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




NAME

       perluniintro - Perl Unicode introduction


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
       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".  However from the user's point of view, the whole sequence
       could be seen as one "character" since that's probably what it looks
       like in the context of the user's language.  In this document, we take
       the programmer's point of view: one "character" is one Unicode code
       point.

       For some combinations of base character and modifiers, there are
       precomposed characters.  There is a single character equivalent, for
       example, for 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 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.

       When Unicode was first conceived, it was thought that all the world's
       characters could be represented using a 16-bit word; that is a maximum
       of 0x10000 (or 65,536) characters would be needed, from 0x0000 to
       0xFFFF.  This soon proved to be wrong, and since Unicode 2.0 (July
       1996), Unicode has been defined all the way up to 21 bits (0x10FFFF),
       and Unicode 3.1 (March 2001) defined the first characters above 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.

       When a new language is being encoded, Unicode generally will choose a
       "block" of consecutive unallocated code points for its characters.  So
       far, the number of code points in these blocks has always been evenly
       divisible by 16.  Extras in a block, not currently needed, are left
       unallocated, for future growth.  But there have been occasions when a
       later release needed more code points than the available extras, and a
       new block had to allocated somewhere else, not contiguous to the
       initial one, to handle the overflow.  Thus, it became apparent early on
       that "block" wasn't an adequate organizing principal, and so the
       "Script" property was created.  (Later an improved script property was
       added as well, the "Script_Extensions" property.)  Those code points
       that are in overflow blocks can still have the same script as the
       original ones.  The script concept fits more closely with natural
       language: there is "Latin" script, "Greek" script, and so on; and there
       are several artificial scripts, like "Common" for characters that are
       used in multiple scripts, such as mathematical symbols.  Scripts
       usually span varied parts of several blocks.  For more information
       about scripts, see "Scripts" in perlunicode.  The division into blocks
       exists, but it is almost completely accidental--an artifact of how the
       characters have been and still are allocated.  (Note that this
       paragraph has oversimplified things for the sake of this being an
       introduction.  Unicode doesn't really encode languages, but the writing
       systems for them--their scripts; and one script can be used by many
       languages.  Unicode also encodes things that aren't really about
       languages, such as symbols like "BAGGAGE CLAIM".)

       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 the most popular.  UTF-8 is a variable length encoding that
       encodes Unicode characters as 1 to 4 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 perlunicode.

   Perl's Unicode Support
       Starting from Perl v5.6.0, Perl has had the capacity to handle Unicode
       natively.  Perl v5.8.0, 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.  Perl v5.14.0 is
       the first release where Unicode support is (almost) seamlessly
       integrable without some gotchas (the exception being some differences
       in quotemeta, and that is fixed starting in Perl 5.16.0).   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 v5.8.0, 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 v5.8.0, 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 v5.14.0, 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");

       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 the same
       way: 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
       likely 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 added support for Unicode on EBCDIC platforms.  This support
       was allowed to lapse in later releases, but was revived in 5.22.
       Unicode support is somewhat more complex to implement since additional
       conversions are needed.  See perlebcdic for more information.

       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", in that all the basic characters (which includes all
       those that have ASCII equivalents (like "A", "0", "%", etc.)  are the
       same in both EBCDIC and UTF-EBCDIC.  Often, documentation will use the
       term "UTF-8" to mean UTF-EBCDIC as well.  This is the case in this
       document.

   Creating Unicode
       This section applies fully to Perls starting with v5.22.  Various
       caveats for earlier releases are in the "Earlier releases caveats"
       subsection below.

       To create Unicode characters in literals, use the "\N{...}" notation in
       double-quoted strings:

        my $smiley_from_name = "\N{WHITE SMILING FACE}";
        my $smiley_from_code_point = "\N{U+263a}";

       Similarly, they can be used in regular expression literals

        $smiley =~ /\N{WHITE SMILING FACE}/;
        $smiley =~ /\N{U+263a}/;

       At run-time you can use:

        use charnames ();
        my $hebrew_alef_from_name
                             = charnames::string_vianame("HEBREW LETTER ALEF");
        my $hebrew_alef_from_code_point = charnames::string_vianame("U+05D0");

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

       There are other runtime options as well.  You can use "pack()":

        my $hebrew_alef_from_code_point = pack("U", 0x05d0);

       Or you can use "chr()", though it is less convenient in the general
       case:

        $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
        utf8::upgrade($hebrew_alef_from_code_point);

       The "utf8::unicode_to_native()" and "utf8::upgrade()" aren't needed if
       the argument is above 0xFF, so the above could have been written as

        $hebrew_alef_from_code_point = chr(0x05d0);

       since 0x5d0 is above 255.

       "\x{}" and "\o{}" can also be used to specify code points at compile
       time in double-quotish strings, but, for backward compatibility with
       older Perls, the same rules apply as with "chr()" for code points less
       than 256.

       "utf8::unicode_to_native()" is used so that the Perl code is portable
       to EBCDIC platforms.  You can omit it if you're really sure no one will
       ever want to use your code on a non-ASCII platform.  Starting in Perl
       v5.22, calls to it on ASCII platforms are optimized out, so there's no
       performance penalty at all in adding it.  Or you can simply use the
       other constructs that don't require it.

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

       Earlier releases caveats

       On EBCDIC platforms, prior to v5.22, using "\N{U+...}" doesn't work
       properly.

       Prior to v5.16, using "\N{...}" with a character name (as opposed to a
       "U+..." code point) required a "use charnames :full".

       Prior to v5.14, there were some bugs in "\N{...}" with a character name
       (as opposed to a "U+..." code point).

       "charnames::string_vianame()" was introduced in v5.14.  Prior to that,
       "charnames::vianame()" should work, but only if the argument is of the
       form "U+...".  Your best bet there for runtime Unicode by character
       name is probably:

        use charnames ();
        my $hebrew_alef_from_name
                         = pack("U", charnames::vianame("HEBREW LETTER ALEF"));

   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

        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";
           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 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.

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

       The ":locale" does not currently work with "open()" and "binmode()",
       only with the "open" pragma.  The ":utf8" and ":encoding(...)" methods
       do work with all of "open()", "binmode()", and the "open" pragma.

       Similarly, you may use these I/O layers on output streams to
       automatically convert Unicode to the specified encoding when it is
       written to the stream. For example, the following snippet copies the
       contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to
       the file "text.utf8", encoded as UTF-8:

           open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis');
           open(my $unicode, '>:utf8',                  'text.utf8');
           while (<$nihongo>) { print $unicode $_ }

       The naming of encodings, both by the "open()" and by the "open" pragma
       allows for flexible names: "koi8-r" and "KOI8R" will both be
       understood.

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

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

       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 PerlIO, which is the default on most systems.

   Displaying Unicode As Text
       Sometimes you might want to display Perl scalars containing Unicode as
       simple ASCII (or EBCDIC) text.  The following subroutine converts its
       argument so that Unicode characters with code points greater than 255
       are displayed as "\x{...}", control characters (like "\n") are
       displayed as "\x..", and the rest of the characters as themselves:

        sub nice_string {
               join("",
               map { $_ > 255                    # if wide character...
                     ? sprintf("\\x{%04X}", $_)  # \x{...}
                     : chr($_) =~ /[[:cntrl:]]/  # else if control character...
                       ? sprintf("\\x%02X", $_)  # \x..
                       : quotemeta(chr($_))      # else quoted or as themselves
               } unpack("W*", $_[0]));           # unpack Unicode characters
          }

       For example,

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

       returns the string

          'foo\x{0100}bar\x0A'

       which is ready to be printed.

       ("\\x{}" is used here instead of "\\N{}", since it's most likely that
       you want to see what the native values are.)

   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
           <http://www.unicode.org/unicode/reports/tr15> and sections on case
           mapping in the Unicode Standard <http://www.unicode.org>.

           As of Perl 5.8.0, the "Full" case-folding of Case
           Mappings/SpecialCasing is implemented, but bugs remain in "qr//i"
           with them, mostly fixed by 5.14, and essentially entirely by 5.18.

       o   String Collation

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

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

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

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

   Miscellaneous
       o   Character Ranges and Classes

           Character ranges in regular expression 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.

           Starting in v5.22, you can use Unicode code points as the end
           points of regular expression pattern character ranges, and the
           range will include all Unicode code points that lie between those
           end points, inclusive.

            qr/ [\N{U+03]-\N{U+20}] /x

           includes the code points "\N{U+03}", "\N{U+04}", ..., "\N{U+20}".

           (It is planned to extend this behavior to ranges in "tr///" in Perl
           v5.24.)

       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
           generate Unicode data.  The most important thing is getting input
           as Unicode; for that, see the earlier I/O discussion.  To get full
           seamless Unicode support, add "use feature 'unicode_strings'" (or
           "use 5.012" or higher) to your script.

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

           You shouldn't have to care.  But you may if your Perl is before
           5.14.0 or you haven't specified "use feature 'unicode_strings'" or
           "use 5.012" (or higher) because otherwise the rules for the code
           points 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 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 }) {
                   # $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 "Encode":

               use Encode 'from_to';
               from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8

           The call to "from_to()" changes the bytes in $data, but nothing
           material about the nature of the string has changed as far as Perl
           is concerned.  Both before and after the call, the string $data
           contains just a bunch of 8-bit bytes. As far as Perl is concerned,
           the encoding of the string remains as "system-native 8-bit bytes".

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

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

           The contents of the string changes, but not the nature of the
           string.  Perl doesn't know any more after the call than before that
           the contents of the string indicates the affirmative.

           Back to converting data.  If you have (or want) data in your
           system's native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you
           can use pack/unpack to convert to/from Unicode.

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

           If you have a sequence of bytes you know is valid UTF-8, but Perl
           doesn't know it yet, you can make Perl a believer, too:

               use Encode 'decode_utf8';
               $Unicode = decode_utf8($bytes);

           or:

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

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

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

           and you can create well-formed Unicode with

               $Unicode_string = pack("U*", 0xff, ...)

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

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

       o   How Does Unicode Work With Traditional Locales?

           If your locale is a UTF-8 locale, starting in Perl v5.20, Perl
           works well for all categories except "LC_COLLATE" dealing with
           sorting and the "cmp" operator.

           For other locales, starting in Perl 5.16, you can specify

               use locale ':not_characters';

           to get Perl to work well with them.  The catch is that you have to
           translate from the locale character set to/from Unicode yourself.
           See "Unicode I/O" above for how to

               use open ':locale';

           to accomplish this, but full details are in "Unicode and UTF-8" in
           perllocale, including gotchas that happen if you don't specify
           ":not_characters".

   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/>

       o   Unicode Glossary

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

       o   Unicode Recommended Reading List

           The Unicode Consortium has a list of articles and books, some of
           which give a much more in depth treatment of Unicode:
           <http://unicode.org/resources/readinglist.html>

       o   Unicode Useful Resources

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

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

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

       o   UTF-8 and Unicode FAQ for Unix/Linux

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

       o   Legacy Character Sets

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

       o   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(1), perlunicode(1), Encode(3), open(3), utf8(3), bytes(3),
       perlretut(1), perlrun(1), Unicode::Collate(3), Unicode::Normalize(3),
       Unicode::UCD(3)


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>.  Now maintained by
       Perl 5 Porters.

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



perl v5.24.0                      2016-03-01                 PERLUNIINTRO(1pm)

perl 5.24 - Generated Sun Dec 4 20:14:52 CST 2016
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