{ "mode": "man", "parameter": "unicode", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/unicode/7/json", "generated": "2026-06-03T02:31:44Z", "sections": { "NAME": { "content": "unicode - universal character set\n", "subsections": [] }, "DESCRIPTION": { "content": "The international standard ISO 10646 defines the Universal Character Set (UCS). UCS contains\nall characters of all other character set standards. It also guarantees \"round-trip compati‐\nbility\"; in other words, conversion tables can be built such that no information is lost when\na string is converted from any other encoding to UCS and back.\n\nUCS contains the characters required to represent practically all known languages. This in‐\ncludes not only the Latin, Greek, Cyrillic, Hebrew, Arabic, Armenian, and Georgian scripts,\nbut also Chinese, Japanese and Korean Han ideographs as well as scripts such as Hiragana,\nKatakana, Hangul, Devanagari, Bengali, Gurmukhi, Gujarati, Oriya, Tamil, Telugu, Kannada, Ma‐\nlayalam, Thai, Lao, Khmer, Bopomofo, Tibetan, Runic, Ethiopic, Canadian Syllabics, Cherokee,\nMongolian, Ogham, Myanmar, Sinhala, Thaana, Yi, and others. For scripts not yet covered, re‐\nsearch on how to best encode them for computer usage is still going on and they will be added\neventually. This might eventually include not only Hieroglyphs and various historic Indo-Eu‐\nropean languages, but even some selected artistic scripts such as Tengwar, Cirth, and Klin‐\ngon. UCS also covers a large number of graphical, typographical, mathematical, and scien‐\ntific symbols, including those provided by TeX, Postscript, APL, MS-DOS, MS-Windows, Macin‐\ntosh, OCR fonts, as well as many word processing and publishing systems, and more are being\nadded.\n\nThe UCS standard (ISO 10646) describes a 31-bit character set architecture consisting of 128\n24-bit groups, each divided into 256 16-bit planes made up of 256 8-bit rows with 256 column\npositions, one for each character. Part 1 of the standard (ISO 10646-1) defines the first\n65534 code positions (0x0000 to 0xfffd), which form the Basic Multilingual Plane (BMP), that\nis plane 0 in group 0. Part 2 of the standard (ISO 10646-2) adds characters to group 0 out‐\nside the BMP in several supplementary planes in the range 0x10000 to 0x10ffff. There are no\nplans to add characters beyond 0x10ffff to the standard, therefore of the entire code space,\nonly a small fraction of group 0 will ever be actually used in the foreseeable future. The\nBMP contains all characters found in the commonly used other character sets. The supplemen‐\ntal planes added by ISO 10646-2 cover only more exotic characters for special scientific,\ndictionary printing, publishing industry, higher-level protocol and enthusiast needs.\n\nThe representation of each UCS character as a 2-byte word is referred to as the UCS-2 form\n(only for BMP characters), whereas UCS-4 is the representation of each character by a 4-byte\nword. In addition, there exist two encoding forms UTF-8 for backward compatibility with\nASCII processing software and UTF-16 for the backward-compatible handling of non-BMP charac‐\nters up to 0x10ffff by UCS-2 software.\n\nThe UCS characters 0x0000 to 0x007f are identical to those of the classic US-ASCII character\nset and the characters in the range 0x0000 to 0x00ff are identical to those in ISO 8859-1\n(Latin-1).\n", "subsections": [ { "name": "Combining characters", "content": "Some code points in UCS have been assigned to combining characters. These are similar to the\nnonspacing accent keys on a typewriter. A combining character just adds an accent to the\nprevious character. The most important accented characters have codes of their own in UCS,\nhowever, the combining character mechanism allows us to add accents and other diacritical\nmarks to any character. The combining characters always follow the character which they mod‐\nify. For example, the German character Umlaut-A (\"Latin capital letter A with diaeresis\")\ncan either be represented by the precomposed UCS code 0x00c4, or alternatively as the combi‐\nnation of a normal \"Latin capital letter A\" followed by a \"combining diaeresis\": 0x0041\n0x0308.\n\nCombining characters are essential for instance for encoding the Thai script or for mathemat‐\nical typesetting and users of the International Phonetic Alphabet.\n" }, { "name": "Implementation levels", "content": "As not all systems are expected to support advanced mechanisms like combining characters, ISO\n10646-1 specifies the following three implementation levels of UCS:\n\nLevel 1 Combining characters and Hangul Jamo (a variant encoding of the Korean script, where\na Hangul syllable glyph is coded as a triplet or pair of vowel/consonant codes) are\nnot supported.\n\nLevel 2 In addition to level 1, combining characters are now allowed for some languages\nwhere they are essential (e.g., Thai, Lao, Hebrew, Arabic, Devanagari, Malayalam).\n\nLevel 3 All UCS characters are supported.\n\nThe Unicode 3.0 Standard published by the Unicode Consortium contains exactly the UCS Basic\nMultilingual Plane at implementation level 3, as described in ISO 10646-1:2000. Unicode 3.1\nadded the supplemental planes of ISO 10646-2. The Unicode standard and technical reports\npublished by the Unicode Consortium provide much additional information on the semantics and\nrecommended usages of various characters. They provide guidelines and algorithms for edit‐\ning, sorting, comparing, normalizing, converting, and displaying Unicode strings.\n" }, { "name": "Unicode under Linux", "content": "Under GNU/Linux, the C type wchart is a signed 32-bit integer type. Its values are always\ninterpreted by the C library as UCS code values (in all locales), a convention that is sig‐\nnaled by the GNU C library to applications by defining the constant STDCISO10646 as\nspecified in the ISO C99 standard.\n\nUCS/Unicode can be used just like ASCII in input/output streams, terminal communication,\nplaintext files, filenames, and environment variables in the ASCII compatible UTF-8 multibyte\nencoding. To signal the use of UTF-8 as the character encoding to all applications, a suit‐\nable locale has to be selected via environment variables (e.g., \"LANG=enGB.UTF-8\").\n\nThe nllanginfo(CODESET) function returns the name of the selected encoding. Library func‐\ntions such as wctomb(3) and mbsrtowcs(3) can be used to transform the internal wchart char‐\nacters and strings into the system character encoding and back and wcwidth(3) tells, how many\npositions (0–2) the cursor is advanced by the output of a character.\n" }, { "name": "Private Use Areas (PUA)", "content": "In the Basic Multilingual Plane, the range 0xe000 to 0xf8ff will never be assigned to any\ncharacters by the standard and is reserved for private usage. For the Linux community, this\nprivate area has been subdivided further into the range 0xe000 to 0xefff which can be used\nindividually by any end-user and the Linux zone in the range 0xf000 to 0xf8ff where exten‐\nsions are coordinated among all Linux users. The registry of the characters assigned to the\nLinux zone is maintained by LANANA and the registry itself is Documentation/admin-guide/uni‐\ncode.rst in the Linux kernel sources (or Documentation/unicode.txt before Linux 4.10).\n\nTwo other planes are reserved for private usage, plane 15 (Supplementary Private Use Area-A,\nrange 0xf0000 to 0xffffd) and plane 16 (Supplementary Private Use Area-B, range 0x100000 to\n0x10fffd).\n" }, { "name": "Literature", "content": "* Information technology — Universal Multiple-Octet Coded Character Set (UCS) — Part 1: Ar‐\nchitecture and Basic Multilingual Plane. International Standard ISO/IEC 10646-1, Interna‐\ntional Organization for Standardization, Geneva, 2000.\n\nThis is the official specification of UCS . Available from ⟨http://www.iso.ch/⟩.\n\n* The Unicode Standard, Version 3.0. The Unicode Consortium, Addison-Wesley, Reading, MA,\n2000, ISBN 0-201-61633-5.\n\n* S. Harbison, G. Steele. C: A Reference Manual. Fourth edition, Prentice Hall, Englewood\nCliffs, 1995, ISBN 0-13-326224-3.\n\nA good reference book about the C programming language. The fourth edition covers the\n1994 Amendment 1 to the ISO C90 standard, which adds a large number of new C library func‐\ntions for handling wide and multibyte character encodings, but it does not yet cover ISO\nC99, which improved wide and multibyte character support even further.\n\n* Unicode Technical Reports.\n⟨http://www.unicode.org/reports/⟩\n\n* Markus Kuhn: UTF-8 and Unicode FAQ for UNIX/Linux.\n⟨http://www.cl.cam.ac.uk/~mgk25/unicode.html⟩\n\n* Bruno Haible: Unicode HOWTO.\n⟨http://www.tldp.org/HOWTO/Unicode-HOWTO.html⟩\n" } ] }, "SEE ALSO": { "content": "locale(1), setlocale(3), charsets(7), utf-8(7)\n", "subsections": [] }, "COLOPHON": { "content": "This page is part of release 5.10 of the Linux man-pages project. A description of the\nproject, information about reporting bugs, and the latest version of this page, can be found\nat https://www.kernel.org/doc/man-pages/.\n\n\n\nGNU 2020-08-13 UNICODE(7)", "subsections": [] } }, "summary": "unicode - universal character set", "flags": [], "examples": [], "see_also": [ { "name": "locale", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/locale/1/json" }, { "name": "setlocale", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/setlocale/3/json" }, { "name": "charsets", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/charsets/7/json" }, { "name": "utf-8", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/utf-8/7/json" } ] }