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perluniintro
 
PERLUNIINTRO(1)        Perl Programmers Reference Guide        PERLUNIINTRO(1)



NAME
       perluniintro - Perl Unicode introduction

DESCRIPTION
       This document gives a general idea of Unicode and how to use Unicode in
       Perl.

       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,
       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 character is an abstract entity.  It is not bound to any par-
       ticular integer width, especially not to the C language "char".	Uni-
       code 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 "LATIN CAPITAL LETTER A" or "GREEK
       SMALL LETTER ALPHA" and unique numbers for the characters, in this case
       0x0041 and 0x03B1, respectively.  These unique numbers are called code
       points.

       The Unicode standard prefers using hexadecimal notation for the code
       points.	If numbers like 0x0041 are unfamiliar to you, take a peek at a
       later section, "Hexadecimal Notation".  The Unicode standard uses the
       notation "U+0041 LATIN CAPITAL LETTER A", to give the hexadecimal code
       point and the normative name of the character.

       Unicode also defines various properties for the characters, like
       "uppercase" or "lowercase", "decimal digit", or "punctuation"; these
       properties are independent of the names of the characters.  Further-
       more, various operations on the characters like uppercasing, lowercas-
       ing, and collating (sorting) are defined.

       A Unicode character consists either of a single code point, or a base
       character (like "LATIN CAPITAL LETTER A"), followed by one or more mod-
       ifiers (like "COMBINING ACUTE ACCENT").	This sequence of base charac-
       ter and modifiers is called a combining character sequence.

       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", how-
       ever, 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 determin-
       istic.  In this document, we take that second  point of view: one
       "character" is one Unicode code point, be it a base character or a com-
       bining character.

       For some combinations, there are precomposed characters.  "LATIN CAPI-
       TAL 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 conver-
       sions between Unicode and legacy standards (like the ISO 8859).	In the
       general case, the composing method is more extensible.  To support con-
       version between different compositions of the characters, various nor-
       malization forms to standardize representations are also defined.

       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 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, Uni-
       code is only represented as 0x10000 (or 65536) characters from 0x0000
       to 0xFFFF.  This is untrue.  Since Unicode 2.0 (July 1996), Unicode has
       been defined all the way up to 21 bits (0x10FFFF), and since Unicode
       3.1 (March 2001), characters have been defined beyond 0xFFFF.  The
       first 0x10000 characters are called the Plane 0, or the Basic Multilin-
       gual 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 lan-
       guage or a set of languages.  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 scripts, which is more useful: there is "Latin"
       script, "Greek" script, and so on.  Scripts usually span varied parts
       of several blocks.  For further information see Unicode::UCD.

       The Unicode code points are just abstract numbers.  To input and output
       these abstract numbers, the numbers must be encoded or serialised some-
       how.  Unicode defines several character encoding forms, of which 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 sur-
       rogates and byte order marks (BOMs) are--see perlunicode.

       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
       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.

       Starting from Perl 5.8.0, the use of "use utf8" is no longer necessary.
       In earlier releases the "utf8" pragma was used to declare that opera-
       tions 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 "use utf8" is needed: if your
       Perl script itself is encoded in UTF-8, you can use UTF-8 in your iden-
       tifier names, and in string and regular expression literals, by saying
       "use utf8".  This is not the default because scripts with legacy 8-bit
       data in them would break.  See utf8.

       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 transparently upgraded to
       Unicode.

       Internally, Perl currently uses either whatever the native eight-bit
       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 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 -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:

	    Wide character in print at ...

       To output UTF-8, use the ":utf8" output layer.  Prepending

	     binmode(STDOUT, ":utf8");

       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 "open()" layer, and @ARGV by using either the "-C" command line
       switch or the "PERL_UNICODE" environment variable, see perlrun for the
       documentation of the "-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
       "useperlio=define".

       Unicode and EBCDIC

       Perl 5.8.0 also supports Unicode on EBCDIC platforms.  There, Unicode
       support is somewhat more complex to implement since additional conver-
       sions are needed at every step.	Some problems remain, see 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".

       Creating Unicode

       To create Unicode characters in literals for code points above 0xFF,
       use the "\x{...}" notation in double-quoted strings:

	   my $smiley = "\x{263a}";

       Similarly, it can be used in regular expression literals

	   $smiley =~ /\x{263a}/;

       At run-time you can use "chr()":

	   my $hebrew_alef = chr(0x05d0);

       See "Further Resources" for how to find all these numeric codes.

       Naturally, "ord()" will do the reverse: it turns a character into a
       code point.

       Note that "\x.." (no "{}" and only two hexadecimal digits), "\x{...}",
       and "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 always produced. If
       you want to force the production of Unicode characters regardless of
       the numeric value, use "pack("U", ...)"	instead of "\x..", "\x{...}",
       or "chr()".

       You can also use the "charnames" pragma to 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 "pack()" numbers into Unicode
       characters:

	  my $georgian_an  = pack("U", 0x10a0);

       Note that both "\x{...}" and "\N{...}" are compile-time string con-
       stants: you cannot use variables in them.  if you want similar run-time
       functionality, use "chr()" and "charnames::vianame()".

       If you want to force the result to Unicode characters, use the special
       "U0" prefix.  It consumes no arguments but forces the result to be in
       Unicode characters, instead of bytes.

	  my $chars = pack("U0C*", 0x80, 0x42);

       Likewise, you can force the result to be bytes by using the special
       "C0" prefix.

       Handling Unicode

       Handling Unicode is for the most part transparent: just use the strings
       as usual.  Functions like "index()", "length()", and "substr()" will
       work on the Unicode characters; regular expressions will work on the
       Unicode characters (see perlunicode and perlretut).

       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 "\X" for matching a combining character sequence.

       Life is not quite so transparent, however, when working with legacy
       encodings, I/O, and certain special cases:

       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 "encoding"
       pragma, for example

	   use encoding 'latin2'; # ISO 8859-2

       in which case literals (string or regular expressions), "chr()", and
       "ord()" in your whole script are assumed to produce Unicode characters
       from ISO 8859-2 code points.  Note that the matching for encoding names
       is forgiving: instead of "latin2" you could have said "Latin 2", or
       "iso8859-2", or other variations.  With just

	   use encoding;

       the environment variable "PERL_ENCODING" will be consulted.  If that
       variable isn't set, the encoding pragma will fail.

       The "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

       Unicode I/O

       Normally, writing out Unicode data

	   print FH $some_string_with_unicode, "\n";

       produces raw bytes that Perl happens to use to internally encode the
       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 0x100 or above, you will get a warn-
       ing.  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, ">:utf8", "file";

	   open FH, ">:encoding(ucs2)",      "file";
	   open FH, ">:encoding(UTF-8)",     "file";
	   open FH, ">:encoding(shift_jis)", "file";

       and on already open streams, use "binmode()":

	   binmode(STDOUT, ":utf8");

	   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 ":utf8" layer must
       always be specified exactly like that; it is not subject to the loose
       matching of encoding names.

       See PerlIO for the ":utf8" layer, PerlIO::encoding and Encode::PerlIO
       for the ":encoding()" layer, and Encode::Supported for many encodings
       supported by the "Encode" module.

       Reading in a file that you know happens to be encoded in one of the
       Unicode or legacy encodings does not magically turn the data into Uni-
       code in Perl's eyes.  To do that, specify the appropriate layer when
       opening files

	   open(my $fh,'<:utf8', 'anything');
	   my $line_of_unicode = <$fh>;

	   open(my $fh,'<:encoding(Big5)', 'anything');
	   my $line_of_unicode = <$fh>;

       The I/O layers can also be specified more flexibly with the "open"
       pragma.	See open, or look at the following example.

	   use open ':utf8'; # input and output default layer will be UTF-8
	   open X, ">file";
	   print X chr(0x100), "\n";
	   close X;
	   open Y, "); # this should print 0x100
	   close Y;

       With the "open" pragma you can use the ":locale" layer

	   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");
	   print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
	   close O;
	   open(I, "), "\n"; # this should print 0xc1
	   close I;

       or you can also use the ':encoding(...)' layer

	   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 con-
       verts data from the specified encoding when it is read in from the
       stream.	The result is always Unicode.

       The open pragma affects all the "open()" calls after the pragma by set-
       ting default layers.  If you want to affect only certain streams, use
       explicit layers directly in the "open()" call.

       You can switch encodings on an already opened stream by using "bin-
       mode()"; see "binmode" in perlfunc.

       The ":locale" does not currently (as of Perl 5.8.0) work with "open()"
       and "binmode()", only with the "open" pragma.  The ":utf8" and ":encod-
       ing(...)" methods do work with all of "open()", "binmode()", and the
       "open" pragma.

       Similarly, you may use these I/O layers on output streams to automati-
       cally 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(iso-2022-jp)', 'text.jis');
	   open(my $unicode, '>:utf8',			'text.utf8');
	   while (<$nihongo>) { print $unicode $_ }

       The naming of encodings, both by the "open()" and by the "open" pragma,
       is similar to the "encoding" pragma in that it allows for flexible
       names: "koi8-r" and "KOI8R" will both be understood.

       Common encodings recognized by ISO, MIME, IANA, and various other stan-
       dardisation organisations are recognised; for a more detailed list see
       Encode::Supported.

       "read()" reads characters and returns the number of characters.
       "seek()" and "tell()" operate on byte counts, as do "sysread()" and
       "sysseek()".

       Notice that because of the default behaviour of not doing any conver-
       sion upon input if there is no default layer, it is easy to mistakenly
       write code that keeps on expanding a file by repeatedly encoding the
       data:

	   # BAD CODE WARNING
	   open F, "file";
	   local $/; ## read in the whole file of 8-bit characters
	   $t = ;
	   close F;
	   open F, ">:utf8", "file";
	   print F $t; ## convert to UTF-8 on output
	   close F;

       If you run this code twice, the contents of the file will be twice
       UTF-8 encoded.  A "use open ':utf8'" would have avoided the bug, or
       explicitly opening also the file for input as UTF-8.

       NOTE: the ":utf8" and ":encoding" features work only if your Perl has
       been built with the new PerlIO feature (which is the default on most
       systems).

       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 dis-
       played as "\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("U*", $_[0])); 	  # unpack Unicode characters
	  }

       For example,

	  nice_string("foo\x{100}bar\n")

       returns the string

	  'foo\x{0100}bar\x0A'

       which is ready to be printed.

       Special Cases


       o   Bit Complement Operator ~ And vec()

	   The bit complement operator "~" 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 inter-
	   nally-encoded bit patterns of the Unicode characters, not on the
	   code point values, which is very probably not what you want.

       o   Peeking At Perl's Internal Encoding

	   Normal users of Perl should never care how Perl encodes any partic-
	   ular 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 layers). But if you must, there are two
	   ways of looking behind the scenes.

	   One way of peeking inside the internal encoding of Unicode charac-
	   ters is to use "unpack("C*", ..." to get the bytes or "unpack("H*",
	   ...)"  to display the bytes:

	       # this prints  c4 80  for the UTF-8 bytes 0xc4 0x80
	       print join(" ", unpack("H*", 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 "utf8::is_utf8()" function.

       Advanced Topics


       o   String Equivalence

	   The question of string equivalence turns somewhat complicated in
	   Unicode: what do you mean by "equal"?

	   (Is "LATIN CAPITAL LETTER A WITH ACUTE" equal to "LATIN CAPITAL
	   LETTER A"?)

	   The short answer is that by default Perl compares equivalence
	   ("eq", "ne") based only on code points of the characters.  In the
	   above case, the answer is no (because 0x00C1 != 0x0041).  But some-
	   times, any CAPITAL LETTER As should be considered equal, or even As
	   of any case.

	   The long answer is that you need to consider character normaliza-
	   tion and casing issues: see Unicode::Normalize, Unicode Technical
	   Reports #15 and #21, Unicode Normalization Forms and Case Mappings,
	   http://www.unicode.org/unicode/reports/tr15/ and http://www.uni-
	   code.org/unicode/reports/tr21/

	   As of Perl 5.8.0, the "Full" case-folding of Case Mappings/Special-
	   Casing is implemented.

       o   String Collation

	   People like to see their strings nicely sorted--or as Unicode par-
	   lance goes, collated.  But again, what do you mean by collate?

	   (Does "LATIN CAPITAL LETTER A WITH ACUTE" come before or after
	   "LATIN CAPITAL LETTER A WITH GRAVE"?)

	   The short answer is that by default, Perl compares strings ("lt",
	   "le", "cmp", "ge", "gt") based only on the code points of the char-
	   acters.  In the above case, the answer is "after", since 0x00C1 >
	   0x00C0.

	   The long answer is that "it depends", and a good answer cannot be
	   given without knowing (at the very least) the language context.
	   See Unicode::Collate, and Unicode Collation Algorithm
	   http://www.unicode.org/unicode/reports/tr10/

       Miscellaneous


       o   Character Ranges and Classes

	   Character ranges in regular expression character classes
	   ("/[a-z]/") and in the "tr///" (also known as "y///") operator are
	   not magically Unicode-aware.  What this means that "[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
	   "/[[:alpha:]]/" in that case.

	   For specifying character classes like that in regular expressions,
	   you can use the various Unicode properties--"\pL", or perhaps
	   "\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
	   perlunicode.

       o   String-To-Number Conversions

	   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).

       Questions With Answers


       o   Will My Old Scripts Break?

	   Very probably not.  Unless you are generating Unicode characters
	   somehow, old behaviour should be preserved.	About the only behav-
	   iour that has changed and which could start generating Unicode is
	   the old behaviour of "chr()" where supplying an argument more than
	   255 produced a character modulo 255.  "chr(300)", for example, was
	   equal to "chr(45)" or "-" (in ASCII), now it is LATIN CAPITAL LET-
	   TER I WITH BREVE.

       o   How Do I Make My Scripts Work With Unicode?

	   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.

       o   How Do I Know Whether My String Is In Unicode?

	   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:

	       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 "is_utf8()"
	   does is to return the value of the internal "utf8ness" flag
	   attached to the $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 (dou-
	   ble-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 "ab\x80c = \x{100}\n", but
	   $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
	   "Encode::encode_utf8()" function or the "bytes" pragma and its only
	   defined function "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 also print 2
					     # (the 0xC4 0x80 of the UTF-8)

       o   How Do I Detect Data That's Not Valid In a Particular Encoding?

	   Use the "Encode" package to try converting it.  For example,

	       use Encode 'decode_utf8';
	       if (decode_utf8($string_of_bytes_that_I_think_is_utf8)) {
		   # valid
	       } else {
		   # invalid
	       }

	   For UTF-8 only, you can use:

	       use warnings;
	       @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);

	   If invalid, a "Malformed UTF-8 character (byte 0x##) in unpack"
	   warning is produced. The "U0" means "expect strictly UTF-8 encoded
	   Unicode".  Without that the "unpack("U*", ...)" would accept also
	   data like "chr(0xFF"), similarly to the "pack" as we saw earlier.

       o   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: encod-
	   ings 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 just binary data, now is it?

	   If you have a raw sequence of bytes that you know should be inter-
	   preted via a particular encoding, you can use "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 remains as "system-native 8-bit bytes".

	   You might relate this to a fictional 'Translate' module:

	      use Translate;
	      my $phrase = "Yes";
	      Translate::from_to($phrase, 'english', 'deutsch');
	      ## 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.

	   Back to converting data.  If you have (or want) data in your sys-
	   tem'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));

	   If you have a sequence of bytes you 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);

	   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
	   use "unpack("C*", $string)" for the former, and you can create
	   well-formed Unicode data by "pack("U*", 0xff, ...)".

       o   How Do I Display Unicode?  How Do I Input Unicode?

	   See http://www.alanwood.net/unicode/ and
	   http://www.cl.cam.ac.uk/~mgk25/unicode.html

       o   How Does Unicode Work With Traditional Locales?

	   In Perl, not very well.  Avoid using locales through the "locale"
	   pragma.  Use only one or the other.	But see perlrun for the
	   description of the "-C" switch and its environment counterpart,
	   $ENV{PERL_UNICODE} to see how to enable various Unicode features,
	   for example by using locale settings.

       Hexadecimal Notation

       The Unicode standard prefers using hexadecimal notation because that
       more clearly shows the division of Unicode into blocks of 256 charac-
       ters.  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.  The "U+HHHH" notation uses hexadeci-
       mal, for example.

       The "0x" prefix means a hexadecimal number, the digits are 0-9 and a-f
       (or A-F, case doesn't matter).  Each hexadecimal digit represents four
       bits, or half a byte.  "print 0x..., "\n"" will show a hexadecimal num-
       ber in decimal, and "printf "%x\n", $decimal" will show a decimal num-
       ber in hexadecimal.  If you have just the "hex digits" of a hexadecimal
       number, you can use the "hex()" function.

	   print 0x0009, "\n";	  # 9
	   print 0x000a, "\n";	  # 10
	   print 0x000f, "\n";	  # 15
	   print 0x0010, "\n";	  # 16
	   print 0x0011, "\n";	  # 17
	   print 0x0100, "\n";	  # 256

	   print 0x0041, "\n";	  # 65

	   printf "%x\n",  65;	  # 41
	   printf "%#x\n", 65;	  # 0x41

	   print hex("41"), "\n"; # 65

       Further Resources


       o   Unicode Consortium

	       http://www.unicode.org/

       o   Unicode FAQ

	       http://www.unicode.org/unicode/faq/

       o   Unicode Glossary

	       http://www.unicode.org/glossary/

       o   Unicode Useful Resources

	       http://www.unicode.org/unicode/onlinedat/resources.html

       o   Unicode and Multilingual Support in HTML, Fonts, Web Browsers and
	   Other Applications

	       http://www.alanwood.net/unicode/

       o   UTF-8 and Unicode FAQ for Unix/Linux

	       http://www.cl.cam.ac.uk/~mgk25/unicode.html

       o   Legacy Character Sets

	       http://www.czyborra.com/
	       http://www.eki.ee/letter/

       o   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 lib/unicore was done to
	   avoid naming conflicts with lib/Unicode in case-insensitive
	   filesystems.)  The main Unicode data file is UnicodeData.txt (or
	   Unicode.301 in Perl 5.6.1.)	You can find the $Config{install-
	   privlib} by

	       perl "-V:installprivlib"

	   You can explore various information from the Unicode data files
	   using the "Unicode::UCD" module.

UNICODE IN OLDER PERLS
       If you cannot upgrade your Perl to 5.8.0 or later, you can still do
       some Unicode processing by using the modules "Unicode::String", "Uni-
       code::Map8", and "Unicode::Map", available from CPAN.  If you have the
       GNU recode installed, you can also use the Perl front-end "Con-
       vert::Recode" for character conversions.

       The following are fast conversions from ISO 8859-1 (Latin-1) bytes 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;

	   # UTF-8 to ISO 8859-1
	   s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;

SEE ALSO
       perlunicode, Encode, encoding, open, utf8, bytes, perlretut, perlrun,
       Unicode::Collate, Unicode::Normalize, Unicode::UCD

ACKNOWLEDGMENTS
       Thanks to the kind readers of the perl5-porters@perl.org, perl-uni-
       code@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org mailing
       lists for their valuable feedback.

AUTHOR, COPYRIGHT, AND LICENSE
       Copyright 2001-2002 Jarkko Hietaniemi 

       This document may be distributed under the same terms as Perl itself.



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