MirOS Manual: perluniintro(1)


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 sys-
     tems 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 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 char-
     acters, 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 norma-
     tive name of the character.

     Unicode also defines various properties for the characters,
     like "uppercase" or "lowercase", "decimal digit", or "punc-
     tuation"; these properties are independent of the names of
     the characters. Furthermore, various operations on the char-
     acters like uppercasing, lowercasing, and collating (sort-
     ing) are defined.

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

     Whether to call these combining character sequences "charac-
     ters" depends on your point of view. If you are a program-
     mer, 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 char-
     acter".  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

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     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 char-
     acters 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 charac-
     ters 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 perlun-
     icode.

     Perl's Unicode Support

     Starting from Perl 5.6.0, Perl has had the capacity to han-
     dle Unicode natively.  Perl 5.8.0, however, is the first
     recommended release for serious Unicode work.  The mainte-
     nance release 5.6.1 fixed many of the problems of the ini-
     tial Unicode implementation, but for example regular expres-
     sions 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 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.

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     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.  Other-
     wise, 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.

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     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 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()".

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     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 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
     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 perlun-
     icode 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

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     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 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)");

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     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 Unicode 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, "<file";
         printf "%#x\n", ord(<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, "<koi8");
         printf "%#x\n", ord(<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 converts data from the specified encoding when it is

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     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, 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 standardisation organisations are recognised; for a
     more detailed list see Encode::Supported.

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

     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, ">:utf8", "file";
         print F $t; ## convert to UTF-8 on output
         close F;

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     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 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("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

     +   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 charac-
         ters, but not with much else. So don't do that. Simi-
         larly for "vec()": you will be operating on the
         internally-encoded bit patterns of the Unicode charac-
         ters, not on the code point values, which is very prob-
         ably not what you want.

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     +   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 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

     +   String Equivalence

         The question of string equivalence turns somewhat com-
         plicated 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.

         The long answer is that you need to consider character
         normalization and casing issues: see Unicode::Normalize,
         Unicode Technical Reports #15 and #21, Unicode Normali-
         zation 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.

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     +   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 Col-
         lation Algorithm
         http://www.unicode.org/unicode/reports/tr10/

     Miscellaneous

     +   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.

     +   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).

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     Questions With Answers

     +   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 pro-
         duced 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.

     +   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.

     +   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 charac-
         ters 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 inter-
         preted 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";

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         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)

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

         Use the "Encode" package to try converting it. For exam-
         ple,

             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.

     +   How Do I Convert Binary Data Into a Particular Encoding,
         Or Vice Versa?

         This probably isn't as useful as you might think. Nor-
         mally, you shouldn't need to.

         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 encod-
         ing 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?

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         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 encod-
         ing 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("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 beli-
         ever, 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,
         ...)".

     +   How Do I Display Unicode?  How Do I Input Unicode?

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

     +   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 learn-
     ing 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

     Further Resources

     +   Unicode Consortium

             http://www.unicode.org/

     +   Unicode FAQ

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

     +   Unicode Glossary

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

     +   Unicode Useful Resources

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

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

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

     +   UTF-8 and Unicode FAQ for Unix/Linux

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

     +   Legacy Character Sets

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

     +   The Unicode support files live within the Perl installa-
         tion 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",
     available from CPAN. If you have the GNU recode installed,
     you can also use the Perl front-end "Convert::Recode" for
     character conversions.

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     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-unicode@perl.org, linux-utf8@nl.linux.org, and
     unicore@unicode.org mailing lists for their valuable feed-
     back.

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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