L'UTF-8 è una codifica dei caratteri a lunghezza variabile, il che significa per esempio che vengono utilizzati da 1 a 4 bytes per simbolo. Quindi, il primo byte UTF-8 è utilizzato per codificare caratteri ASCII, garantendo alla codifica piena compatibilità con il codice ASCII. Secondo UTF-8, ASCII e caratteri Latini sono intercambiabili con un piccolo incremento di dimensione dei dati, dato che solo il primo byte è utilizzato. Gli utilizzatori degli alfabeti orientali, come il Giapponese, che hanno assegnato un più ampio range, sono infelici, perchè questo porta ad una ridondanza fino al 50% nei loro dati
Cos'è la codifica caratteri?
I Computer non capiscono il testo di per sè. Al contrario, ogni carattere è rappresentato da un numero. In passato, ogni set di numeri utilizzato per rappresentare alfabeti e caratteri (noto come codice, codifica o set di caratteri) era limitato in dimensione per via dei limiti hardware.
La storia delle codifiche caratteri
Il set più comune (o perlomeno il più accettato) è il codice ASCII (American Standard Code for Information Interchange). E'ritenuto essere lo standard software di maggior successo da sempre. l'ASCII moderno è stato standardizzato nel 1986 (ANSI X3.4, RFC 20, ISO/IEC 646:1991, ECMA-6) dall'American National Standards Institute.
L'ASCII è ristretto a sette bit, ossia utilizza una serie di simboli rappresentabile con sette simboli binari, che forniscono un range da 0 a 127 in decimale. Questo include 32 caratteri di controllo non visibili, la maggior parte tra 0 e 31, più il carattere di controllo finale, DEL o delete a 127. I caratteri da 32 a 126 sono caratteri visibili:uno spazio, segni di punteggiatura, lettere Latine e numeri.
l'ottavo bit in ASCII era usato in origine come bit di parità per controllo errore. Se questo non è desiderato, viene lasciato a 0. Ciò significa che, nel codice ASCII, ogni carattere è rappresentato da un singolo byte.
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 127 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. This is 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.
What is Unicode?
Unicode throws away the traditional single-byte limit of character sets. It uses 17 "planes" of 65,536 code points to describe a maximum of 1,114,112 characters. As the first plane, aka. "Basic Multilingual Plane" or BMP, contains almost every character a user will ever need. Many have made the wrong assumption that Unicode was a 16-bit character set.
Unicode has been mapped in many different ways, but the two most common are UTF (Unicode Transformation Format) and UCS (Universal Character Set). A number after UTF indicates the number of bits in one unit, while the number after UCS indicates the number of bytes. UTF-8 has become the most widespread means for the interchange of Unicode text as a result of its eight-bit clean nature; it is therefore the subject of this document.
What UTF-8 can do
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.
Setting up UTF-8 in Gentoo
Finding or creating UTF-8 locales
Now that the principles behind Unicode have been laid out, get ready to start using UTF-8 locally!
For users interested in more knowledge further explanation can be found in the Gentoo Localization Guide.
Next, the user needs to decide whether a UTF-8 locale is available for the language of choice, or whether one needs to be generated.
locale -a | grep 'en_GB'
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.
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:
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.
* Generating 1 locales (this might take a while) with 1 jobs * (1/1) Generating en_GB.UTF-8 ... [ ok ] * Generation complete
Setting the 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:
## (As always, change "en_GB.UTF-8" to the appropriate locale value; each language has a different value!) LANG="en_GB.UTF-8"
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:
>>> Regenerating /etc/ld.so.cache...
Now, run locale with no arguments to see if the correct variables have been loaded in the environment:
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:
eselect locale list
 C  POSIX *  en_GB.utf8 [ ] (free form)
Using eselect setting the locale is as simple as listing them. Once the correct locale has been determined invoke:
eselect locale set 3
Setting LANG to en_GB.utf8 ...
Check the result:
eselect locale list
 C  POSIX  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:
eselect locale set en_GB.UTF-8
Setting LANG to en_GB.UTF-8 ...
eselect locale list
 C  POSIX  en_GB.utf8  en_GB.UTF-8 * [ ] (free form)
Running the following command will update the variables in the shell:
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.
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.
For changing the encoding of filenames, app-text/convmv can be used.
emerge --ask app-text/convmv
The format of the convmv command is as follows:
convmv -f <current-encoding> -t utf-8 <filename>
iso-8859-1 with the charset being converted from:
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:
iconv -f iso-8859-1 -t utf-8 filename
To convert a file, another file must be created:
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.
## (Change "uk" to the right local layout) keymap="uk"
Ncurses and Slang
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
--newuse options are used. Run the following command to pull in the packages:
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.
revdep-rebuild --library libncurses.so.5
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+
ENTER, being rendered as
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:
Vim, emacs, xemacs, and nano
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.
The C shell, tcsh and ksh do not provide UTF-8 support at all.
Irssi has complete UTF-8 support, although it does require a user to set an option.
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.
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.
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.
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.
## (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 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
nano -w /etc/samba/smb.conf
dos charset = 1255 unix charset = UTF-8 display charset = UTF-8
Testing it all out
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.
Reported issues and problems
System configuration files (in /etc)
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.
This page is based on a document formerly found on our main website gentoo.org.
The following people contributed to the original document: Thomas Martin, Alexander Simonov, Shyam Mani,
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.