|UTF-8(7)||Linux Programmer's Manual||UTF-8(7)|
The UTF-8 encoding of Unicode and UCS does not have these problems and is the common way in which Unicode is used on UNIX-style operating systems.
The xxx bit positions are filled with the bits of the character code number in binary representation, most significant bit first (big-endian). Only the shortest possible multibyte sequence which can represent the code number of the character can be used.
The UCS code values 0xd800–0xdfff (UTF-16 surrogates) as well as 0xfffe and 0xffff (UCS noncharacters) should not appear in conforming UTF-8 streams. According to RFC 3629 no point above U+10FFFF should be used, which limits characters to four bytes.
and character 0x2260 = 0010 0010 0110 0000 (the "not equal" symbol) is encoded as:
in order to activate the UTF-8 support in applications.
Application software that has to be aware of the used character encoding should always set the locale with for example
and programmers can then test the expression
to determine whether a UTF-8 locale has been selected and whether therefore all plaintext standard input and output, terminal communication, plaintext file content, filenames and environment variables are encoded in UTF-8.
Programmers accustomed to single-byte encodings such as US-ASCII or ISO 8859 have to be aware that two assumptions made so far are no longer valid in UTF-8 locales. Firstly, a single byte does not necessarily correspond any more to a single character. Secondly, since modern terminal emulators in UTF-8 mode also support Chinese, Japanese, and Korean double-width characters as well as nonspacing combining characters, outputting a single character does not necessarily advance the cursor by one position as it did in ASCII. Library functions such as mbsrtowcs(3) and wcswidth(3) should be used today to count characters and cursor positions.
The official ESC sequence to switch from an ISO 2022 encoding scheme (as used for instance by VT100 terminals) to UTF-8 is ESC % G ("\x1b%G"). The corresponding return sequence from UTF-8 to ISO 2022 is ESC % @ ("\x1b%@"). Other ISO 2022 sequences (such as for switching the G0 and G1 sets) are not applicable in UTF-8 mode.