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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 particular integer width, especially not to
       the C language "char".  Unicode is language-neutral and
       display-neutral: it does not encode the language of the
       text and it does not generally 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.  Furthermore, various
       operations on the characters like uppercasing,
       lowercasing, 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 modifiers (like "COMBINING



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       ACUTE ACCENT").  This sequence of base character 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", 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 precomposed characters.
       "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 normalization
       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, Unicode 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 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



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       define the characters used by a language 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 somehow.  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 surrogates 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 needed
       only in much more restricted circumstances. In earlier
       releases the "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,
       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 identifier 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.




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       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 ":encoding" or ":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.



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       There, Unicode support is somewhat more complex to
       implement since additional conversions 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



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       string constants: 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
       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 "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.

       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



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       at code points 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, ">: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. Also note that ":utf8" is unsafe for
       input, because it accepts the data without validating that
       it is indeed valid UTF8.

       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 Unicode in Perl's eyes.  To do that,
       specify the appropriate layer when opening files

           open(my $fh,'<:encoding(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 ':encoding(utf8)'; # input/output default encoding will be UTF-8
           open X, ">file";
           print X chr(0x100), "\n";
           close X;
           open Y, "<file";
           printf "%#x\n", ord(<Y>); # this should print 0x100
           close Y;



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       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, "<koi8");
           printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
           close I;

       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 open pragma affects all the "open()" calls after the
       pragma by setting 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 "binmode()"; 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 ":encoding(...)" methods do work
       with all of "open()", "binmode()", and the "open" pragma.

       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(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 allows for flexible names: "koi8-r" and
       "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
       Encode::Supported.

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




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       Notice that because of the default behaviour of not doing
       any 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 the data:

           # BAD CODE WARNING
           open F, "file";
           local $/; ## read in the whole file of 8-bit characters
           $t = <F>;
           close F;
           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 file will
       be twice UTF-8 encoded.  A "use open ':encoding(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 displayed
       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("W*", $_[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()




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           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
           internally-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 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 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 "unpack("C*", ..." to get
           the bytes of whatever the string encoding happens to
           be, or "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("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
           "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 sometimes, any
           CAPITAL LETTER As should be considered equal, or even
           As of any case.




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           The long answer is that you need to consider character
           normalization 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.unicode.org/unicode/reports/tr21/>

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

       o   String Collation

           People like to see their strings nicely sorted--or as
           Unicode parlance 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 characters.  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 is 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



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           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 behaviour 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 LETTER 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 have to care.  But you may, because
           currently the semantics of the characters whose
           ordinals are in the range 128 to 255 is different
           depending on whether the string they are contained
           within is in Unicode or not.  (See perlunicode.)

           To determine if a string is in Unicode, use:

               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 (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,




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               $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 the "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
                                             # (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 (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
                   # $string is valid utf8
               } else {
                   # $string is not valid utf8
               }

           Or use "unpack" to try decoding it:

               use warnings;
               @chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);

           If invalid, a "Malformed UTF-8 character" warning is
           produced. The "C0" means "process the string character
           per character".  Without that, the "unpack("U*", ...)"
           would work in "U0" mode (the default if the format
           string starts with "U") and it would return the bytes
           making up the UTF-8 encoding of the target string,
           something that will always work.

       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.




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           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 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 "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 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("W*", unpack("U*", $Unicode_string));
               $Unicode_string = pack("U*", unpack("W*", $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);

           or:

               $Unicode = pack("U0a*", $bytes);




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           You can find the bytes that make up a UTF-8 sequence
           with

                   @bytes = unpack("C*", $Unicode_string)

           and you can create well-formed Unicode with

                   $Unicode_string = 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 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.  The "U+HHHH" notation uses
       hexadecimal, 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 number in
       decimal, and "printf "%x\n", $decimal" will show a decimal
       number 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




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   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{installprivlib} 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", "Unicode::Map8", and "Unicode::Map",



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       available from CPAN.  If you have the GNU recode
       installed, you can also use the Perl front-end
       "Convert::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
       perlunitut, perlunicode, Encode, open, utf8, bytes,
       perlretut, perlrun, Unicode::Collate, Unicode::Normalize,
       Unicode::UCD

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 mailing lists for their valuable
       feedback.

AUTHOR, COPYRIGHT, AND LICENSE
       Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>

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



























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