perluniintro


DESCRIPTION
       This document gives a general idea of Unicode and how to use Unicode in
       Perl.  See "Further Resources" for references to more in-depth
       treatments of Unicode.

   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 unify almost
       all other modern character set standards, covering more than 80 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
       6.0 in October 2010.

       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.  A code point is essentially the position of the character
       within the set of all possible Unicode characters, and thus in Perl,
       the term ordinal is often used interchangeably with it.

       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 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,
       which was later further refined into the extended grapheme cluster.
       For example, a Korean Hangul syllable is considered a single logical

       For some combinations of base character and modifiers, there are
       precomposed characters.  There is a single character equivalent, for
       example, to the sequence "LATIN CAPITAL LETTER A" followed by
       "COMBINING ACUTE ACCENT".  It is called  "LATIN CAPITAL LETTER A WITH
       ACUTE".  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 ISO 8859).
       Using sequences, as Unicode does, allows for needing fewer basic
       building blocks (code points) to express many more potential grapheme
       clusters.  To support conversion between equivalent forms, various
       normalization forms are also defined.  Thus, "LATIN CAPITAL LETTER A
       WITH ACUTE" is in Normalization Form Composed, (abbreviated NFC), and
       the sequence "LATIN CAPITAL LETTER A" followed by "COMBINING ACUTE
       ACCENT" represents the same character in Normalization Form Decomposed
       (NFD).

       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
       not also 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 is "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 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.
       in quotemeta).   To enable this seamless support, you should "use
       feature 'unicode_strings'" (which is automatically selected if you "use
       5.012" or higher).  See feature.  (5.14 also fixes a number of bugs and
       departures from the Unicode standard.)

       Before Perl 5.8.0, the use of "use utf8" 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.
       Starting with Perl 5.8.0, 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 general 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.  Prior to Perl 5.14, the upgrade was not
       completely transparent (see "The "Unicode Bug"" in perlunicode), and
       for backwards compatibility, full transparency is not gained unless
       "use feature 'unicode_strings'" (see feature) or "use 5.012" (or
       higher) is selected.

       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");


       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
       perlbug@perl.org

       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}";


          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 cluster.  (Thus "\X" in a
       regular expression would match the entire sequence of both the example
       characters.)

       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 the legacy data is assumed to be ISO
       8859-1 (or EBCDIC, if applicable).

       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";

       always be specified exactly like that; it is not subject to the loose
       matching of encoding names. Also note that currently ":utf8" is unsafe
       for input, because it accepts the data without validating that it is
       indeed valid UTF-8; you should instead use ":encoding(utf-8)" (with or
       without a hyphen).

       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;

       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.

       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()".

       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

   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 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 A's should be considered equal, or
           even A's of any case.

           The long answer is that you need to consider character
           normalization and casing issues: see Unicode::Normalize, Unicode
           Technical Report #15, Unicode Normalization Forms
           (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 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).  To get safe
           conversions from any Unicode string, use "num()" in Unicode::UCD.

   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
           "When Unicode Does Not Happen" in 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 (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, or printf/sprintf parameter substitution), the
           result will be UTF-8 encoded as if copies of the byte strings were
           upgraded to UTF-8: for example,

               $a = "ab\x80c";
               $b = "\x{100}";
               print "$a = $b\n";

           the output string will be UTF-8-encoded "ab\x80c = \x{100}\n", but
           $a will stay byte-encoded.

           Sometimes you might really need to know the byte length of a string
           instead of the character length. For that use either the
           "Encode::encode_utf8()" function or the "bytes" pragma and 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 Find Out What Encoding a File Has?

           You might try Encode::Guess, but it has a number of limitations.

       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 }) {

           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 "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:

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

       o   How Does Unicode Work With Traditional Locales?

           Perl tries to keep the two separated.  Code points that are above
           255 are treated as Unicode; those below 256, generally as locale.
           This works reasonably well except in some case-insensitive regular
           expression pattern matches that in Unicode would cross the 255/256
           boundary.  These are disallowed.  Also, the "\p{}" and "\N{}"
           constructs silently assume Unicode values even for code points
           below 256.  See also 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

   Further Resources
       o   Unicode Consortium

           <http://www.unicode.org/>

       o   Unicode FAQ

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

           <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   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.

       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 2001-2011 Jarkko Hietaniemi <jhi@iki.fi>

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



perl v5.14.2                      2011-09-26                   PERLUNIINTRO(1)
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