changed and which could start generating Unicode
-is the old behaviour of C<chr()> where supplying an argument more
-than 255 produced a character modulo 255 (for example, C<chr(300)>
-was equal to C<chr(45)>).
+somehow, old behaviour should be preserved. About the only behaviour
+that has changed and which could start generating Unicode is the old
+behaviour of C<chr()> where supplying an argument more than 255
+produced a character modulo 255. C<chr(300)>, for example, was equal
+to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH
+BREVE.
+
+=item *
-=item How Do I Make My Scripts Work With Unicode?
+How Do I Make My Scripts Work With Unicode?
Very little work should be needed since nothing changes until you
-somehow generate Unicode data. The greatest trick will be getting
-input as Unicode, and for that see the earlier I/O discussion.
+generate Unicode data. The most important thing is getting input as
+Unicode; for that, see the earlier I/O discussion.
-=item How Do I Know Whether My String Is In Unicode?
+=item *
+
+How Do I Know Whether My String Is In Unicode?
-You shouldn't care. No, you really shouldn't. If you have
-to care (beyond the cases described above), it means that we
+You shouldn't care. No, you really shouldn't. No, really. If you
+have to care--beyond the cases described above--it means that we
didn't get the transparency of Unicode quite right.
Okay, if you insist:
- use Encode 'is_utf8';
- print is_utf8($string) ? 1 : 0, "\n";
+ print utf8::is_utf8($string) ? 1 : 0, "\n";
But note that this doesn't mean that any of the characters in the
string are necessary UTF-8 encoded, or that any of the characters have
code points greater than 0xFF (255) or even 0x80 (128), or that the
string has any characters at all. All the C<is_utf8()> does is to
return the value of the internal "utf8ness" flag attached to the
-$string. If the flag is on, characters added to that string will be
-automatically upgraded to UTF-8 (and even then only if they really
-need to be upgraded, that is, if their code point is greater than 0xFF).
+C<$string>. If the flag is off, the bytes in the scalar are interpreted
+as a single byte encoding. If the flag is on, the bytes in the scalar
+are interpreted as the (multi-byte, variable-length) UTF-8 encoded code
+points of the characters. Bytes added to an 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
+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,
+
+ $a = "ab\x80c";
+ $b = "\x{100}";
+ print "$a = $b\n";
+
+the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but
+C<$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 the C<bytes> pragma
-and its only defined function C<length()>:
+instead of the character length. For that use either the
+C<Encode::encode_utf8()> function or the C<bytes> pragma and its only
+defined function C<length()>:
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 print 2 (the 0xC4 0x80 of the UTF-8)
+ print length($unicode), "\n"; # will also print 2
+ # (the 0xC4 0x80 of the UTF-8)
-=item How Do I Detect Data That's Not Valid In a Particular Encoding
+=item *
+
+How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the C<Encode> package to try converting it.
For example,
- use Encode 'encode_utf8';
- if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
- # valid
+ use Encode 'decode_utf8';
+ eval { decode_utf8($string, Encode::FB_CROAK) };
+ if ($@) {
+ # $string is valid utf8
} else {
- # invalid
+ # $string is not valid utf8
}
-For UTF-8 only, you can use:
+Or use C<unpack> to try decoding it:
use warnings;
- @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
+ @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
-If invalid, a C<Malformed UTF-8 character (byte 0x##) in
-unpack> is produced. The "U0" means "expect strictly UTF-8
-encoded Unicode". Without that the C<unpack("U*", ...)>
-would accept also data like C<chr(0xFF>).
+If invalid, a C<Malformed UTF-8 character> warning is produced. The "C0" means
+"process the string character per character". Without that, the
+C<unpack("U*", ...)> would work in C<U0> mode (the default if the format
+string starts with C<U>) and it would return the bytes making up the UTF-8
+encoding of the target string, something that will always work.
-=item How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
+=item *
+
+How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
This probably isn't as useful as you might think.
Normally, you shouldn't need to.
-In one sense, what you are asking doesn't make much sense: Encodings
-are for characters, and binary data is not "characters", so converting
+In one sense, what you are asking doesn't make much sense: encodings
+are for characters, and binary data are not "characters", so converting
"data" into some encoding isn't meaningful unless you know in what
character set and encoding the binary data is in, in which case it's
-not binary data, now is it?
+not just binary data, now is it?
-If you have a raw sequence of bytes that you know should be interpreted via
-a particular encoding, you can use C<Encode>:
+If you have a raw sequence of bytes that you know should be
+interpreted via a particular encoding, you can use C<Encode>:
use Encode 'from_to';
from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
-The call to from_to() changes the bytes in $data, but nothing material
-about the nature of the string has changed as far as Perl is concerned.
-Both before and after the call, the string $data contains just a bunch of
-8-bit bytes. As far as Perl is concerned, the encoding of the string (as
-Perl sees it) remains as "system-native 8-bit bytes".
+The call to C<from_to()> changes the bytes in C<$data>, but nothing
+material about the nature of the string has changed as far as Perl is
+concerned. Both before and after the call, the string C<$data>
+contains just a bunch of 8-bit bytes. As far as Perl is concerned,
+the encoding of the string remains as "system-native 8-bit bytes".
You might relate this to a fictional 'Translate' module:
## phrase now contains "Ja"
The contents of the string changes, but not the nature of the string.
-Perl doesn't know any more after the call than before that the contents
-of the string indicates the affirmative.
+Perl doesn't know any more after the call than before that the
+contents of the string indicates the affirmative.
-Back to converting data, if you have (or want) data in your system's
+Back to converting data. If you have (or want) data in your system's
native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use
pack/unpack to convert to/from Unicode.
- $native_string = pack("C*", unpack("U*", $Unicode_string));
- $Unicode_string = pack("U*", unpack("C*", $native_string));
+ $native_string = pack("W*", unpack("U*", $Unicode_string));
+ $Unicode_string = pack("U*", unpack("W*", $native_string));
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);
+or:
+
+ $Unicode = pack("U0a*", $bytes);
+
You can convert well-formed UTF-8 to a sequence of bytes, but if
you just want to convert random binary data into UTF-8, you can't.
-Any random collection of bytes isn't well-formed UTF-8. You can
+B<Any random collection of bytes isn't well-formed UTF-8>. You can
use C<unpack("C*", $string)> for the former, and you can create
well-formed Unicode data by C<pack("U*", 0xff, ...)>.
-=item How Do I Display Unicode? How Do I Input Unicode?
+=item *
+
+How Do I Display Unicode? How Do I Input Unicode?
-See http://www.hclrss.demon.co.uk/unicode/ and
+See http://www.alanwood.net/unicode/ and
http://www.cl.cam.ac.uk/~mgk25/unicode.html
-=item How Does Unicode Work With Traditional Locales?
+=item *
+
+How Does Unicode Work With Traditional Locales?
In Perl, not very well. Avoid using locales through the C<locale>
-pragma. Use only one or the other.
+pragma. Use only one or the other. But see L<perlrun> for the
+description of the C<-C> switch and its environment counterpart,
+C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
+for example by using locale settings.
=back
=head2 Hexadecimal Notation
-The Unicode standard prefers using hexadecimal notation because that
-shows better the division of Unicode into blocks of 256 characters.
+The Unicode standard prefers using hexadecimal notation because
+that more clearly shows the division of Unicode into blocks of 256 characters.
Hexadecimal is also simply shorter than decimal. You can use decimal
notation, too, but learning to use hexadecimal just makes life easier
-with the Unicode standard.
+with the Unicode standard. The C<U+HHHH> notation uses hexadecimal,
+for example.
The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and>
a-f (or A-F, case doesn't matter). Each hexadecimal digit represents
four bits, or half a byte. C<print 0x..., "\n"> will show a
hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
show a decimal number in hexadecimal. If you have just the
-"hexdigits" of a hexadecimal number, you can use the C<hex()> function.
+"hex digits" of a hexadecimal number, you can use the C<hex()> function.
print 0x0009, "\n"; # 9
print 0x000a, "\n"; # 10
Unicode Consortium
- http://www.unicode.org/
+http://www.unicode.org/
=item *
Unicode FAQ
- http://www.unicode.org/unicode/faq/
+http://www.unicode.org/unicode/faq/
=item *
Unicode Glossary
- http://www.unicode.org/glossary/
+http://www.unicode.org/glossary/
=item *
Unicode Useful Resources
- http://www.unicode.org/unicode/onlinedat/resources.html
+http://www.unicode.org/unicode/onlinedat/resources.html
=item *
Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
- http://www.hclrss.demon.co.uk/unicode/
+http://www.alanwood.net/unicode/
=item *
UTF-8 and Unicode FAQ for Unix/Linux
- http://www.cl.cam.ac.uk/~mgk25/unicode.html
+http://www.cl.cam.ac.uk/~mgk25/unicode.html
=item *
Legacy Character Sets
- http://www.czyborra.com/
- http://www.eki.ee/letter/
+http://www.czyborra.com/
+http://www.eki.ee/letter/
=item *
$Config{installprivlib}/unicore
-in Perl 5.8.0 or newer, and
+in Perl 5.8.0 or newer, and
$Config{installprivlib}/unicode
in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
-The main Unicode data file is F<Unicode.txt> (or F<Unicode.301> in
+The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
perl "-V:installprivlib"
-Note that some of the files have been renamed from the Unicode
-standard since the Perl installation tries to live by the "8.3"
-filenaming restrictions. The renamings are shown in the
-accompanying F<rename> file.
-
You can explore various information from the Unicode data files using
the C<Unicode::UCD> module.
do some Unicode processing by using the modules C<Unicode::String>,
C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN.
If you have the GNU recode installed, you can also use the
-Perl frontend C<Convert::Recode> for character conversions.
+Perl front-end C<Convert::Recode> for character conversions.
The following are fast conversions from ISO 8859-1 (Latin-1) bytes
-to UTF-8 bytes, the code works even with older Perl 5 versions.
+to UTF-8 bytes and back, the code works even with older Perl 5 versions.
# ISO 8859-1 to UTF-8
s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
=head1 SEE ALSO
-L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<Unicode::Collate>, L<Unicode::Normalize>, L<Unicode::UCD>
+L<perlunitut>, L<perlunicode>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>,
+L<Unicode::UCD>
-=head1 ACKNOWLEDGEMENTS
+=head1 ACKNOWLEDGMENTS
Thanks to the kind readers of the perl5-porters@perl.org,
perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org
=head1 AUTHOR, COPYRIGHT, AND LICENSE
-Copyright 2001 Jarkko Hietaniemi <jhi@iki.fi>
+Copyright 2001-2002 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