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Encode(3) - Encode - character encodings - man 3 Encode

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Encode(3)              Perl Programmers Reference Guide              Encode(3)



NAME
       Encode - character encodings

SYNOPSIS
           use Encode;

       Table of Contents

       Encode consists of a collection of modules whose details are too big to
       fit in(1,8) one document.  This POD itself explains the top-level APIs and
       general topics at a glance.  For other topics and more details, see the
       PODs below:

         Name                          Description
         --------------------------------------------------------
         Encode::Alias         Alias definitions to encodings
         Encode::Encoding      Encode Implementation Base Class
         Encode::Supported     List of Supported Encodings
         Encode::CN            Simplified Chinese Encodings
         Encode::JP            Japanese Encodings
         Encode::KR            Korean Encodings
         Encode::TW            Traditional Chinese Encodings
         --------------------------------------------------------

DESCRIPTION
       The "Encode" module provides the interfaces between Perl's strings and
       the rest of the system.  Perl strings are sequences of characters.

       The repertoire of characters that Perl can represent is at least that
       defined by the Unicode Consortium. On most platforms the ordinal values
       of the characters (as returned by "ord(ch)") is the "Unicode codepoint"
       for the character (the exceptions are those platforms where the legacy
       encoding(3,n) is some variant of EBCDIC rather than a super-set of ASCII -
       see perlebcdic).

       Traditionally, computer data has been moved around in(1,8) 8-bit chunks
       often called "bytes". These chunks are also known as "octets" in(1,8) net-
       working standards. Perl is widely used to manipulate data of many types
       - not only strings of characters representing human or computer lan-
       guages but also "binary" data being the machine's representation of
       numbers, pixels in(1,8) an image - or just about anything.

       When Perl is processing "binary data", the programmer wants Perl to
       process "sequences of bytes". This is not a problem for Perl - as a
       byte has 256 possible values, it easily fits in(1,8) Perl's much larger
       "logical character".

       TERMINOLOGY


        character: a character in(1,8) the range 0..(2**32-1) (or more).  (What
         Perl's strings are made of.)

        byte: a character in(1,8) the range 0..255 (A special case of a Perl char-
         acter.)

        octet: 8 bits of data, with ordinal values 0..255 (Term for bytes
         passed to or from a non-Perl context, e.g. a disk file.)

PERL ENCODING API
       $octets  = encode(ENCODING, $string(3,n) [, CHECK])
         Encodes a string(3,n) from Perl's internal form into ENCODING and returns
         a sequence of octets.  ENCODING can be either a canonical name or an
         alias.  For encoding(3,n) names and aliases, see "Defining Aliases".  For
         CHECK, see "Handling Malformed Data".

         For example, to convert a string(3,n) from Perl's internal format to
         iso-8859-1 (also known as Latin1),

           $octets = encode("iso-8859-1", $string(3,n));

         CAVEAT: When you run "$octets = encode("utf8", $string(3,n))", then
         $octets may not be equal to $string.  Though they both contain the
         same data, the utf8 flag for $octets is always off.  When you encode
         anything, utf8 flag of the result is always off, even when it con-
         tains completely valid utf8 string. See "The UTF-8 flag" below.

         encode($valid_encoding, undef) is harmless but warns you for "Use of
         uninitialized value in(1,8) subroutine entry".  encode($valid_encoding,
         '') is harmless and warnless.

       $string(3,n) = decode(ENCODING, $octets [, CHECK])
         Decodes a sequence of octets assumed to be in(1,8) ENCODING into Perl's
         internal form and returns the resulting string.  As in(1,8) encode(),
         ENCODING can be either a canonical name or an alias. For encoding(3,n)
         names and aliases, see "Defining Aliases".  For CHECK, see "Handling
         Malformed Data".

         For example, to convert ISO-8859-1 data to a string(3,n) in(1,8) Perl's inter-
         nal format:

           $string(3,n) = decode("iso-8859-1", $octets);

         CAVEAT: When you run "$string(3,n) = decode("utf8", $octets)", then
         $string(3,n) may not be equal to $octets.  Though they both contain the
         same data, the utf8 flag for $string(3,n) is on unless $octets entirely
         consists of ASCII data (or EBCDIC on EBCDIC machines).  See "The
         UTF-8 flag" below.

         decode($valid_encoding, undef) is harmless but warns you for "Use of
         uninitialized value in(1,8) subroutine entry".  decode($valid_encoding,
         '') is harmless and warnless.

       [$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])
         Converts in-place data between two encodings. The data in(1,8) $octets
         must be encoded as octets and not as characters in(1,8) Perl's internal
         format. For example, to convert ISO-8859-1 data to Microsoft's CP1250
         encoding:

           from_to($octets, "iso-8859-1", "cp1250");

         and to convert it back:

           from_to($octets, "cp1250", "iso-8859-1");

         Note that because the conversion happens in(1,8) place, the data to be
         converted cannot be a string(3,n) constant; it must be a scalar variable.

         from_to() returns the length of the converted string(3,n) in(1,8) octets on
         success, undef otherwise.

         CAVEAT: The following operations look(1,8,3 Search::Dict) the same but are not quite so;

           from_to($data, "iso-8859-1", "utf8"); #1
           $data = decode("iso-8859-1", $data);  #2

         Both #1 and #2 make $data consist of a completely valid UTF-8 string(3,n)
         but only #2 turns utf8 flag on.  #1 is equivalent to

           $data = encode("utf8", decode("iso-8859-1", $data));

         See "The UTF-8 flag" below.

       $octets = encode_utf8($string(3,n));
         Equivalent to "$octets = encode("utf8", $string(3,n));" The characters
         that comprise $string(3,n) are encoded in(1,8) Perl's internal format and the
         result is returned as a sequence of octets. All possible characters
         have a UTF-8 representation so this function cannot fail.

       $string(3,n) = decode_utf8($octets [, CHECK]);
         equivalent to "$string(3,n) = decode("utf8", $octets [, CHECK])".  The
         sequence of octets represented by $octets is decoded from UTF-8 into
         a sequence of logical characters. Not all sequences of octets form
         valid UTF-8 encodings, so it is possible for this call to fail.  For
         CHECK, see "Handling Malformed Data".

       Listing available encodings

         use Encode;
         @list = Encode->encodings();

       Returns a list of the canonical names of the available encodings that
       are loaded.  To get a list of all available encodings including the
       ones that are not loaded yet, say

         @all_encodings = Encode->encodings(":all");

       Or you can give the name of a specific module.

         @with_jp = Encode->encodings("Encode::JP");

       When "::" is not in(1,8) the name, "Encode::" is assumed.

         @ebcdic = Encode->encodings("EBCDIC");

       To find out in(1,8) detail which encodings are supported by this package,
       see Encode::Supported.

       Defining Aliases

       To add a new alias to a given encoding(3,n), use:

         use Encode;
         use Encode::Alias;
         define_alias(newName => ENCODING);

       After that, newName can be used as an alias for ENCODING.  ENCODING may
       be either the name of an encoding(3,n) or an encoding(3,n) object

       But before you do so, make sure the alias is nonexistent with
       "resolve_alias()", which returns the canonical name thereof.  i.e.

         Encode::resolve_alias("latin1") eq "iso-8859-1" # true
         Encode::resolve_alias("iso-8859-12")   # false; nonexistent
         Encode::resolve_alias($name) eq $name  # true if(3,n) $name is canonical

       resolve_alias() does not need "use Encode::Alias"; it can be exported
       via "use Encode qw(resolve_alias)".

       See Encode::Alias for details.

Encoding via PerlIO
       If your perl supports PerlIO (which is the default), you can use a Per-
       lIO layer to decode and encode directly via a filehandle.  The follow-
       ing two examples are totally identical in(1,8) their functionality.

         # via PerlIO
         open(2,3,n) my $in(1,8),  "<:encoding(shiftjis)", $infile  or die;
         open(2,3,n) my $out, ">:encoding(euc-jp)",   $outfile or die;
         while(<$in(1,8)>){ print $out $_; }

         # via from_to
         open(2,3,n) my $in(1,8),  "<", $infile  or die;
         open(2,3,n) my $out, ">", $outfile or die;
         while(<$in(1,8)>){
           from_to($_, "shiftjis", "euc-jp", 1);
           print $out $_;
         }

       Unfortunately, it may be that encodings are PerlIO-savvy.  You can
       check if(3,n) your encoding(3,n) is supported by PerlIO by calling the "per-
       lio_ok" method.

         Encode::perlio_ok("hz");             # False
         find_encoding("euc-cn")->perlio_ok;  # True where PerlIO is available

         use Encode qw(perlio_ok);            # exported upon request
         perlio_ok("euc-jp")

       Fortunately, all encodings that come with Encode core are PerlIO-savvy
       except for hz and ISO-2022-kr.  For gory details, see Encode::Encoding
       and Encode::PerlIO.

Handling Malformed Data
       The CHECK argument is used as follows.  When you omit it, the behaviour
       is the same as if(3,n) you had passed a value of 0 for CHECK.

       CHECK = Encode::FB_DEFAULT ( == 0)
         If CHECK is 0, (en|de)code will put a substitution character in(1,8) place
         of a malformed character.  For UCM-based encodings, <subchar> will be
         used.  For Unicode, the code point 0xFFFD is used.  If the data is
         supposed to be UTF-8, an optional lexical warning (category utf8) is
         given.

       CHECK = Encode::FB_CROAK ( == 1)
         If CHECK is 1, methods will die on error(8,n) immediately with an error(8,n)
         message.  Therefore, when CHECK is set(7,n,1 builtins) to 1,  you should trap the
         fatal error(8,n) with eval{} unless you really want to let it die on
         error.

       CHECK = Encode::FB_QUIET
         If CHECK is set(7,n,1 builtins) to Encode::FB_QUIET, (en|de)code will immediately
         return the portion of the data that has been processed so far when an
         error(8,n) occurs. The data argument will be overwritten with everything
         after that point (that is, the unprocessed part of data).  This is
         handy when you have to call decode repeatedly in(1,8) the case where your
         source data may contain partial multi-byte character sequences, for
         example because you are reading with a fixed-width buffer. Here is
         some sample code that does exactly this:

           my $data = ''; my $utf8 = '';
           while(defined(read(2,n,1 builtins) $fh, $buffer, 256)){
             # buffer may end in(1,8) a partial character so we append
             $data .= $buffer;
             $utf8 .= decode($encoding(3,n), $data, Encode::FB_QUIET);
             # $data now contains the unprocessed partial character
           }

       CHECK = Encode::FB_WARN
         This is the same as above, except that it warns on error.  Handy when
         you are debugging the mode above.

       perlqq mode (CHECK = Encode::FB_PERLQQ)
       HTML charref mode (CHECK = Encode::FB_HTMLCREF)
       XML charref mode (CHECK = Encode::FB_XMLCREF)
         For encodings that are implemented by Encode::XS, CHECK ==
         Encode::FB_PERLQQ turns (en|de)code into "perlqq" fallback mode.

         When you decode, "\xHH" will be inserted for a malformed character,
         where HH is the hex representation of the octet  that could not be
         decoded to utf8.  And when you encode, "\x{HHHH}" will be inserted,
         where HHHH is the Unicode ID of the character that cannot be found in(1,8)
         the character repertoire of the encoding.

         HTML/XML character reference modes are about the same, in(1,8) place of
         "\x{HHHH}", HTML uses "&#NNNN"; where NNNN is a decimal digit and XML
         uses "&#xHHHH"; where HHHH is the hexadecimal digit.

       The bitmask
         These modes are actually set(7,n,1 builtins) via a bitmask.  Here is how the FB_XX
         constants are laid out.  You can import the FB_XX constants via "use
         Encode qw(:fallbacks)"; you can import the generic bitmask constants
         via "use Encode qw(:fallback_all)".

                              FB_DEFAULT FB_CROAK FB_QUIET FB_WARN  FB_PERLQQ
          DIE_ON_ERR    0x0001             X
          WARN_ON_ERR   0x0002                               X
          RETURN_ON_ERR 0x0004                      X        X
          LEAVE_SRC     0x0008
          PERLQQ        0x0100                                        X
          HTMLCREF      0x0200
          XMLCREF       0x0400

       Unimplemented fallback schemes

       In the future, you will be able to use a code reference to a callback
       function for the value of CHECK but its API is still undecided.

       The fallback scheme does not work on EBCDIC platforms.

Defining Encodings
       To define a new encoding(3,n), use:

           use Encode qw(define_encoding);
           define_encoding($object, 'canonicalName' [, alias...]);

       canonicalName will be associated with $object.  The object should pro-
       vide the interface described in(1,8) Encode::Encoding.  If more than two
       arguments are provided then additional arguments are taken as aliases
       for $object.

       See Encode::Encoding for more details.

The UTF-8 flag
       Before the introduction of utf8 support in(1,8) perl, The "eq" operator just
       compared the strings represented by two scalars. Beginning with perl
       5.8, "eq" compares two strings with simultaneous consideration of the
       utf8 flag. To explain why we made it so, I will quote page 402 of "Pro-
       gramming Perl, 3rd ed."

       Goal #1:
         Old byte-oriented programs should not spontaneously break on the old
         byte-oriented data they used to work on.

       Goal #2:
         Old byte-oriented programs should magically start working on the new
         character-oriented data when appropriate.

       Goal #3:
         Programs should run just as fast in(1,8) the new character-oriented mode
         as in(1,8) the old byte-oriented mode.

       Goal #4:
         Perl should remain one language, rather than forking into a byte-ori-
         ented Perl and a character-oriented Perl.

       Back when "Programming Perl, 3rd ed." was written, not even Perl 5.6.0
       was born and many features documented in(1,8) the book remained unimple-
       mented for a long time.  Perl 5.8 corrected this and the introduction
       of the UTF-8 flag is one of them.  You can think of this perl notion as
       of a byte-oriented mode (utf8 flag off) and a character-oriented mode
       (utf8 flag on).

       Here is how Encode takes care of the utf8 flag.

        When you encode, the resulting utf8 flag is always off.

        When you decode, the resulting utf8 flag is on unless you can unam-
         biguously represent data.  Here is the definition of dis-ambiguity.

         After "$utf8 = decode('foo', $octet);",

           When $octet is...   The utf8 flag in(1,8) $utf8 is
           ---------------------------------------------
           In ASCII only (or EBCDIC only)            OFF
           In ISO-8859-1                              ON
           In any other Encoding                      ON
           ---------------------------------------------

         As you see, there is one exception, In ASCII.  That way you can assue
         Goal #1.  And with Encode Goal #2 is assumed but you still have to be
         careful in(1,8) such cases mentioned in(1,8) CAVEAT paragraphs.

         This utf8 flag is not visible in(1,8) perl scripts, exactly for the same
         reason you cannot (or you don't have to) see if(3,n) a scalar contains a
         string(3,n), integer, or floating point number.   But you can still peek
         and poke these if(3,n) you will.  See the section below.

       Messing with Perl's Internals

       The following API uses parts of Perl's internals in(1,8) the current imple-
       mentation.  As such, they are efficient but may change.

       is_utf8(STRING [, CHECK])
         [INTERNAL] Tests whether the UTF-8 flag is turned on in(1,8) the STRING.
         If CHECK is true, also checks the data in(1,8) STRING for being well-
         formed UTF-8.  Returns true if(3,n) successful, false otherwise.

         As of perl 5.8.1, utf8 also has utf8::is_utf8().

       _utf8_on(STRING)
         [INTERNAL] Turns on the UTF-8 flag in(1,8) STRING.  The data in(1,8) STRING is
         not checked for being well-formed UTF-8.  Do not use unless you know
         that the STRING is well-formed UTF-8.  Returns the previous state of
         the UTF-8 flag (so please don't treat the return value as indicating
         success or failure), or "undef" if(3,n) STRING is not a string.

       _utf8_off(STRING)
         [INTERNAL] Turns off the UTF-8 flag in(1,8) STRING.  Do not use
         frivolously.  Returns the previous state of the UTF-8 flag (so please
         don't treat the return value as indicating success or failure), or
         "undef" if(3,n) STRING is not a string.

SEE ALSO
       Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding(3,n), per-
       lebcdic, "open(2,3,n)" in(1,8) perlfunc, perlunicode, utf8, the Perl Unicode Mail-
       ing List <perl-unicode@perl.org>

MAINTAINER
       This project was originated by Nick Ing-Simmons and later maintained by
       Dan Kogai <dankogai@dan.co.jp>.  See AUTHORS for a full list of people
       involved.  For any questions, use <perl-unicode@perl.org> so we can all
       share.



perl v5.8.5                       2001-09-21                         Encode(3)

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