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RedHat 9 (Linux i386) - man page for encode (redhat section 3pm)

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

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 docu-
       ment.  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 Uni-
       code Consortium. On most platforms the ordinal values of the characters (as returned by
       "ord(ch)") is the "Unicode codepoint" for the character (the exceptions are those plat-
       forms where the legacy encoding is some variant of EBCDIC rather than a super-set of ASCII
       - see perlebcdic).

       Traditionally, computer data has been moved around in 8-bit chunks often called "bytes".
       These chunks are also known as "octets" in networking standards. Perl is widely used to
       manipulate data of many types - not only strings of characters representing human or com-
       puter languages but also "binary" data being the machine's representation of numbers, pix-
       els in an image - or just about anything.

       When Perl is processing "binary data", the programmer wants Perl to process "sequences of
       bytes". This is not a problem for Perl - as a byte has 256 possible values, it easily fits
       in Perl's much larger "logical character".

       TERMINOLOGY

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

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

       o octet: 8 bits of data, with ordinal values 0..255 (Term for bytes passed to or from a
	 non-Perl context, e.g. a disk file.)

PERL ENCODING API
       $octets	= encode(ENCODING, $string [, CHECK])
	 Encodes a string from Perl's internal form into ENCODING and returns a sequence of
	 octets.  ENCODING can be either a canonical name or an alias.	For encoding names and
	 aliases, see "Defining Aliases".  For CHECK, see "Handling Malformed Data".

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

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

	 CAVEAT: When you run "$octets = encode("utf8", $string)", then $octets may not be equal
	 to $string.  Though they both contain the same data, the utf8 flag for $octets is always
	 off.  When you encode anything, utf8 flag of the result is always off, even when it con-
	 tains completely valid utf8 string. See "The UTF-8 flag" below.

	 encode($valid_encoding, undef) is harmless but warns you for "Use of uninitialized value
	 in subroutine entry".	encode($valid_encoding, '') is harmless and warnless.

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

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

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

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

	 decode($valid_encoding, undef) is harmless but warns you for "Use of uninitialized value
	 in subroutine entry".	decode($valid_encoding, '') is harmless and warnless.

       [$length =] from_to($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 other-
	 wise.

	 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 representation so this function cannot
	 fail.

       $string = decode_utf8($octets [, CHECK]);
	 equivalent to "$string = decode("utf8", $octets [, CHECK])".  The sequence of octets
	 represented by $octets is decoded from UTF-8 into a sequence of logical characters. Not
	 all sequences of octets form valid UTF-8 encodings, so it is possible for this call to
	 fail.	For CHECK, see "Handling Malformed Data".

       Listing available encodings

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

       Returns a list of the canonical names of the available encodings that are loaded.  To get
       a list of all 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::Sup-
       ported.

       Defining Aliases

       To add a new alias to a given encoding, use:

	 use Encode;
	 use Encode::Alias;
	 define_alias(newName => ENCODING);

       After that, newName can be used as an alias for ENCODING.  ENCODING may be either the name
       of an encoding or an encoding object

       But before you do so, make sure the alias is nonexistent with "resolve_alias()", which
       returns the canonical name thereof.  i.e.

	 Encode::resolve_alias("latin1") eq "iso-8859-1" # true
	 Encode::resolve_alias("iso-8859-12")	# false; nonexistent
	 Encode::resolve_alias($name) eq $name	# true if $name is canonical

       resolve_alias() does not need "use Encode::Alias"; it can be exported via "use Encode
       qw(resolve_alias)".

       See Encode::Alias for details.

Encoding via PerlIO
       If your perl supports PerlIO (which is the default), you can use a PerlIO layer to decode
       and encode directly via a filehandle.  The following two examples are totally identical in
       their functionality.

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

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

       Unfortunately, it may be that encodings are PerlIO-savvy.  You can check if your encoding
       is supported by 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 CHECK argument is used as follows.  When you omit it, the behaviour is the same as
	 if you had passed a value of 0 for CHECK.

       CHECK = Encode::FB_DEFAULT ( == 0)
	 If CHECK is 0, (en|de)code will put a substitution character in place of a malformed
	 character.  For UCM-based encodings, <subchar> will be used.  For Unicode, the code
	 point 0xFFFD is used.	If the data is supposed to be UTF-8, an optional lexical warning
	 (category utf8) is given.

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

       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, for example because you are reading
	 with a fixed-width buffer. Here is some sample code that does exactly this:

	   my $data = ''; my $utf8 = '';
	   while(defined(read $fh, $buffer, 256)){
	     # buffer may end in a partial character so we append
	     $data .= $buffer;
	     $utf8 .= decode($encoding, $data, Encode::FB_QUIET);
	     # $data 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
	 "&#NNNN"; where NNNN is a decimal digit and XML uses "&#xHHHH"; where HHHH is the hexa-
	 decimal digit.

       The bitmask
	 These modes are actually set via a bitmask.  Here is how the FB_XX constants are laid
	 out.  You can import the FB_XX constants via "use Encode qw(:fallbacks)"; you can import
	 the generic bitmask constants via "use Encode qw(:fallback_all)".

			      FB_DEFAULT FB_CROAK FB_QUIET FB_WARN  FB_PERLQQ
	  DIE_ON_ERR	0x0001		   X
	  WARN_ON_ERR	0x0002				     X
	  RETURN_ON_ERR 0x0004			    X	     X
	  LEAVE_SRC	0x0008
	  PERLQQ	0x0100					      X
	  HTMLCREF	0x0200
	  XMLCREF	0x0400

       Unimplemented fallback schemes

       In the future, you will be able to use a code reference to a callback function for the
       value of CHECK but its API is still undecided.

       The fallback scheme does not work on EBCDIC platforms.

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-ori-
	   ented 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.

	 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 cor-
	 rected 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.

	 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 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 assue Goal #1.  And
	   with Encode Goal #2 is assumed but you still have to be careful in such cases men-
	   tioned 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 success-
	   ful, false otherwise.

	 _utf8_on(STRING)
	   [INTERNAL] Turns on the UTF-8 flag in STRING.  The data in STRING is not checked for
	   being well-formed UTF-8.  Do not use unless you know that the STRING is well-formed
	   UTF-8.  Returns the previous state of the UTF-8 flag (so please don't treat the return
	   value as indicating success or failure), or "undef" if STRING is not a string.

	 _utf8_off(STRING)
	   [INTERNAL] Turns off the UTF-8 flag in STRING.  Do not use frivolously.  Returns the
	   previous state of the UTF-8 flag (so please don't treat the return value as indicating
	   success or failure), or "undef" if STRING is not a string.

SEE ALSO
       Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding, perlebcdic, "open" in perl-
       func, 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 <danko-
       gai@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.

perl v5.8.0				    2002-06-01				      Encode(3pm)


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