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 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 -------------------------------------------------------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 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 Consor-tium. Consortium.
tium. On most platforms the ordinal values of the characters (as returned by "ord(ch)") is the "Uni-code "Unicode
code 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 con-text, context,
text, 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. ENCOD-ING ENCODING
ING 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 contains completely valid utf8
string. See "The UTF-8 flag" below.
If the $string is "undef" then "undef" is returned.
$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 encod-ing encoding
ing 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.
If the $string is "undef" then "undef" is returned.
[$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($octets, "cp1250", "iso-8859-1");
Note that because the conversion happens in place, the data to be converted cannot be a string con-stant; constant;
stant; it must be a scalar variable.
from_to() returns the length of the converted string in octets on success, undef on error.
CAVEAT: The following operations look the same but are not quite so;
from_to($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 charac-ters characters
ters 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
$octets is decoded from UTF-8 into a sequence of logical characters. Not all sequences of octets
form valid UTF-8 encodings, so it is possible for this call to fail. For CHECK, see "Handling Mal-formed Malformed
formed Data".
Listing available encodings
use Encode;
@list = Encode->encodings();
Returns a list of the canonical names of the available encodings that are loaded. To get a list of
all available encodings including the ones that are not loaded yet, say
@all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module.
@with_jp = Encode->encodings("Encode::JP");
When "::" is not in the name, "Encode::" is assumed.
@ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this package, see Encode::Supported.
Defining Aliases
To add a new alias to a given encoding, use:
use Encode;
use Encode::Alias;
define_alias(newName => ENCODING);
After that, newName can be used as an alias for ENCODING. ENCODING may be either the name of an
encoding or an encoding object
But before you do so, make sure the alias is nonexistent with "resolve_alias()", which returns the
canonical name thereof. i.e.
Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexistent
Encode::resolve_alias($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 sup-ported supported
ported 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 optional CHECK argument tells Encode what to do when it encounters 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, (en|de)code will put a substitution character in place of a malformed character.
When you encode, <subchar> will be used. When you decode 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 error with eval{} unless you really want to let it die.
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 charac-ter character
ter sequences, (i.e. you are reading with a fixed-width buffer). Here is a sample code that does
exactly this:
my $buffer = ''; my $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 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 representa-tion representation
tion 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 "&#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 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 con-stants constants
stants 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
coderef for CHECK
As of Encode 2.12 CHECK can also be a code reference which takes the ord value of 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, '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 $object.
See Encode::Encoding for more details.
The UTF-8 flag
Before the introduction of utf8 support in perl, The "eq" operator just compared the strings repre-sented represented
sented by two scalars. Beginning with perl 5.8, "eq" compares two strings with simultaneous consider-ation consideration
ation of the utf8 flag. To explain why we made it so, I will quote page 402 of "Programming Perl, 3rd
ed."
Goal #1:
Old byte-oriented programs should not spontaneously break on the old byte-oriented data they used
to work on.
Goal #2:
Old byte-oriented programs should magically start working on the new character-oriented data when
appropriate.
Goal #3:
Programs should run just as fast in the new character-oriented mode as in the old byte-oriented
mode.
Goal #4:
Perl should remain one language, rather than forking into a byte-oriented Perl and a character-ori-ented character-oriented
ented Perl.
Back when "Programming Perl, 3rd ed." was written, not even Perl 5.6.0 was born and many features
documented in the book remained unimplemented for a long time. Perl 5.8 corrected this and the
introduction of the UTF-8 flag is one of them. You can think of this perl notion as of a byte-ori-ented byte-oriented
ented mode (utf8 flag off) and a character-oriented mode (utf8 flag on).
Here is how Encode takes care of the utf8 flag.
When you encode, the resulting utf8 flag is always off.
When you decode, the resulting utf8 flag is on unless you can unambiguously represent data. Here
is the definition of dis-ambiguity.
After "$utf8 = decode('foo', $octet);",
When $octet is... The utf8 flag in $utf8 is
---------------------------------------------In --------------------------------------------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 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 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 successful, false otherwise.
As of perl 5.8.1, utf8 also has utf8::is_utf8().
_utf8_on(STRING)
[INTERNAL] Turns on the UTF-8 flag in STRING. The data in STRING is not checked for being well-formed wellformed
formed UTF-8. Do not use unless you know that the STRING is well-formed UTF-8. Returns the previ-ous previous
ous state of the UTF-8 flag (so please don't treat the return value as indicating success or fail-ure), failure),
ure), 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.
UTF-8 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 been the perl's notion of UTF-8 but official UTF-8 is more strict; Its ranges is much nar-rower narrower
rower (0 .. 10FFFF), some sequences are not allowed (i.e. Those used in the surrogate pair, 0xFFFE,
et al).
Now that is overruled by Larry Wall himself.
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
Do you copy? As of Perl 5.8.7, UTF-8 means strict, official UTF-8 while utf8 means liberal, lax,
version thereof. And Encode version 2.10 or later thus groks the difference between "UTF-8" and
C"utf8".
encode("utf8", "\x{FFFF_FFFF}", 1); # okay
encode("UTF-8", "\x{FFFF_FFFF}", 1); # croaks
"UTF-8" in Encode is actually a canonical name for "utf-8-strict". Yes, the hyphen between "UTF" and
"8" is important. Without it Encode goes "liberal"
find_encoding("UTF-8")->name # is 'utf-8-strict'
find_encoding("utf-8")->name # ditto. names are case insensitive
find_encoding("utf8")->name # ditto. "_" are treated as "-"
find_encoding("UTF8")->name # is 'utf8'.
SEE ALSO
Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding, perlebcdic, "open" in perlfunc, perlu-nicode, perlunicode,
nicode, 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-uni-
code@perl.org> so we can all share.
perl v5.8.8 2001-09-21 Encode(3pm)
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