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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	       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".

   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 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 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(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 v5.16.3			  2013-03-06			   Encode(3pm)
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