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perluniintro (1)


perluniintro - Perl Unicode introduction


Please see following description for synopsis


Perl Programmers Reference Guide                  PERLUNIINTRO(1)

     perluniintro - Perl Unicode introduction

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

     Unicode is a character set standard which plans to codify
     all of the writing systems of the world, plus many other

     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 logical "character" can actually consist of more
     than one internal actual "character" or code point.  For

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     Western languages, this is adequately modelled by a base
     character (like "LATIN CAPITAL LETTER A") followed by one or
     more modifiers (like "COMBINING ACUTE ACCENT").  This
     sequence of base character and modifiers is called a
     combining character sequence.  Some non-western languages
     require more complicated models, so Unicode created the
     grapheme cluster concept, and then the extended grapheme
     cluster.  For example, a Korean Hangul syllable is
     considered a single logical character, but most often
     consists of three actual Unicode characters: a leading
     consonant followed by an interior vowel followed by a
     trailing consonant.

     Whether to call these extended grapheme clusters
     "characters" depends on your point of view. If you are a
     programmer, you probably would tend towards seeing each
     element in the sequences as one unit, or "character".  The
     whole sequence could be seen as one "character", however,
     from the user's point of view, since that's probably what it
     looks like in the context of the user's language.

     With this "whole sequence" view of characters, the total
     number of characters is open-ended. But in the programmer's
     "one unit is one character" point of view, the concept of
     "characters" is more deterministic.  In this document, we
     take that second point of view: one "character" is one
     Unicode code point.

     For some combinations, there are 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

     A common myth about Unicode is that it is "16-bit", that is,
     Unicode is only represented as 0x10000 (or 65536) characters

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     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 about Unicode blocks--that they have
     something to do with languages--that each block would define
     the characters used by a language or a set of languages.
     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 more
     information about scripts, see "Scripts" in perlunicode.

     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.  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

  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

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     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 (mostly) transparently upgraded to
     Unicode.  There are some problems--see "The "Unicode Bug""
     in perlunicode.

     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.

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     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 conversions are needed at every step.

     Later Perl releases have added code that will not work on
     EBCDIC platforms, and no one has complained, so the
     divergence has continued.  If you want to run Perl on an
     EBCDIC platform, send email to

     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

         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

     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

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     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 constants: you cannot use variables in them.  if you
     want similar run-time functionality, use "chr()" and

     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 grapheme clusters 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 an extended grapheme

     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

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     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 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

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     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;

     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

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     as ISO-2022-JP, aka JIS) to the file "text.utf8", encoded as

         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()".

     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:

         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:

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        sub nice_string {
              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,


     returns the string


     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
         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

             # 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:

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             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()"

  Advanced Topics
     o   String Equivalence

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

         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

         The long answer is that you need to consider character
         normalization and casing issues: see Unicode::Normalize,
         Unicode Technical Report #15, Unicode Normalization
         Forms <> and
         sections on case mapping in the Unicode Standard

         As of Perl 5.8.0, the "Full" case-folding of Case
         Mappings/SpecialCasing is implemented, but bugs remain
         in "qr//i" with them.

     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

         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

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     o   Character Ranges and Classes

         Character ranges in regular expression bracketed
         character classes ( e.g., "/[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;
         for those, if you are using locales (perllocale), use
         "/[[:alpha:]]/"; and if not, use the 8-bit-aware
         property "\p{alpha}").

         All the properties that begin with "\p" (and its inverse
         "\P") are actually character classes that are Unicode-
         aware.  There are dozens of them, see perluniprops.

         You can use Unicode code points as the end points of
         character ranges, and the range will include all Unicode
         code points that lie between those end points.

     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 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

     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?

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         You shouldn't have to care.  But you may, because
         currently the semantics of the characters whose ordinals
         are in the range 128 to 255 are different depending on
         whether the string they are contained within is in
         Unicode or not.  (See "When Unicode Does Not Happen" in

         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 (variable-length, potentially multi-
         byte) UTF-8 encoded code points of the characters.
         Bytes added to a UTF-8 encoded string are automatically
         upgraded to UTF-8.  If mixed non-UTF-8 and UTF-8 scalars
         are merged (double-quoted interpolation, explicit
         concatenation, and printf/sprintf parameter
         substitution), the result will be UTF-8 encoded as if
         copies of the byte strings were upgraded to UTF-8: for

             $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)
             no bytes;

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

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

             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.

         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

             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

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         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);


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

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

                 @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 <> and

     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

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         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

  Further Resources
     o   Unicode Consortium


     o   Unicode FAQ


     o   Unicode Glossary


     o   Unicode Useful Resources


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


     o   UTF-8 and Unicode FAQ for Unix/Linux


     o   Legacy Character Sets

         <> <>

     o   The Unicode support files live within the Perl
         installation in the directory


         in Perl 5.8.0 or newer, and


         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.

     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.

     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

         # UTF-8 to ISO 8859-1

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     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     perlunitut, perlunicode, Encode, open, utf8, bytes,
     perlretut, perlrun, Unicode::Collate, Unicode::Normalize,

     Thanks to the kind readers of the,,, and mailing lists for their valuable

     Copyright 2001-2002 Jarkko Hietaniemi <>

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

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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