encode(3)

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
platforms 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 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 - as 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, 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 canon ical name or an alias. For encoding names and aliases,
see "Defining Aliases". For CHECK, see "Handling Mal
formed 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 charac
ters 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 otherwise.; 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 repre
sentation so this function cannot fail.
$string = decode_utf8($octets [, CHECK]);: equivalent to "$string = decode("utf8", $octets [,
CHECK])". The sequence of octets represented by $octets
is decoded from UTF-8 into a sequence of logical charac
ters. Not all sequences of octets form valid UTF-8
encodings, so it is possible for this call to fail. For
CHECK, see "Handling Malformed Data".
Listing available encodings: use Encode;
@list = Encode->encodings();
Returns a list of the canonical names of the available encodings that are loaded. To get a list of all available encodings including the ones that are not loaded yet, say: @all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module.: @with_jp = Encode->encodings("Encode::JP");
When "::" is not in the name, "Encode::" is assumed.: @ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this package, see Encode::Supported.
Defining Aliases
To add a new alias to a given encoding, use:: use Encode;
use Encode::Alias;
define_alias(newName => ENCODING);
After that, newName can be used as an alias for ENCODING. ENCODING may be either the name of an encoding or an encoding object
But before you do so, make sure the alias is nonexistent with "resolve_alias()", which returns the canonical name thereof. i.e.: Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexis; tent
Encode::resolve_alias($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 iden tical 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 re; quest
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 char_ acter 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 charac

ter

}; 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, "" 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, "HHH}" 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 "HHH}", HTML uses "&#NNNN"; where NNNN
is a decimal digit and XML uses "&#xHHHH"; where HHHH is
the hexadecimal 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::Encod ing. If more than two arguments are provided then addi tional 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 appro
priate.; Goal #3:
Programs should run just as fast in the new characteroriented 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 charac
ter-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 assue 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 float
ing 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 successful, 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.

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.

docs.sk

comprehensive documentation repository

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