MirOS Manual: Encode(3p)


ext::Encode::EncoPerlpProgrammers Referencext::Encode::Encode(3p)

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 plat-
     forms 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 charac-
     ters representing human or computer languages but also
     "binary" data being the machine's representation 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".

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     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 for-
       mat 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 canoni-
       cal 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.

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       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 characters 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 represen-
       tation 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".

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     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 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 encod-
     ing 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 identi-
     cal in their functionality.

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       # 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 PerlIO 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 charac-
       ter 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

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       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)".

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                            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 appropriate.

     Goal #3:
       Programs should run just as fast in the new character-

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       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 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 unambiguously represent data.  Here is the definition
       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

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       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 suc-
       cess 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 sur-
     rogate pair, 0xFFFE, et al).

     Now that is overruled by Larry Wall himself.

       From: Larry Wall <larry@wall.org>
       Date: December 04, 2004 11:51:58 JST
       To: perl-unicode@perl.org
       Subject: Re: Make Encode.pm support the real UTF-8
       Message-Id: <20041204025158.GA28754@wall.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

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     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, encod-
     ing, perlebcdic, "open" in perlfunc, perlunicode, utf8, the
     Perl Unicode Mailing 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.

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