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




NAME

       Encode - character encodings in Perl


SYNOPSIS

           use Encode qw(decode encode);
           $characters = decode('UTF-8', $octets,     Encode::FB_CROAK);
           $octets     = encode('UTF-8', $characters, Encode::FB_CROAK);

   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:

       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 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".

       This document mostly explains the how. perlunitut and perlunifaq
       explain the why.

   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, standard I/O stream,
       database, command-line argument, environment variable, socket etc.


THE PERL ENCODING API

   Basic methods
       encode

         $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.

       decode

         $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.  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.  See "The UTF8 flag" below.

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

       find_encoding

         [$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.

       from_to

         [$length =] from_to($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 to:

         $octets = encode($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);

       encode_utf8

         $octets = encode_utf8($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.

       decode_utf8

         $string = decode_utf8($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 therefore
       added.

         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 not "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 encodings support this feature.  Some encodings ignore
       the CHECK argument.  For example, Encode::Unicode ignores CHECK and it
       always croaks on error.

   List of CHECK values
       FB_DEFAULT

         I<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.

       FB_CROAK

         I<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".

       FB_QUIET

         I<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
           }

       FB_WARN

         I<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.

       FB_PERLQQ FB_HTMLCREF FB_XMLCREF

       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

       LEAVE_SRC

         Encode::LEAVE_SRC

       If the "Encode::LEAVE_SRC" bit is not set but CHECK is set, then the
       source string 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 character as an argument and returns
       octets that represent 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}".

       Even the fallback for "decode" must return octets, which are then
       decoded with the character encoding that "decode" accepts. So for
       example if you wish to decode octets as UTF-8, and use ISO-8859-15 as a
       fallback for bytes that are not valid UTF-8, you could write

           $str = decode 'UTF-8', $octets, sub {
               my $tmp = chr shift;
               from_to $tmp, 'ISO-8859-15', 'UTF-8';
               return $tmp;
           };


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 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.

       o When you encode, the resulting UTF8 flag is always off.

       o 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 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 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

         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

         _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

         _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
       <http://lists.perl.org/list/perl-unicode.html>


MAINTAINER

       This project was originated by the late Nick Ing-Simmons and later
       maintained by Dan Kogai <dankogai@cpan.org>.  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 2002-2014 Dan Kogai <dankogai@cpan.org>.

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



perl v5.24.0                      2016-03-01                       Encode(3pm)

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