Manpages - Encode_Supported.3perl

Encode::Supported – Encodings supported by Encode

As of Perl 5.8.0, at least the following encodings are recognized. Note that unless otherwise specified, they are all case insensitive (via alias) and all occurrence of spaces are replaced with ’-’. In other words, ISO 8859 1 and iso-8859-1 are identical.

Encodings are categorized and implemented in several different modules but you don’t have to use Encode::XX to make them available for most cases. Encode.pm will automatically load those modules on demand.

The following encodings are not supported as yet; some because they are rarely used, some because of technical difficulties. They may be supported by external modules via CPAN in the future, however.

ISO-2022-JP-2 [RFC1554]

Not very popular yet. Needs Unicode Database or equivalent to implement encode() (because it includes JIS X 0208/0212, KSC5601, and GB2312 simultaneously, whose code points in Unicode overlap. So you need to lookup the database to determine to what character set a given Unicode character should belong).

ISO-2022-CN [RFC1922]

Not very popular. Needs CNS 11643-1 and -2 which are not available in this module. CNS 11643 is supported (via euc-tw) in Encode::HanExtra. Audrey Tang may add support for this encoding in her module in future.

Various HP-UX encodings

The following are unsupported due to the lack of mapping data. 8 - arabic8, greek8, hebrew8, kana8, thai8, and turkish8 15 - japanese15, korean15, and roi15

Cyrillic encoding ISO-IR-111

Anton Tagunov doubts its usefulness.

ISO-8859-8-1 [Hebrew]

None of the Encode team knows Hebrew enough (ISO-8859-8, cp1255 and MacHebrew are supported because and just because there were mappings available at http://www.unicode.org/). Contributions welcome.

ISIRI 3342, Iran System, ISIRI 2900 [Farsi]

Ditto.

Thai encoding TCVN

Ditto.

Vietnamese encodings VPS

Though Jungshik Shin has reported that Mozilla supports this encoding, it was too late before 5.8.0 for us to add it. In the future, it may be available via a separate module. See http://lxr.mozilla.org/seamonkey/source/intl/uconv/ucvlatin/vps.uf and http://lxr.mozilla.org/seamonkey/source/intl/uconv/ucvlatin/vps.ut if you are interested in helping us.

Various Mac encodings

The following are unsupported due to the lack of mapping data. MacArmenian, MacBengali, MacBurmese, MacEthiopic MacExtArabic, MacGeorgian, MacKannada, MacKhmer MacLaotian, MacMalayalam, MacMongolian, MacOriya MacSinhalese, MacTamil, MacTelugu, MacTibetan MacVietnamese The rest which are already available are based upon the vendor mappings at http://www.unicode.org/Public/MAPPINGS/VENDORS/APPLE/ .

(Mac) Indic encodings

The maps for the following are available at http://www.unicode.org/ but remain unsupported because those encodings need an algorithmical approach, currently unsupported by enc2xs: MacDevanagari MacGurmukhi MacGujarati For details, please see Unicode mapping issues and notes: at http://www.unicode.org/Public/MAPPINGS/VENDORS/APPLE/DEVANAGA.TXT . I believe this issue is prevalent not only for Mac Indics but also in other Indic encodings, but the above were the only Indic encodings maps that I could find at http://www.unicode.org/ .

We are used to using the term (character) encoding and character set interchangeably. But just as confusing the terms byte and character is dangerous and the terms should be differentiated when needed, we need to differentiate encoding and character set.

To understand that, here is a description of how we make computers grok our characters.

• First we start with which characters to include. We call this collection of characters character repertoire.
• Then we have to give each character a unique ID so your computer can tell the difference between ’a’ and ’A’. This itemized character repertoire is now a character set.
• If your computer can grow the character set without further processing, you can go ahead and use it. This is called a coded character set (CCS) or raw character encoding. ASCII is used this way for most cases.
• But in many cases, especially multi-byte CJK encodings, you have to tweak a little more. Your network connection may not accept any data with the Most Significant Bit set, and your computer may not be able to tell if a given byte is a whole character or just half of it. So you have to encode the character set to use it. A character encoding scheme (CES) determines how to encode a given character set, or a set of multiple character sets. 7bit ISO-2022 is an example of a CES. You switch between character sets via escape sequences.

Technically, or mathematically, speaking, a character set encoded in such a CES that maps character by character may form a CCS. EUC is such an example. The CES of EUC is as follows:

• Map ASCII unchanged.
• Map such a character set that consists of 94 or 96 powered by N members by adding 0x80 to each byte.
• You can also use 0x8e and 0x8f to indicate that the following sequence of characters belongs to yet another character set. To each following byte is added the value 0x80.

By carefully looking at the encoded byte sequence, you can find that the byte sequence conforms a unique number. In that sense, EUC is a CCS generated by a CES above from up to four CCS (complicated?). UTF-8 falls into this category. See UTF-8 in perlUnicode to find out how UTF-8 maps Unicode to a byte sequence.

You may also have found out by now why 7bit ISO-2022 cannot comprise a CCS. If you look at a byte sequence \x21\x21, you can’t tell if it is two !’s or IDEOGRAPHIC SPACE. EUC maps the latter to \xA1\xA1 so you have no trouble differentiating between !!. and .

This section tries to classify the supported encodings by their applicability for information exchange over the Internet and to choose the most suitable aliases to name them in the context of such communication.

• To (en|de)code encodings marked by (**), you need Encode::HanExtra, available from CPAN.

Encoding names

US-ASCII UTF-8 ISO-8859-* KOI8-R Shift_JIS EUC-JP ISO-2022-JP ISO-2022-JP-1 EUC-KR Big5 GB2312

are registered with IANA as preferred MIME names and may be used over the Internet.

Shift_JIS has been officialized by JIS X 0208:1997. Microsoft-related naming mess gives details.

GB2312 is the IANA name for EUC-CN. See Microsoft-related naming mess for details.

GB_2312-80 raw encoding is available as gb2312-raw with Encode. See Encode::CN for details.

EUC-CN KOI8-U [RFC2319]

have not been registered with IANA (as of March 2002) but seem to be supported by major web browsers. The IANA name for EUC-CN is GB2312.

KS_C_5601-1987

is heavily misused. See Microsoft-related naming mess for details.

KS_C_5601-1987 raw encoding is available as kcs5601-raw with Encode. See Encode::KR for details.

UTF-16 UTF-16BE UTF-16LE

are IANA-registered =charset=s. See [RFC 2781] for details. Jungshik Shin reports that UTF-16 with a BOM is well accepted by MS IE 5/6 and NS 4/6. Beware however that

• UTF-16 support in any software you’re going to be using/interoperating with has probably been less tested then UTF-8 support
• UTF-8 coded data seamlessly passes traditional command piping (cat, more, etc.) while UTF-16 coded data is likely to cause confusion (with its zero bytes, for example)
• it is beyond the power of words to describe the way HTML browsers encode non-ASCII form data. To get a general impression, visit http://www.alanflavell.org.uk/charset/form-i18n.html. While encoding of form data has stabilized for UTF-8 encoded pages (at least IE 5/6, NS 6, and Opera 6 behave consistently), be sure to expect fun (and cross-browser discrepancies) with UTF-16 encoded pages!

The rule of thumb is to use UTF-8 unless you know what you’re doing and unless you really benefit from using UTF-16.

ISO-IR-165 [RFC1345] VISCII GB 12345 GB 18030 () (see links below) EUC-TW ()

are totally valid encodings but not registered at IANA. The names under which they are listed here are probably the most widely-known names for these encodings and are recommended names.

BIG5PLUS (**)

is a proprietary name.

character repertoire

A collection of unique characters. A character set in the strictest sense. At this stage, characters are not numbered.

coded character set (CCS)

A character set that is mapped in a way computers can use directly. Many character encodings, including EUC, fall in this category.

character encoding scheme (CES)

An algorithm to map a character set to a byte sequence. You don’t have to be able to tell which character set a given byte sequence belongs. 7-bit ISO-2022 is a CES but it cannot be a CCS. EUC is an example of being both a CCS and CES.

charset (in MIME context)

has long been used in the meaning of encoding, CES. While the word combination character set has lost this meaning in MIME context since [RFC 2130], the charset abbreviation has retained it. This is how [RFC 2277] and [RFC 2278] bless charset: This document uses the term “charset” to mean a set of rules for mapping from a sequence of octets to a sequence of characters, such as the combination of a coded character set and a character encoding scheme; this is also what is used as an identifier in MIME “charset=” parameters, and registered in the IANA charset registry … (Note that this is NOT a term used by other standards bodies, such as ISO). [RFC 2277]

EUC

Extended Unix Character. See ISO-2022.

ISO-2022

A CES that was carefully designed to coexist with ASCII. There are a 7 bit version and an 8 bit version. The 7 bit version switches character set via escape sequence so it cannot form a CCS. Since this is more difficult to handle in programs than the 8 bit version, the 7 bit version is not very popular except for iso-2022-jp, the de facto standard CES for e-mails. The 8 bit version can form a CCS. EUC and ISO-8859 are two examples thereof. Pre-5.6 perl could use them as string literals.

UCS

Short for Universal Character Set. When you say just UCS, it means Unicode.

UCS-2

ISO/IEC 10646 encoding form: Universal Character Set coded in two octets.

Unicode

A character set that aims to include all character repertoires of the world. Many character sets in various national as well as industrial standards have become, in a way, just subsets of Unicode.

UTF

Short for Unicode Transformation Format. Determines how to map a Unicode character into a byte sequence.

UTF-16

A UTF in 16-bit encoding. Can either be in big endian or little endian. The big endian version is called UTF-16BE (equal to UCS-2 + surrogate support) and the little endian version is called UTF-16LE.

Encode, Encode::Byte, Encode::CN, Encode::JP, Encode::KR, Encode::TW, Encode::EBCDIC, Encode::Symbol Encode::MIME::Header, Encode::Guess

ECMA

European Computer Manufacturers Association http://www.ecma.ch

• ECMA-035 (eq “ISO-2022”) :: http://www.ecma.ch/ecma1/STAND/ECMA-035.HTM The specification of ISO-2022 is available from the link above.

IANA

Internet Assigned Numbers Authority http://www.iana.org/

• Assigned Charset Names by IANA :: http://www.iana.org/assignments/character-sets Most of the canonical names in Encode derive from this list so you can directly apply the string you have extracted from MIME header of mails and web pages.

ISO

International Organization for Standardization http://www.iso.ch/

RFC

Request For Comments Ω- need I say more? http://www.rfc-editor.org/, http://www.ietf.org/rfc.html, http://www.faqs.org/rfcs/

UC

Unicode Consortium http://www.unicode.org/

Unicode Glossary

http://www.unicode.org/glossary/ The glossary of this document is based upon this site.