| Encode - character encodings |
Encode - character encodings
use Encode;
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 --------------------------------------------------------
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 the perlebcdic manpage).
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''.
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 UTF8 flag below.
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 UTF8 flag
below.
find_encoding(ENCODING)This object is what actually does the actual (en|de)coding.
$utf8 = decode($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.
Therefore you can save time by reusing this object as follows;
my $enc = find_encoding("iso-8859-1");
while(<>){
my $utf8 = $enc->decode($_);
# and do someting with $utf8;
}
Besides ->decode and ->encode, other methods are
available as well. For instance, -> name returns the canonical
name of the encoding object.
find_encoding("latin1")->name; # iso-8859-1
See the Encode::Encoding manpage for details.
from_to($octets, "iso-8859-1", "cp1250");
and to convert it back:
from_to($octets, "cp1250", "iso-8859-1");
Note that because the conversion happens in place, the data to be converted cannot be a string constant; it must be a scalar variable.
from_to() returns the length of the converted string in octets on
success, undef on error.
CAVEAT: The following operations look the same but are not quite so;
from_to($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", $data));
See The UTF8 flag below.
Also note that
from_to($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, decode
then encode as follows;
$octets = encode($to, decode($from, $octets, $check_from), $check_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]).
The sequence of octets represented by
$octets is decoded from UTF-8 into a sequence of logical
characters. Not all sequences of octets form valid UTF-8 encodings, so
it is possible for this call to fail. For CHECK, see
Handling Malformed Data.
use Encode; @list = Encode->encodings();
Returns a list of the canonical names of the available encodings that are loaded. To get a list of all available encodings including the ones that are not loaded yet, say
@all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module.
@with_jp = Encode->encodings("Encode::JP");
When ``::'' is not in the name, ``Encode::'' is assumed.
@ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this package, see the Encode::Supported manpage.
To add a new alias to a given encoding, use:
use Encode; use Encode::Alias; define_alias(newName => ENCODING);
After that, newName can be used as an alias for ENCODING. ENCODING may be either the name of an encoding or an encoding object
But before you do so, make sure the alias is nonexistent with
resolve_alias(), which returns the canonical name thereof.
i.e.
Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexistent
Encode::resolve_alias($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 the Encode::Alias manpage for details.
The canonical name of a given encoding does not necessarily agree with
IANA IANA Character Set Registry, commonly seen as Content-Type:
text/plain; charset=I<whatever>. For most cases canonical names
work but sometimes it does not (notably 'utf-8-strict').
Therefore as of Encode version 2.21, a new method mime_name() is added.
use Encode;
my $enc = find_encoding('UTF-8');
warn $enc->name; # utf-8-strict
warn $enc->mime_name; # UTF-8
See also: the Encode::Encoding manpage
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 the Encode::Encoding manpage and the Encode::PerlIO manpage.
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.
Now here is the list of CHECK values available
0xFFFD is used. If
the data is supposed to be UTF-8, an optional lexical warning
(category utf8) is given.
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
}
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 &#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.
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 X
PERLQQ 0x0100 X
HTMLCREF 0x0200
XMLCREF 0x0400
Encode::LEAVE_SRC bit is not set, but CHECK is, then the second
argument to encode() or decode() may be assigned to by the functions. If
you're not interested in this, then bitwise-or the bitmask with it.
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", $utf8, sub{ sprintf "<U+%04X>", shift });
Acts like FB_PERLQQ but <U+XXXX> is used instead of \x{XXXX}.
To define a new encoding, use:
use Encode qw(define_encoding);
define_encoding($object, 'canonicalName' [, alias...]);
canonicalName will be associated with $object. The object should provide the interface described in the Encode::Encoding manpage. If more than two arguments are provided then additional arguments are taken as aliases for $object.
See the Encode::Encoding manpage for more details.
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 will quote page 402 of
Programming Perl, 3rd ed.
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 UTF8 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.
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 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.
The following API uses parts of Perl's internals in the current implementation. As such, they are efficient but may change.
As of perl 5.8.1, the utf8 manpage also has utf8::is_utf8().
_utf8_on(STRING)undef if STRING is not a string.
_utf8_off(STRING)undef if STRING is
not a string.
....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 narrower (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("utf_8")->name # ditto. "_" are treated as "-"
find_encoding("UTF8")->name # is 'utf8'.
The UTF8 flag is internally called UTF8, without a hyphen. It indicates whether a string is internally encoded as utf8, also without a hypen.
the Encode::Encoding manpage, the Encode::Supported manpage, the Encode::PerlIO manpage, the encoding manpage, the perlebcdic manpage, open in the perlfunc manpage, the perlunicode manpage, the perluniintro manpage, perlunifaq, perlunitut the utf8 manpage, the Perl Unicode Mailing List <perl-unicode@perl.org>
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.
While Dan Kogai retains the copyright as a maintainer, the credit should go to all those involoved. See AUTHORS for those submitted codes.
Copyright 2002-2006 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.
| Encode - character encodings |