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



NAME
       Encode - character encodings in Perl

SYNOPSIS
           use Encode;

   Table of Contents
       Encode consists of a collection of modules whose details are too extensive to fit in one document.
       This one itself explains the top-level APIs and general topics at a glance.  For other topics and
       more details, see the documentation for these modules:

         Name                          Description
         --------------------------------------------------------Encode::Alias -------------------------------------------------------Encode::Alias
         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 -------------------------------------------------------DESCRIPTION

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

       The repertoire of characters that Perl can represent is a superset of those defined by the Unicode
       Consortium. On most platforms the ordinal values of a character as returned by "ord(S)" is the
       Unicode codepoint for that character. The exceptions are platforms where the legacy encoding is some
       variant of EBCDIC rather than a superset of ASCII; see perlebcdic.

       During recent history, data is moved around a computer in 8-bit chunks, often called "bytes" but also
       known as "octets" in standards documents.  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 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: because 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, such as a disk file.

THE PERL ENCODING API
       $octets  = encode(ENCODING, STRING[, CHECK])
         Encodes the scalar value 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 into ISO-8859-1, also known as Latin1:

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

         CAVEAT: When you run "$octets = encode("utf8", $string)", then $octets might not be equal to
         $string.  Though both contain the same data, the UTF8 flag for $octets is always off.  When you
         encode anything, the UTF8 flag on the result is always off, even when it contains a completely
         valid utf8 string. See "The UTF8 flag" below.

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

       $string = decode(ENCODING, OCTETS[, CHECK])
         This function returns the string that results from decoding the scalar value OCTETS, assumed to be
         a sequence of octets in ENCODING, into Perl's internal form.  The returns the resulting string.  As
         with 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 into a string in Perl's internal format:

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

         CAVEAT: When you run "$string = decode("utf8", $octets)", then $string might not be equal to
         $octets.  Though both contain the same data, the UTF8 flag for $string is on unless $octets
         consists entirely of ASCII data on ASCII machines or EBCDIC on EBCDIC machines.  See "The UTF8
         flag" below.

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

       [$obj =] find_encoding(ENCODING)
         Returns the encoding object corresponding to ENCODING.  Returns "undef" if no matching ENCODING is
         find.  The returned object is what does the actual encoding or decoding.

           $utf8 = decode($name, $bytes);

         is in fact

             $utf8 = do {
                 $obj = find_encoding($name);
                 croak qq(encoding "$name" not found) unless ref $obj;
                 $obj->decode($bytes);
             };

         with more error checking.

         You can therefore save time by reusing this object as follows;

             my $enc = find_encoding("iso-8859-1");
             while(<>) {
                 my $utf8 = $enc->decode($_);
                 ... # now do something with $utf8;
             }

         Besides "->decode" and "->encode", other methods are available as well.  For instance, "->name"
         returns the canonical name of the encoding object.

           find_encoding("latin1")->name; # iso-8859-1

         See Encode::Encoding for details.

       [$length =] from_to($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 into Microsoft's
         CP1250 encoding:

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

         and to convert it back:

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

         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, and "undef" on error.

         CAVEAT: The following operations may look the same, but are not:

           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 the UTF8
         flag on.  #1 is equivalent to:

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

         See "The UTF8 flag" below.

         Also note that:

           from_to($octets, $from, $to, $check);

         is equivalent t:o

           $octets = encode($to, decode($from, $octets), $check);

         Yes, it does not respect the $check during decoding.  It is deliberately done that way.  If you
         need minute control, use "decode" followed by "encode" as follows:

           $octets = encode($to, decode($from, $octets, $check_from), $check_to);

       $octets = encode_utf8($string);
         Equivalent to "$octets = encode("utf8", $string)".  The characters in $string are encoded in Perl's
         internal format, and the result is returned as a sequence of octets.  Because all possible
         characters in Perl have a (loose, not strict) UTF-8 representation, 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.  Because not all sequences of
         octets are valid UTF-8, it is quite possible for this function to fail.  For CHECK, see "Handling
         Malformed Data".

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

       Returns a list of canonical names of available encodings that have already been loaded.  To get a
       list of all available encodings including those that have not yet been loaded, 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.

       Before you do that, first make sure the alias is nonexistent using "resolve_alias()", which returns
       the canonical name thereof.  For example:

         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 imported via "use Encode
       qw(resolve_alias)".

       See Encode::Alias for details.

   Finding IANA Character Set Registry names
       The canonical name of a given encoding does not necessarily agree with IANA Character Set Registry,
       commonly seen as "Content-Type: text/plain; charset=WHATEVER".  For most cases, the canonical name
       works, but sometimes it does not, most notably with "utf-8-strict".

       As of "Encode" version 2.21, a new method "mime_name()" is thereforeadded.

         use Encode;
         my $enc = find_encoding("UTF-8");
         warn $enc->name;      # utf-8-strict
         warn $enc->mime_name; # UTF-8

       See also:  Encode::Encoding

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 fully identical in functionality:

         ### Version 1 via PerlIO
           open(INPUT,  "< :encoding(shiftjis)", $infile)
               || die "Can't open < $infile for reading: $!";
           open(OUTPUT, "> :encoding(euc-jp)",  $outfile)
               || die "Can't open > $output for writing: $!";
           while (<INPUT>) {   # auto decodes $_
               print OUTPUT;   # auto encodes $_
           }
           close(INPUT)   || die "can't close $infile: $!";
           close(OUTPUT)  || die "can't close $outfile: $!";

         ### Version 2 via from_to()
           open(INPUT,  "< :raw", $infile)
               || die "Can't open < $infile for reading: $!";
           open(OUTPUT, "> :raw",  $outfile)
               || die "Can't open > $output for writing: $!";

           while (<INPUT>) {
               from_to($_, "shiftjis", "euc-jp", 1);  # switch encoding
               print OUTPUT;   # emit raw (but properly encoded) data
           }
           close(INPUT)   || die "can't close $infile: $!";
           close(OUTPUT)  || die "can't close $outfile: $!";

       In the first version above, you let the appropriate encoding layer handle the conversion.  In the
       second, you explicitly translate from one encoding to the other.

       Unfortunately, it may be that encodings are "PerlIO"-savvy.  You can check to see whether your
       encoding is supported by "PerlIO" by invoking the "perlio_ok" method on it:

         Encode::perlio_ok("hz");             # false
         find_encoding("euc-cn")->perlio_ok;  # true wherever PerlIO is available

         use Encode qw(perlio_ok);            # imported 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 the gory details, see Encode::Encoding and Encode::PerlIO.

Handling Malformed Data
       The optional CHECK argument tells "Encode" what to do when encountering 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, encoding and decoding replace any malformed character with a substitution character.
         When you encode, SUBCHAR is used.  When you decode, the Unicode REPLACEMENT CHARACTER, code point
         U+FFFD, is used.  If the data is supposed to be UTF-8, an optional lexical warning of warning
         category "utf8" is given.

       CHECK = Encode::FB_CROAK ( == 1)
         If CHECK is 1, methods immediately die with an error message.  Therefore, when CHECK is 1, you
         should trap exceptions with "eval{}", unless you really want to let it "die".

       CHECK = Encode::FB_QUIET
         If CHECK is set to "Encode::FB_QUIET", encoding and decoding immediately return the portion of the
         data that has been processed so far when an error occurs. The data argument is overwritten with
         everything after that point; that is, the unprocessed portion of the 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, (that is, you are reading with a fixed-width buffer). Here's some sample code
         to do exactly that:

             my($buffer, $string) = ("", "");
             while (read($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 "FB_QUIET" above, except that instead of being silent on errors, it issues a
         warning.  This is handy for when you are debugging.

       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 the "Encode::XS" module, "CHECK" "==" "Encode::FB_PERLQQ"
         puts "encode" and "decode" into "perlqq" fallback mode.

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

         The 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 all actually set via a bitmask.  Here is how the "FB_XXX" constants are laid out.
         You can import the "FB_XXX" constants via "use Encode qw(:fallbacks)", and 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

       Encode::LEAVE_SRC
         If the "Encode::LEAVE_SRC" bit is not set but CHECK is set, then the second argument to encode() or
         decode() will be overwritten in place.  If you're not interested in this, then bitwise-OR it with
         the bitmask.

   coderef for CHECK
       As of "Encode" 2.12, "CHECK" can also be a code reference which takes the ordinal value of the
       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, CANONICAL_NAME [, alias...]);

       CANONICAL_NAME will be associated with $object.  The object should provide the interface described in
       Encode::Encoding.  If more than two arguments are provided, additional arguments are considered
       aliases for $object.

       See Encode::Encoding for details.

The UTF8 flag
       Before the introduction of Unicode 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 quote from 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-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 characteroriented
         oriented Perl.

       When Programming Perl, 3rd ed. was written, not even Perl 5.6.0 had been born yet, many features
       documented in the book remained unimplemented for a long time.  Perl 5.8 corrected much of this, and
       the introduction of the UTF8 flag is one of them.  You can think of there being two fundamentally
       different kinds of strings and string-operations in Perl: one a byte-oriented mode  for when the
       internal UTF8 flag is off, and the other a character-oriented mode for when the internal UTF8 flag is
       on.

       Here is how "Encode" handles 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 what we mean by "unambiguously".  After "$utf8 = decode("foo", $octet)",

           When $octet is...   The UTF8 flag in $utf8 is
           ---------------------------------------------In --------------------------------------------In
           In ASCII only (or EBCDIC only)            OFF
           In ISO-8859-1                              ON
           In any other Encoding                      ON
           ---------------------------------------------As --------------------------------------------As

         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 the cases mentioned in the CAVEAT paragraphs
         above.

         This UTF8 flag is not visible in Perl scripts, exactly for the same reason you cannot (or rather,
         you don't have to) see whether a scalar contains a string, an integer, or a floating-point number.
         But you can still peek and poke these if you will.  See the next section.

   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 in a future release.

       is_utf8(STRING [, CHECK])
         [INTERNAL] Tests whether the UTF8 flag is turned on in the STRING.  If CHECK is true, also checks
         whether STRING contains well-formed UTF-8.  Returns true if successful, false otherwise.

         As of Perl 5.8.1, utf8 also has the "utf8::is_utf8" function.

       _utf8_on(STRING)
         [INTERNAL] Turns the STRING's internal UTF8 flag on.  The STRING is not checked for containing only
         well-formed UTF-8.  Do not use this unless you know with absolute certainty that the STRING holds
         only well-formed UTF-8.  Returns the previous state of the UTF8 flag (so please don't treat the
         return value as indicating success or failure), or "undef" if STRING is not a string.

         NOTE: For security reasons, this function does not work on tainted values.

       _utf8_off(STRING)
         [INTERNAL] Turns the STRING's internal UTF8 flag off.  Do not use frivolously.  Returns the
         previous state of the UTF8 flag, or "undef" if STRING is not a string.  Do not treat the return
         value as indicative of success or failure, because that isn't what it means: it is only the
         previous setting.

         NOTE: For security reasons, this function does not work on tainted values.

UTF-8 vs. utf8 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 historically been Perl's notion of UTF-8, as that is how UTF-8 was first conceived by Ken
       Thompson when he invented it. However, thanks to later revisions to the applicable standards,
       official UTF-8 is now rather stricter than that. For example, its range is much narrower (0 ..
       0x10_FFFF to cover only 21 bits instead of 32 or 64 bits) and some sequences are not allowed, like
       those used in surrogate pairs, the 31 non-character code points 0xFDD0 .. 0xFDEF, the last two code
       points in any plane (0xXX_FFFE and 0xXX_FFFF), all non-shortest encodings, etc.

       The former default in which Perl would always use a loose interpretation of UTF-8 has now been
       overruled:

         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

       Got that?  As of Perl 5.8.7, "UTF-8" means UTF-8 in its current sense, which is conservative and
       strict and security-conscious, whereas "utf8" means UTF-8 in its former sense, which was liberal and
       loose and lax.  "Encode" version 2.10 or later thus groks this subtle but critically important
       distinction between "UTF-8" and "utf8".

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

       In the "Encode" module, "UTF-8" is actually a canonical name for "utf-8-strict".  That hyphen between
       the "UTF" and the "8" is critical; without it, "Encode" goes "liberal" and (perhaps
       overly-)permissive:

         find_encoding("UTF-8")->name # is 'utf-8-strict'
         find_encoding("utf-8")->name # ditto. names are case insensitive
         find_encoding("utf_8")->name # ditto. "_" are treated as "-"
         find_encoding("UTF8")->name  # is 'utf8'.

       Perl's internal UTF8 flag is called "UTF8", without a hyphen. It indicates whether a string is
       internally encoded as "utf8", also without a hyphen.

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

MAINTAINER
       This project was originated by the late 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, send mail
       to <perl-unicode@perl.org> so that we can all share.

       While Dan Kogai retains the copyright as a maintainer, credit should go to all those involved.  See
       AUTHORS for a list of those who submitted code to the project.

COPYRIGHT
       Copyright 2002-2011 Dan Kogai <dankogai@dan.co.jp>.

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.



perl v5.16.2                                     2012-10-25                                      Encode(3pm)