UTF-8

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UTF-8 是一种可变长度的字符编码，在本例中，这意味着它每个符号使用 1 到 4 个字节。因此，第一个 UTF-8 字节用于编码 ASCII，使字符集与 ASCII 完全向后兼容。 UTF-8 意味着 ASCII 和拉丁字符可以互换，数据大小几乎没有增加，因为只使用第一个字节。被分配了更高字节范围的东方字母（如日语）用户就不会那么幸福了，因为这会导致他们的数据有多达 50% 的冗余。

字符编码

什么是字符编码？

计算机本身并不像人类那样理解印刷文本。对于计算机，文本的每个字符都由一个数字表示。传统上，用于表示字母和字符的每组数字（称为编码系统、编码或字符集）的大小都受到计算机硬件限制。

字符编码的历史

最常见（或至少是最广泛接受的）字符集是 ASCII（美国信息交换标准代码）。人们普遍认为 ASCII 是有史以来最成功的软件标准。现代 ASCII 于 1986 年由美国国家标准协会标准化（ANSI X3.4, RFC 20, ISO/IEC 646:1991, ECMA-6）。

ASCII 是严格的七位，这意味着它使用可以用七位二进制数字表示的位模式，它提供 0 到 127 的十进制范围。其中包括 32 个不可见的控制字符，大多数在 0 到 31 之间，最后一个控制字符 DEL 或删除位于 127。字符 32 到 126 是可见字符：空格、标点符号、拉丁字母和数字。

ASCII 中的第 8 位最初用作错误检查的奇偶校验位。如果不需要错误检查，则保留为 0。这意味着，对于 ASCII，每个字符都由一个字节表示。

Although ASCII was enough for communication in modern English, in other European languages that include accented characters, things were not so easy. The ISO 8859 standards were developed to meet these needs. They were backwards compatible with ASCII, but instead of leaving the eighth bit blank, they used it to allow another 128 characters (32 controls plus 96 visible characters) in each encoding. ISO 8859's limitations soon came to light, and there are currently 15 variants of the ISO 8859 standard (8859-1 through to 8859-15). Outside of the ASCII-compatible byte range of these character sets, there is often conflict between the letters represented by each byte. To complicate interoperability between character encodings further, Windows-1252 is used in some versions of Microsoft Windows instead for Western European languages. Its visible characters are a super-set of ISO 8859-1, however it is different in several ways; these sets do all retain ASCII compatibility.

The necessary development of completely different single-byte encodings for non-Latin alphabets, such as EUC (Extended Unix Coding) which is used for Japanese and Korean (and to a lesser extent Chinese) created more confusion. Other operating systems still used different character sets for the same languages, for example, Shift-JIS and ISO-2022-JP. Users wishing to view Cyrillic glyphs had to choose between KOI8-R for Russian and Bulgarian or KOI8-U for Ukrainian, as well as all the other Cyrillic encodings such as the unsuccessful ISO 8859-5, and the common Windows-1251 set. All of these character sets broke most compatibility with ASCII. Although it should be mentioned KOI8 encodings place Cyrillic characters in Latin order, so in case the eighth bit is stripped, text is still decipherable on an ASCII terminal through case-reversed transliteration.

All of this has led to mass confusion, and to an almost total inability for multilingual communication; especially across different alphabets. Enter Unicode.

什么是 Unicode?

Unicode 抛弃了传统的单字节字符集限制。它使用 65536 个码位的 17 个“平面（plane）”来描述最多 1114112 个字符。作为第一个平面，又名“基本多文种平面”或 BMP，几乎包含用户需要的所有字符。许多人错误地认为 Unicode 是 16 位字符集。

Unicode 有多种不同的映射方式，但最常见的两种是 UTF（Unicode 转换格式）和 UCS（通用字符集）。 UTF 后面的数字表示一个单位的位数，UCS 后面的数字表示字节数。 UTF-8 由于其 8-bit clean 的特性，已成为 Unicode 文本交换最普遍的方式；因此，这是本文档的主题。

UTF-8 能做什么

UTF-8 allows users to work in a standards-compliant and internationally accepted multilingual environment, with a comparatively low data redundancy. It is the preferred way for transmitting non-ASCII characters over the Internet, through Email, IRC, or almost any other medium. Despite this, many people regard UTF-8 in online communication as abusive. It is always best to be aware of the attitude towards UTF-8 in a specific channel, mailing list, or Usenet group before using non-ASCII UTF-8.

在 Gentoo 中设置 UTF-8

查找或创建 UTF-8 语言环境

既然 Unicode 背后的原理已经阐述完毕，接下来就可以在本地开始使用 UTF-8 了！

对更多知识感兴趣的用户可以在 Gentoo 本地化指南中找到进一步的解释。

接下来，用户需要决定 UTF-8 语言环境是否可用于选择的语言，或者是否需要生成一个。

user $locale -a | grep 'en_GB'
en_GB
en_GB.utf8

From the output of the above command, look for a result with a suffix similar to .UTF-8. If there is no result with a similar suffix a UTF-8 compatible locale must be created.

The command lists the suffix in lower case without any hyphens, glibc understands both forms of the suffix, many other programs don't. The most common example of which is Xorg. So it is best to always use UTF-8 in preference to utf8.

附注
Only execute the following code if the system does not have a UTF-8 locale available for the language of choice.

Replace "en_GB" with the desired locale setting:

root #localedef -i en_GB -f UTF-8 en_GB.UTF-8

Another way to include a UTF-8 locale is to add it to the /etc/locale.gen file and generate necessary locales using the locale-gen command. Locales will be written to the locale-archive /usr/lib/locale/locale-archive.

代码 Line in /etc/locale.gen
en_GB.UTF-8 UTF-8
root #locale-gen
 * Generating 1 locales (this might take a while) with 1 jobs
 *  (1/1) Generating en_GB.UTF-8 ...                            [ ok ]
 * Generation complete

设定 locale

There is one environment variable that needs to be set in order to use the new UTF-8 locales: LC_CTYPE (optionally modify the LANG variable to change the system language as well). There are also many different ways to set it; some system administrators prefer to only have a UTF-8 environment for a specific user, in which case they set them in their ~/.profile (/bin/sh for Bourne shell users), ~/.bash_profile or ~/.bashrc (/bin/bash for Bourne again shell users). More details and best practices can be found in the Localization Guide.

Still others prefer to set the locale globally. One specific circumstance where the author particularly recommends doing this is when /etc/init.d/xdm is in use, because this init script starts the display manager and desktop before any of the aforementioned shell startup files are sourced. In other words, this is performed before any of the variables are loaded in the environment.

Setting the locale globally should be done using /etc/env.d/02locale file. This file should look something like the following:

文件 /etc/env.d/02localeDemonstration of en_GB.UTF-8
## (As always, change "en_GB.UTF-8" to the appropriate locale value; each language has a different value!)
LANG="en_GB.UTF-8"
附注
It is possible to substitute the LC_CTYPE variable for the LANG variable. For more information on the categories affected by using LC_CTYPE read the GNU locale page.

Next, the environment must be updated by running the following command:

root #env-update
>>> Regenerating /etc/ld.so.cache...
root #source /etc/profile

Now, run locale with no arguments to see if the correct variables have been loaded in the environment:

root #locale
LANG=en_GB.utf8
LC_CTYPE="en_GB.utf8"
LC_NUMERIC="en_GB.utf8"
LC_TIME="en_GB.utf8"
LC_COLLATE="en_GB.utf8"
LC_MONETARY="en_GB.utf8"
LC_MESSAGES="en_GB.utf8"
LC_PAPER="en_GB.utf8"
LC_NAME="en_GB.utf8"
LC_ADDRESS="en_GB.utf8"
LC_TELEPHONE="en_GB.utf8"
LC_MEASUREMENT="en_GB.utf8"
LC_IDENTIFICATION="en_GB.utf8"
LC_ALL=

The values of locale environment variables that have been explicitly set e.g. in an export statement (if using bash) are listed without double quotes. Those whose value has been inherited from other locale environment variables have their values in double quotes.

Alternative: Using eselect to set locales

Although it is good to maintain the system as described above, it is possible to verify the correct locale configured using the eselect utility.

Use eselect to list the available locales on the system:

root #eselect locale list 
  [1] C
  [2] POSIX *
  [3] en_GB.utf8
  [ ] (free form)

Using eselect setting the locale is as simple as listing them. Once the correct locale has been determined invoke:

root #eselect locale set 3 
Setting LANG to en_GB.utf8 ...

Check the result:

root #eselect locale list 
  [1] C
  [2] POSIX
  [3] en_GB.utf8 *
  [ ] (free form)

In case it is preferred to have /etc/env.d/02locale with .UTF-8 instead of .utf8, run the appropriate eselect command:

root #eselect locale set en_GB.UTF-8 
Setting LANG to en_GB.UTF-8 ...
root #eselect locale list 
  [1] C
  [2] POSIX
  [3] en_GB.utf8
  [4] en_GB.UTF-8 *
  [ ] (free form)

Running the following command will update the variables in the shell:

root #env-update && source /etc/profile 
>>> Regenerating /etc/ld.so.cache...

That is everything. The system is now using UTF-8 locales. The next hurdle is the configuration of the applications used from day to day.

Application support

When Unicode first started gaining momentum in the software world, multibyte character sets were not well suited to languages like C, which is the base language of most commonly used programs. Even today, some programs are not able to handle UTF-8 properly. Fortunately the majority of programs, especially the common ones, are supported.

(V)FAT

For UTF-8 support in FAT filesystems see the FAT article.

Filenames

For changing the encoding of filenames, app-text/convmv can be used.

root #emerge --ask app-text/convmv

The format of the convmv command is as follows:

root #convmv -f <current-encoding> -t utf-8 <filename>

Substitute iso-8859-1 with the charset being converted from:

root #convmv -f iso-8859-1 -t utf-8 filename

For changing the contents of files, use the iconv utility, it comes bundled with sys-libs/glibc and should be installed on all Gentoo systems. Substitute iso-8859-1 with the charset being converted from. After running the command be sure to check for sane output:

root #iconv -f iso-8859-1 -t utf-8 filename

To convert a file, another file must be created:

root #iconv -f iso-8859-1 -t utf-8 filename > newfile

The recode (app-text/recode) package can also be used for this purpose.

The system console

To enable UTF-8 on the console edit /etc/rc.conf. Set unicode="yes" and read the comments -- it is important to have a font that has a good range of characters to make the most of Unicode. For this to work make sure the Unicode locale has been properly created.

The keymap variable, set in /etc/conf.d/keymaps, should have a Unicode keymap specified.

代码 Example /etc/conf.d/keymaps snippet
## (Change "uk" to the right local layout)
keymap="uk"

Ncurses and Slang

附注
Ignore any mention of Slang in this section if it is not installed or unneeded.

It is wise to add unicode to the global USE flags in /etc/portage/make.conf, and then to re-emerge sys-libs/ncurses and sys-libs/slang. Portage will do this automatically if the --changed-use or --newuse options are used. Run the following command to pull in the packages:

root #emerge --update --deep --newuse @world

We also need to rebuild packages that link to these, now the USE changes have been applied. The tool we use (revdep-rebuild) is part of the app-portage/gentoolkit package.

root #revdep-rebuild --library libncurses.so.5
root #revdep-rebuild --library libslang.so.1

KDE, GNOME, and Xfce

All of the major desktop environments have full Unicode support, and will require no further setup than what has already been covered in this guide. This is because the underlying graphical toolkits (Qt or GTK 2) are UTF-8 aware. Subsequently, all applications running on top of these toolkits should be UTF-8-aware out of the box.

On GTK based applications, the key sequence for hexadecimal Unicode input is Ctrl+Shift+u+<hex digit>. As an example, the unicode character ✔ which has unicode number U+2714 can be written as Ctrl+Shift+u+2714+ENTER, being rendered as ✔. IBus is needed for support in other applications.

X11 and fonts

TrueType fonts have support for Unicode, and most of the fonts that ship with Xorg have extensive character support, although, obviously, not every single glyph available in Unicode has been created for that font.

Also, many font packages in Portage are Unicode aware. See the Fontconfig page for more information on recommended fonts and configuration.

Window managers and terminal emulators

Window managers not built on GTK or Qt generally have very good Unicode support, as they often use the Xft library for handling fonts. If the window manager does not use Xft for fonts, then it is still possible to use the FontSpec mentioned in the previous section as a Unicode font.

Terminal emulators that use Xft and support Unicode are harder to come by. Aside from Konsole and GNOME Terminal, the best options in Portage are x11-terms/rxvt-unicode, x11-terms/xfce4-terminal, gnustep-apps/terminal, x11-terms/mlterm, or plain x11-terms/xterm when built with the unicode USE flag and invoked as uxterm. app-misc/screen supports UTF-8 too, when invoked as screen -U or the following is put into the ~/.screenrc:

代码 ~/.screenrc for UTF-8
defutf8 on

Vim, emacs, xemacs, and nano

Vim provides full UTF-8 support, and also has builtin detection of UTF-8 files. For further information in Vim, use :help mbyte.txt.

GNU Emacs since version 23 and XEmacs version 21.5 have full UTF-8 support. GNU Emacs 24 also supports editing bidirectional text.

Nano has provided full UTF-8 support since version 1.3.6.

Shells

Currently, Bash provides full Unicode support through the GNU readline library. Z Shell offers Unicode support with the unicode USE flag.

The C shell, tcsh and ksh do not provide UTF-8 support at all.

Irssi

Irssi has complete UTF-8 support, although it does require a user to set an option.

[irssi]set term_charset UTF-8

For channels where non-ASCII characters are often exchanged in non-UTF-8 charsets, the /recode command may be used to convert the characters. Type /help recode for more information.

Mutt

The Mutt mail user agent has very good Unicode support. To use UTF-8 with Mutt, nothing needs to be put in the configuration files. Mutt will work under Unicode environment without modification if all the configuration files (signature included) are UTF-8 encoded.

附注
It is still possible to see '?' in mails read with Mutt. This is a result of people using a mail client which does not indicate the used charset. There is little one can do about this than to ask them to configure their client correctly.

Further information is available from the Mutt Wiki.

links and elinks

These are commonly used text-based browsers, and we shall see how we can enable UTF-8 support on them. On elinks and links, there are two ways to go about this, one using the Setup option from within the browser or editing the config file. To set the option through the browser, open a site with elinks or links and then Alt+S to enter the Setup Menu then select Terminal options, or press T. Scroll down and select the last option UTF-8 I/O by pressing Enter. Then Save and exit the menu. On links one may have to do a repeat Alt+S and then press S to save. The config file option, is shown below.

代码 Enabling UTF-8 for elinks/links
## (For elinks, edit /etc/elinks/elinks.conf or ~/.elinks/elinks.conf and add the following line)
set terminal.linux.utf_8_io = 1
## (For links, edit ~/.links/links.cfg and add the following line)
terminal "xterm" 0 1 0 us-ascii utf-8

Samba

Samba is a software suite which implements the SMB (Server Message Block) protocol for UNIX systems such as Macs, Linux and FreeBSD. The protocol is also sometimes referred to as the Common Internet File System (CIFS). Samba also includes the NetBIOS system - used for file sharing over windows networks.

Add the following lines under the [global] section:

root #nano -w /etc/samba/smb.conf
dos charset = 1255
unix charset = UTF-8
display charset = UTF-8

全部测试

There are numerous UTF-8 test websites around and most of the popular browsers in Gentoo have full UTF-8 support.

When using one of the text-only web browsers, make absolutely sure a Unicode-aware terminal is used.

If certain characters are displayed as boxes with letters or numbers inside, then the current font does not have glyphs for those characters. Instead, it displays a box with the hex code of the UTF-8 symbol.

报告的问题和问题

系统配置文件（在 /etc 中）

Most system configuration files (such as /etc/fstab) do not support UTF-8. It is recommended to stick with the ASCII character set for these files.

外部资源

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