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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 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 is some variant of EBCDIC rather
       than a super-set of ASCII - see perlebcdic).

       Traditionally, computer data has been moved around in 8-bit chunks often called "bytes". These chunks are also
       known as "octets" in networking standards. Perl is widely used to manipulate data of many types - not only
       strings of characters representing human or computer languages but also "binary" data being the machine's rep-
       resentation of numbers, pixels in 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 Perl's much larger "logical character".

       TERMINOLOGY


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

       ? byte: a character in the range 0..255 (A special case of a Perl character.)

       ? 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 [, CHECK])
         Encodes a string 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 names and aliases, see "Defining Aliases".  For CHECK, see
         "Handling Malformed Data".

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

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

         CAVEAT: When you run "$octets = encode("utf8", $string)", 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 contains completely valid utf8 string. See "The UTF-8 flag"
         below.

         If the $string is "undef" then "undef" is returned.

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

         For example, to convert ISO-8859-1 data to a string in Perl's internal format:

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

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

         If the $string is "undef" then "undef" is returned.

       [$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])
         Converts in-place data between two encodings. The data in $octets must be encoded as octets and not as char-
         acters in 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 place, the data to be converted cannot be a string constant; it
         must be a scalar variable.

         from_to() returns the length of the converted string in octets on success, undef on error.

         CAVEAT: The following operations look 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 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);
         Equivalent to "$octets = encode("utf8", $string);" The characters that comprise $string are encoded in Perl's
         internal format and the result is returned as a sequence of octets. All possible characters have a UTF-8 rep-
         resentation so this function cannot fail.

       $string = decode_utf8($octets [, CHECK]);
         equivalent to "$string = 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 avail-
       able 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 the name, "Encode::" is assumed.

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

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

       Defining Aliases

       To add a new alias to a given encoding, 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 or an
       encoding 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 $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 PerlIO layer to decode and encode directly
       via a filehandle.  The following two examples are totally identical in their functionality.

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

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

       Unfortunately, it may be that encodings are PerlIO-savvy.  You can check if your encoding is supported by Per-
       lIO by calling the "perlio_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 optional CHECK argument tells Encode what to do when it encounters malformed data.  Without CHECK,
       Encode::FB_DEFAULT ( == 0 ) is assumed.

       As of version 2.12 Encode supports coderef values for CHECK.  See below.

       NOTE: Not all encoding support this feature
         Some encodings ignore CHECK argument.  For example, Encode::Unicode ignores CHECK and it always croaks on
         error.

       Now here is the list of CHECK values available

       CHECK = Encode::FB_DEFAULT ( == 0)
         If CHECK is 0, (en|de)code will put a substitution character in place of a malformed character.  When you
         encode, <subchar> will be used.  When you decode 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 immediately with an error message.  Therefore, when CHECK is set to
         1,  you should trap the error with eval{} unless you really want to let it die.

       CHECK = Encode::FB_QUIET
         If CHECK is set to Encode::FB_QUIET, (en|de)code will immediately return the portion of the data that has
         been processed so far when an error 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 the
         case where your source data may contain partial multi-byte character sequences, (i.e. you are reading with a
         fixed-width buffer). Here is a sample code that does exactly this:

           my $buffer = ''; my $string = '';
           while(read $fh, $buffer, 256, length($buffer)){
             $string .= decode($encoding, $buffer, Encode::FB_QUIET);
             # $buffer 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 the character repertoire of the encoding.

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

         In Encode 2.10 or later, "LEAVE_SRC" is also implied.

       The bitmask
         These modes are actually set 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                                        X
          PERLQQ        0x0100                                        X
          HTMLCREF      0x0200
          XMLCREF       0x0400

       coderef for CHECK

       As of Encode 2.12 CHECK can also be a code reference which takes the ord value of unmapped caharacter as an
       argument and returns a string that represents the fallback character.  For instance,

         $ascii = encode("ascii", $utf8, sub{ sprintf "<U+%04X>", shift });

       Acts like FB_PERLQQ but <U+XXXX> is used instead of \x{XXXX}.

Defining Encodings
       To define a new encoding, use:

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

       canonicalName will be associated with $object.  The object should provide the interface described in
       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 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 "Programming 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 appropri-
         ate.

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

       Goal #4:
         Perl should remain one language, rather than forking into a byte-oriented 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
       the book remained unimplemented 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 char-
       acter-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 unambiguously represent data.  Here is the def-
         inition of dis-ambiguity.

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

           When $octet is...   The utf8 flag in $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 assume Goal #1.  And with Encode Goal #2 is
         assumed but you still have to be careful in such cases mentioned in CAVEAT paragraphs.

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

       Messing with Perl's Internals

       The following API uses parts of Perl's internals in the current implementation.  As such, they are efficient
       but may change.

       is_utf8(STRING [, CHECK])
         [INTERNAL] Tests whether the UTF-8 flag is turned on in the STRING.  If CHECK is true, also checks the data
         in STRING for being well-formed UTF-8.  Returns true if 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 STRING.  The data in 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 STRING is not a
         string.

       _utf8_off(STRING)
         [INTERNAL] Turns off the UTF-8 flag in 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 STRING is
         not a string.

UTF-8 vs. utf8
         ....We now view strings not as sequences of bytes, but as sequences
         of numbers in the range 0 .. 2**32-1 (or in the case of 64-bit
         computers, 0 .. 2**64-1) -- Programming Perl, 3rd ed.

       That has been the perl's notion of UTF-8 but official UTF-8 is more strict; Its ranges is much narrower (0 ..
       10FFFF), some sequences are not allowed (i.e. Those used in the surrogate pair, 0xFFFE, et al).

       Now that is overruled by Larry Wall himself.

         From: Larry Wall <larryATwall.org>
         Date: December 04, 2004 11:51:58 JST
         To: perl-unicodeATperl.org
         Subject: Re: Make Encode.pm support the real UTF-8
         Message-Id: <20041204025158.GA28754ATwall.org>

         On Fri, Dec 03, 2004 at 10:12:12PM +0000, Tim Bunce wrote:
         : I've no problem with 'utf8' being perl's unrestricted uft8 encoding,
         : but "UTF-8" is the name of the standard and should give the
         : corresponding behaviour.

         For what it's worth, that's how I've always kept them straight in my
         head.

         Also for what it's worth, Perl 6 will mostly default to strict but
         make it easy to switch back to lax.

         Larry

       Do you copy?  As of Perl 5.8.7, UTF-8 means strict, official UTF-8 while utf8 means liberal, lax, version
       thereof.  And Encode version 2.10 or later thus groks the difference between "UTF-8" and C"utf8".

         encode("utf8",  "\x{FFFF_FFFF}", 1); # okay
         encode("UTF-8", "\x{FFFF_FFFF}", 1); # croaks

       "UTF-8" in Encode is actually a canonical name for "utf-8-strict".  Yes, the hyphen between "UTF" and "8" is
       important.  Without it Encode goes "liberal"

         find_encoding("UTF-8")->name # is 'utf-8-strict'
         find_encoding("utf-8")->name # ditto. names are case insensitive
         find_encoding("utf8")->name  # ditto. "_" are treated as "-"
         find_encoding("UTF8")->name  # is 'utf8'.

SEE ALSO
       Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding, perlebcdic, "open" in perlfunc, perlunicode,
       utf8, the Perl Unicode Mailing List <perl-unicodeATperl.org>

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



perl v5.8.8                       2001-09-21                         Encode(3)