Encode - character encodings in Perl
use Encode;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 encodingsEncode::Encoding Encode Implementation Base ClassEncode::Supported List of Supported EncodingsEncode::CN Simplified Chinese EncodingsEncode::JP Japanese EncodingsEncode::KR Korean EncodingsEncode::TW Traditional Chinese Encodings--------------------------------------------------------TheEncode module provides the interface between Perl strings and the rest of the system. Perl strings are sequences ofcharacters.
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 byord(S) is theUnicode codepoint for that character. The exceptions are platforms where the legacy encoding is some variant of EBCDIC rather than a superset of ASCII; seeperlebcdic.
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".
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.
Encodes the scalar valueSTRING from Perl's internal form intoENCODING 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 $octetsmight not be equal to $string. Though both contain the same data, the UTF8 flag for $octets isalways 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 isundef, thenundef is returned.
This function returns the string that results from decoding the scalar valueOCTETS, assumed to be a sequence of octets inENCODING, 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"; forCHECK, 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 $stringmight 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 isundef, thenundef is returned.
Returns theencoding object corresponding toENCODING. Returnsundef if no matchingENCODING 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-8859-1SeeEncode::Encoding for details.
Convertsin-place data between two encodings. The data in $octets must be encoded as octets andnot as characters in Perl's internal format. For example, to convert ISO-8859-1 data into Microsoft's CP1250 encoding:
from_to($octets, "iso-8859-1", "cp1250");and to convert it back:
from_to($octets, "cp1250", "iso-8859-1");Because the conversion happens in place, the data to be converted cannot be a string constant: it must be a scalar variable.
from_to() returns the length of the converted string in octets on success, andundef on error.
CAVEAT: The following operations may look the same, but are not:
from_to($data, "iso-8859-1", "utf8"); #1$data = decode("iso-8859-1", $data); #2Both #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 doesnot respect the $check during decoding. It is deliberately done that way. If you need minute control, usedecode followed byencode as follows:
$octets = encode($to, decode($from, $octets, $check_from), $check_to);Equivalent to$octets = encode("utf8", $string). The characters in $string are encoded in Perl's internal format, and the result is returned as a sequence of octets. Because all possible characters in Perl have a (loose, not strict) UTF-8 representation, this function cannot fail.
Equivalent to$string = decode("utf8", $octets [, CHECK]). The sequence of octets represented by $octets is decoded from UTF-8 into a sequence of logical characters. Because not all sequences of octets are valid UTF-8, it is quite possible for this function to fail. For CHECK, see"Handling Malformed Data".
use Encode;@list = Encode->encodings();Returns a list of canonical names of available encodings that have already been loaded. To get a list of all available encodings including those that have not yet been loaded, say:
@all_encodings = Encode->encodings(":all");Or you can give the name of a specific module:
@with_jp = Encode->encodings("Encode::JP");When "::" is not in the name, "Encode::" is assumed.
@ebcdic = Encode->encodings("EBCDIC");To find out in detail which encodings are supported by this package, seeEncode::Supported.
To add a new alias to a given encoding, use:
use Encode;use Encode::Alias;define_alias(NEWNAME => ENCODING);After that,NEWNAME can be used as an alias forENCODING. <ENCODING> may be either the name of an encoding or anencoding object.
Before you do that, first make sure the alias is nonexistent usingresolve_alias(), which returns the canonical name thereof. For example:
Encode::resolve_alias("latin1") eq "iso-8859-1" # trueEncode::resolve_alias("iso-8859-12") # false; nonexistentEncode::resolve_alias($name) eq $name # true if $name is canonicalresolve_alias() does not needuse Encode::Alias; it can be imported viause Encode qw(resolve_alias).
SeeEncode::Alias for details.
The canonical name of a given encoding does not necessarily agree with IANA Character Set Registry, commonly seen asContent-Type: text/plain; charset=WHATEVER. For most cases, the canonical name works, but sometimes it does not, most notably with "utf-8-strict".
As ofEncode version 2.21, a new methodmime_name() is thereforeadded.
use Encode;my $enc = find_encoding("UTF-8");warn $enc->name; # utf-8-strictwarn $enc->mime_name; # UTF-8See also:Encode::Encoding
If your perl supportsPerlIO (which is the default), you can use aPerlIO 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 arePerlIO-savvy. You can check to see whether your encoding is supported byPerlIO by invoking theperlio_ok method on it:
Encode::perlio_ok("hz"); # falsefind_encoding("euc-cn")->perlio_ok; # true wherever PerlIO is availableuse Encode qw(perlio_ok); # imported upon requestperlio_ok("euc-jp")Fortunately, all encodings that come withEncode core arePerlIO-savvy except for "hz" and "ISO-2022-kr". For the gory details, seeEncode::Encoding andEncode::PerlIO.
The optionalCHECK argument tellsEncode what to do when encountering malformed data. WithoutCHECK,Encode::FB_DEFAULT (== 0) is assumed.
As of version 2.12,Encode supports coderef values forCHECK; see below.
Some encodings ignoreCHECK argument. For example,Encode::Unicode ignoresCHECK and it always croaks on error.
Now here is the list ofCHECK values available
IfCHECK is 0, encoding and decoding replace any malformed character with asubstitution 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.
IfCHECK is 1, methods immediately die with an error message. Therefore, whenCHECK is 1, you should trap exceptions witheval{}, unless you really want to let itdie.
IfCHECK is set toEncode::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 calldecode 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}This is the same asFB_QUIET above, except that instead of being silent on errors, it issues a warning. This is handy for when you are debugging.
For encodings that are implemented by theEncode::XS module,CHECK==Encode::FB_PERLQQ putsencode anddecode intoperlqq fallback mode.
When you decode,\xHH is inserted for a malformed character, whereHH is the hex representation of the octet that could not be decoded to utf8. When you encode,\x{HHHH} will be inserted, whereHHHH 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; whereNNN is a decimal number, and XML uses&#xHHHH; whereHHHH is the hexadecimal number.
InEncode 2.10 or later,LEAVE_SRC is also implied.
These modes are all actually set via a bitmask. Here is how theFB_XXX constants are laid out. You can import theFB_XXX constants viause Encode qw(:fallbacks), and you can import the generic bitmask constants viause Encode qw(:fallback_all).
FB_DEFAULT FB_CROAK FB_QUIET FB_WARN FB_PERLQQDIE_ON_ERR 0x0001 XWARN_ON_ERR 0x0002 XRETURN_ON_ERR 0x0004 X XLEAVE_SRC 0x0008 XPERLQQ 0x0100 XHTMLCREF 0x0200XMLCREF 0x0400If theEncode::LEAVE_SRC bit isnot set butCHECK 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.
As ofEncode 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", $utf8, sub{ sprintf "<U+%04X>", shift });Acts likeFB_PERLQQ but U+XXXX is used instead of\x{XXXX}.
To define a new encoding, use:
use Encode qw(define_encoding);define_encoding($object, CANONICAL_NAME [, alias...]);CANONICAL_NAME will be associated with$object. The object should provide the interface described inEncode::Encoding. If more than two arguments are provided, additional arguments are considered aliases for$object.
SeeEncode::Encoding for details.
Before the introduction of Unicode support in Perl, Theeq operator just compared the strings represented by two scalars. Beginning with Perl 5.8,eq compares two strings with simultaneous consideration ofthe UTF8 flag. To explain why we made it so, I quote from page 402 ofProgramming Perl, 3rd ed.
Old byte-oriented programs should not spontaneously break on the old byte-oriented data they used to work on.
Old byte-oriented programs should magically start working on the new character-oriented data when appropriate.
Programs should run just as fast in the new character-oriented mode as in the old byte-oriented mode.
Perl should remain one language, rather than forking into a byte-oriented Perl and a character-oriented Perl.
WhenProgramming 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 howEncode handles the UTF8 flag.
When youencode, the resulting UTF8 flag is alwaysoff.
When youdecode, the resulting UTF8 flag ison--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) OFFIn ISO-8859-1 ONIn any other Encoding ON---------------------------------------------As you see, there is one exception: in ASCII. That way you can assume Goal #1. And withEncode, Goal #2 is assumed but you still have to be careful in the cases mentioned in theCAVEAT paragraphs above.
This UTF8 flag is not visible in Perl scripts, exactly for the same reason you cannot (or rather, youdon'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.
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.
[INTERNAL] Tests whether the UTF8 flag is turned on in theSTRING. IfCHECK is true, also checks whetherSTRING contains well-formed UTF-8. Returns true if successful, false otherwise.
As of Perl 5.8.1,utf8 also has theutf8::is_utf8 function.
[INTERNAL] Turns theSTRING's internal UTF8 flagon. TheSTRING isnot checked for containing only well-formed UTF-8. Do not use this unless youknow 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), orundef ifSTRING is not a string.
NOTE: For security reasons, this function does not work on tainted values.
[INTERNAL] Turns theSTRING's internal UTF8 flagoff. Do not use frivolously. Returns the previous state of the UTF8 flag, orundef ifSTRING 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.
....We now view strings not as sequences of bytes, but as sequencesof numbers in the range 0 .. 2**32-1 (or in the case of 64-bitcomputers, 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 inany 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 JSTTo: perl-unicode@perl.orgSubject: Re: Make Encode.pm support the real UTF-8Message-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 myhead.Also for what it's worth, Perl 6 will mostly default to strict butmake it easy to switch back to lax.LarryGot 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); # okayencode("UTF-8", "\x{FFFF_FFFF}", 1); # croaksIn theEncode 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 insensitivefind_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.
Encode::Encoding,Encode::Supported,Encode::PerlIO,encoding,perlebcdic,"open" in perlfunc,perlunicode,perluniintro,perlunifaq,perlunitututf8, the Perl Unicode Mailing List <perl-unicode@perl.org>
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 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.
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